\A{iref} x86 Instruction Reference

This appendix provides a complete list of the machine instructions
which NASM will assemble, and a short description of the function of
each one.

It is not intended to be an exhaustive documentation on the fine
details of the instructions' function, such as which exceptions they
can trigger: for such documentation, you should go to Intel's Web
site, \W{http://developer.intel.com/design/Pentium4/manuals/}\c{http://developer.intel.com/design/Pentium4/manuals/}.

Instead, this appendix is intended primarily to provide
documentation on the way the instructions may be used within NASM.
For example, looking up \c{LOOP} will tell you that NASM allows
\c{CX} or \c{ECX} to be specified as an optional second argument to
the \c{LOOP} instruction, to enforce which of the two possible
counter registers should be used if the default is not the one
desired.

The instructions are not quite listed in alphabetical order, since
groups of instructions with similar functions are lumped together in
the same entry. Most of them don't move very far from their
alphabetic position because of this.


\H{iref-opr} Key to Operand Specifications

The instruction descriptions in this appendix specify their operands
using the following notation:

\b Registers: \c{reg8} denotes an 8-bit \i{general purpose
register}, \c{reg16} denotes a 16-bit general purpose register,
\c{reg32} a 32-bit one and \c{reg64} a 64-bit one. \c{fpureg} denotes
one of the eight FPU stack registers, \c{mmxreg} denotes one of the
eight 64-bit MMX registers, and \c{segreg} denotes a segment register.
\c{xmmreg} denotes one of the 8, or 16 in x64 long mode, SSE XMM registers.
In addition, some registers (such as \c{AL}, \c{DX}, \c{ECX} or \c{RAX})
may be specified explicitly.

\b Immediate operands: \c{imm} denotes a generic \i{immediate operand}.
\c{imm8}, \c{imm16} and \c{imm32} are used when the operand is
intended to be a specific size. For some of these instructions, NASM
needs an explicit specifier: for example, \c{ADD ESP,16} could be
interpreted as either \c{ADD r/m32,imm32} or \c{ADD r/m32,imm8}.
NASM chooses the former by default, and so you must specify \c{ADD
ESP,BYTE 16} for the latter. There is a special case of the allowance
of an \c{imm64} for particular x64 versions of the MOV instruction.

\b Memory references: \c{mem} denotes a generic \i{memory reference};
\c{mem8}, \c{mem16}, \c{mem32}, \c{mem64} and \c{mem80} are used
when the operand needs to be a specific size. Again, a specifier is
needed in some cases: \c{DEC [address]} is ambiguous and will be
rejected by NASM. You must specify \c{DEC BYTE [address]}, \c{DEC
WORD [address]} or \c{DEC DWORD [address]} instead.

\b \i{Restricted memory references}: one form of the \c{MOV}
instruction allows a memory address to be specified \e{without}
allowing the normal range of register combinations and effective
address processing. This is denoted by \c{memoffs8}, \c{memoffs16},
\c{memoffs32} or \c{memoffs64}.

\b Register or memory choices: many instructions can accept either a
register \e{or} a memory reference as an operand. \c{r/m8} is
shorthand for \c{reg8/mem8}; similarly \c{r/m16} and \c{r/m32}.
On legacy x86 modes, \c{r/m64} is MMX-related, and is shorthand for
\c{mmxreg/mem64}. When utilizing the x86-64 architecture extension,
\c{r/m64} denotes use of a 64-bit GPR as well, and is shorthand for
\c{reg64/mem64}.


\H{iref-opc} Key to Opcode Descriptions

This appendix also provides the opcodes which NASM will generate for
each form of each instruction. The opcodes are listed in the
following way:

\b A hex number, such as \c{3F}, indicates a fixed byte containing
that number.

\b A hex number followed by \c{+r}, such as \c{C8+r}, indicates that
one of the operands to the instruction is a register, and the
`register value' of that register should be added to the hex number
to produce the generated byte. For example, EDX has register value
2, so the code \c{C8+r}, when the register operand is EDX, generates
the hex byte \c{CA}. Register values for specific registers are
given in \k{iref-rv}.

\b A hex number followed by \c{+cc}, such as \c{40+cc}, indicates
that the instruction name has a condition code suffix, and the
numeric representation of the condition code should be added to the
hex number to produce the generated byte. For example, the code
\c{40+cc}, when the instruction contains the \c{NE} condition,
generates the hex byte \c{45}. Condition codes and their numeric
representations are given in \k{iref-cc}.

\b A slash followed by a digit, such as \c{/2}, indicates that one
of the operands to the instruction is a memory address or register
(denoted \c{mem} or \c{r/m}, with an optional size). This is to be
encoded as an effective address, with a \i{ModR/M byte}, an optional
\i{SIB byte}, and an optional displacement, and the spare (register)
field of the ModR/M byte should be the digit given (which will be
from 0 to 7, so it fits in three bits). The encoding of effective
addresses is given in \k{iref-ea}.

\b The code \c{/r} combines the above two: it indicates that one of
the operands is a memory address or \c{r/m}, and another is a
register, and that an effective address should be generated with the
spare (register) field in the ModR/M byte being equal to the
`register value' of the register operand. The encoding of effective
addresses is given in \k{iref-ea}; register values are given in
\k{iref-rv}.

\b The codes \c{ib}, \c{iw} and \c{id} indicate that one of the
operands to the instruction is an immediate value, and that this is
to be encoded as a byte, little-endian word or little-endian
doubleword respectively.

\b The codes \c{rb}, \c{rw} and \c{rd} indicate that one of the
operands to the instruction is an immediate value, and that the
\e{difference} between this value and the address of the end of the
instruction is to be encoded as a byte, word or doubleword
respectively. Where the form \c{rw/rd} appears, it indicates that
either \c{rw} or \c{rd} should be used according to whether assembly
is being performed in \c{BITS 16} or \c{BITS 32} state respectively.

\b The codes \c{ow} and \c{od} indicate that one of the operands to
the instruction is a reference to the contents of a memory address
specified as an immediate value: this encoding is used in some forms
of the \c{MOV} instruction in place of the standard
effective-address mechanism. The displacement is encoded as a word
or doubleword. Again, \c{ow/od} denotes that \c{ow} or \c{od} should
be chosen according to the \c{BITS} setting.

\b The codes \c{o16} and \c{o32} indicate that the given form of the
instruction should be assembled with operand size 16 or 32 bits. In
other words, \c{o16} indicates a \c{66} prefix in \c{BITS 32} state,
but generates no code in \c{BITS 16} state; and \c{o32} indicates a
\c{66} prefix in \c{BITS 16} state but generates nothing in \c{BITS
32}.

\b The codes \c{a16} and \c{a32}, similarly to \c{o16} and \c{o32},
indicate the address size of the given form of the instruction.
Where this does not match the \c{BITS} setting, a \c{67} prefix is
required. Please note that \c{a16} is useless in long mode as
16-bit addressing is depreciated on the x86-64 architecture extension.


\S{iref-rv} Register Values

Where an instruction requires a register value, it is already
implicit in the encoding of the rest of the instruction what type of
register is intended: an 8-bit general-purpose register, a segment
register, a debug register, an MMX register, or whatever. Therefore
there is no problem with registers of different types sharing an
encoding value.

Please note that for the register classes listed below, the register
extensions (REX) classes require the use of the REX prefix, in which
is only available when in long mode on the x86-64 processor. This
pretty much goes for any register that has a number higher than 7.

The encodings for the various classes of register are:

\b 8-bit general registers: \c{AL} is 0, \c{CL} is 1, \c{DL} is 2,
\c{BL} is 3, \c{AH} is 4, \c{CH} is 5, \c{DH} is 6 and \c{BH} is
7. Please note that \c{AH}, \c{BH}, \c{CH} and \c{DH} are not
addressable when using the REX prefix in long mode.

\b 8-bit general register extensions (REX): \c{SPL} is 4, \c{BPL} is 5,
\c{SIL} is 6, \c{DIL} is 7, \c{R8B} is 8, \c{R9B} is 9, \c{R10B} is 10,
\c{R11B} is 11, \c{R12B} is 12, \c{R13B} is 13, \c{R14B} is 14 and
\c{R15B} is 15.

\b 16-bit general registers: \c{AX} is 0, \c{CX} is 1, \c{DX} is 2,
\c{BX} is 3, \c{SP} is 4, \c{BP} is 5, \c{SI} is 6, and \c{DI} is 7.

\b 16-bit general register extensions (REX): \c{R8W} is 8, \c{R9W} is 9,
\c{R10w} is 10, \c{R11W} is 11, \c{R12W} is 12, \c{R13W} is 13, \c{R14W}
is 14 and \c{R15W} is 15.

\b 32-bit general registers: \c{EAX} is 0, \c{ECX} is 1, \c{EDX} is
2, \c{EBX} is 3, \c{ESP} is 4, \c{EBP} is 5, \c{ESI} is 6, and
\c{EDI} is 7.

\b 32-bit general register extensions (REX): \c{R8D} is 8, \c{R9D} is 9,
\c{R10D} is 10, \c{R11D} is 11, \c{R12D} is 12, \c{R13D} is 13, \c{R14D}
is 14 and \c{R15D} is 15.

\b 64-bit general register extensions (REX): \c{RAX} is 0, \c{RCX} is 1,
\c{RDX} is 2, \c{RBX} is 3, \c{RSP} is 4, \c{RBP} is 5, \c{RSI} is 6,
\c{RDI} is 7, \c{R8} is 8, \c{R9} is 9, \c{R10} is 10, \c{R11} is 11,
\c{R12} is 12, \c{R13} is 13, \c{R14} is 14 and \c{R15} is 15.

\b \i{Segment registers}: \c{ES} is 0, \c{CS} is 1, \c{SS} is 2, \c{DS}
is 3, \c{FS} is 4, and \c{GS} is 5.

\b \I{floating-point, registers}Floating-point registers: \c{ST0}
is 0, \c{ST1} is 1, \c{ST2} is 2, \c{ST3} is 3, \c{ST4} is 4,
\c{ST5} is 5, \c{ST6} is 6, and \c{ST7} is 7.

\b 64-bit \i{MMX registers}: \c{MM0} is 0, \c{MM1} is 1, \c{MM2} is 2,
\c{MM3} is 3, \c{MM4} is 4, \c{MM5} is 5, \c{MM6} is 6, and \c{MM7}
is 7.

\b 128-bit \i{XMM (SSE) registers}: \c{XMM0} is 0, \c{XMM1} is 1,
\c{XMM2} is 2, \c{XMM3} is 3, \c{XMM4} is 4, \c{XMM5} is 5, \c{XMM6} is
6 and \c{XMM7} is 7.

\b 128-bit \i{XMM (SSE) register} extensions (REX): \c{XMM8} is 8,
\c{XMM9} is 9, \c{XMM10} is 10, \c{XMM11} is 11, \c{XMM12} is 12,
\c{XMM13} is 13, \c{XMM14} is 14 and \c{XMM15} is 15.

\b \i{Control registers}: \c{CR0} is 0, \c{CR2} is 2, \c{CR3} is 3,
and \c{CR4} is 4.

\b \i{Control register} extensions: \c{CR8} is 8.

\b \i{Debug registers}: \c{DR0} is 0, \c{DR1} is 1, \c{DR2} is 2,
\c{DR3} is 3, \c{DR6} is 6, and \c{DR7} is 7.

\b \i{Test registers}: \c{TR3} is 3, \c{TR4} is 4, \c{TR5} is 5,
\c{TR6} is 6, and \c{TR7} is 7.

(Note that wherever a register name contains a number, that number
is also the register value for that register.)


\S{iref-cc} \i{Condition Codes}

The available condition codes are given here, along with their
numeric representations as part of opcodes. Many of these condition
codes have synonyms, so several will be listed at a time.

In the following descriptions, the word `either', when applied to two
possible trigger conditions, is used to mean `either or both'. If
`either but not both' is meant, the phrase `exactly one of' is used.

\b \c{O} is 0 (trigger if the overflow flag is set); \c{NO} is 1.

\b \c{B}, \c{C} and \c{NAE} are 2 (trigger if the carry flag is
set); \c{AE}, \c{NB} and \c{NC} are 3.

\b \c{E} and \c{Z} are 4 (trigger if the zero flag is set); \c{NE}
and \c{NZ} are 5.

\b \c{BE} and \c{NA} are 6 (trigger if either of the carry or zero
flags is set); \c{A} and \c{NBE} are 7.

\b \c{S} is 8 (trigger if the sign flag is set); \c{NS} is 9.

\b \c{P} and \c{PE} are 10 (trigger if the parity flag is set);
\c{NP} and \c{PO} are 11.

\b \c{L} and \c{NGE} are 12 (trigger if exactly one of the sign and
overflow flags is set); \c{GE} and \c{NL} are 13.

\b \c{LE} and \c{NG} are 14 (trigger if either the zero flag is set,
or exactly one of the sign and overflow flags is set); \c{G} and
\c{NLE} are 15.

Note that in all cases, the sense of a condition code may be
reversed by changing the low bit of the numeric representation.

For details of when an instruction sets each of the status flags,
see the individual instruction, plus the Status Flags reference
in \k{iref-Flags}


\S{iref-SSE-cc} \i{SSE Condition Predicates}

The condition predicates for SSE comparison instructions are the
codes used as part of the opcode, to determine what form of
comparison is being carried out. In each case, the imm8 value is
the final byte of the opcode encoding, and the predicate is the
code used as part of the mnemonic for the instruction (equivalent
to the "cc" in an integer instruction that used a condition code).
The instructions that use this will give details of what the various
mnemonics are, this table is used to help you work out details of what
is happening.

\c Predi-  imm8  Description Relation where:   Emula- Result   QNaN
\c  cate  Encod-             A Is 1st Operand  tion   if NaN   Signal
\c         ing               B Is 2nd Operand         Operand  Invalid
\c
\c EQ     000B   equal       A = B                    False     No
\c
\c LT     001B   less-than   A < B                    False     Yes
\c
\c LE     010B   less-than-  A <= B                   False     Yes
\c                or-equal
\c
\c ---    ----   greater     A > B             Swap   False     Yes
\c               than                          Operands,
\c                                             Use LT
\c
\c ---    ----   greater-    A >= B            Swap   False     Yes
\c               than-or-equal                 Operands,
\c                                             Use LE
\c
\c UNORD  011B   unordered   A, B = Unordered         True      No
\c
\c NEQ    100B   not-equal   A != B                   True      No
\c
\c NLT    101B   not-less-   NOT(A < B)               True      Yes
\c               than
\c
\c NLE    110B   not-less-   NOT(A <= B)              True      Yes
\c               than-or-
\c               equal
\c
\c ---    ----   not-greater NOT(A > B)        Swap   True      Yes
\c               than                          Operands,
\c                                             Use NLT
\c
\c ---    ----   not-greater NOT(A >= B)       Swap   True      Yes
\c               than-                         Operands,
\c               or-equal                      Use NLE
\c
\c ORD    111B   ordered      A , B = Ordered         False     No

The unordered relationship is true when at least one of the two
values being compared is a NaN or in an unsupported format.

Note that the comparisons which are listed as not having a predicate
or encoding can only be achieved through software emulation, as
described in the "emulation" column. Note in particular that an
instruction such as \c{greater-than} is not the same as \c{NLE}, as,
unlike with the \c{CMP} instruction, it has to take into account the
possibility of one operand containing a NaN or an unsupported numeric
format.


\S{iref-Flags} \i{Status Flags}

The status flags provide some information about the result of the
arithmetic instructions. This information can be used by conditional
instructions (such a \c{Jcc} and \c{CMOVcc}) as well as by some of
the other instructions (such as \c{ADC} and \c{INTO}).

There are 6 status flags:

\c CF - Carry flag.

Set if an arithmetic operation generates a
carry or a borrow out of the most-significant bit of the result;
cleared otherwise. This flag indicates an overflow condition for
unsigned-integer arithmetic. It is also used in multiple-precision
arithmetic.

\c PF - Parity flag.

Set if the least-significant byte of the result contains an even
number of 1 bits; cleared otherwise.

\c AF - Adjust flag.

Set if an arithmetic operation generates a carry or a borrow
out of bit 3 of the result; cleared otherwise. This flag is used
in binary-coded decimal (BCD) arithmetic.

\c ZF - Zero flag.

Set if the result is zero; cleared otherwise.

\c SF - Sign flag.

Set equal to the most-significant bit of the result, which is the
sign bit of a signed integer. (0 indicates a positive value and 1
indicates a negative value.)

\c OF - Overflow flag.

Set if the integer result is too large a positive number or too
small a negative number (excluding the sign-bit) to fit in the
destination operand; cleared otherwise. This flag indicates an
overflow condition for signed-integer (two's complement) arithmetic.


\S{iref-ea} Effective Address Encoding: \i{ModR/M} and \i{SIB}

An \i{effective address} is encoded in up to three parts: a ModR/M
byte, an optional SIB byte, and an optional byte, word or doubleword
displacement field.

The ModR/M byte consists of three fields: the \c{mod} field, ranging
from 0 to 3, in the upper two bits of the byte, the \c{r/m} field,
ranging from 0 to 7, in the lower three bits, and the spare
(register) field in the middle (bit 3 to bit 5). The spare field is
not relevant to the effective address being encoded, and either
contains an extension to the instruction opcode or the register
value of another operand.

The ModR/M system can be used to encode a direct register reference
rather than a memory access. This is always done by setting the
\c{mod} field to 3 and the \c{r/m} field to the register value of
the register in question (it must be a general-purpose register, and
the size of the register must already be implicit in the encoding of
the rest of the instruction). In this case, the SIB byte and
displacement field are both absent.

In 16-bit addressing mode (either \c{BITS 16} with no \c{67} prefix,
or \c{BITS 32} with a \c{67} prefix), the SIB byte is never used.
The general rules for \c{mod} and \c{r/m} (there is an exception,
given below) are:

\b The \c{mod} field gives the length of the displacement field: 0
means no displacement, 1 means one byte, and 2 means two bytes.

\b The \c{r/m} field encodes the combination of registers to be
added to the displacement to give the accessed address: 0 means
\c{BX+SI}, 1 means \c{BX+DI}, 2 means \c{BP+SI}, 3 means \c{BP+DI},
4 means \c{SI} only, 5 means \c{DI} only, 6 means \c{BP} only, and 7
means \c{BX} only.

However, there is a special case:

\b If \c{mod} is 0 and \c{r/m} is 6, the effective address encoded
is not \c{[BP]} as the above rules would suggest, but instead
\c{[disp16]}: the displacement field is present and is two bytes
long, and no registers are added to the displacement.

Therefore the effective address \c{[BP]} cannot be encoded as
efficiently as \c{[BX]}; so if you code \c{[BP]} in a program, NASM
adds a notional 8-bit zero displacement, and sets \c{mod} to 1,
\c{r/m} to 6, and the one-byte displacement field to 0.

In 32-bit addressing mode (either \c{BITS 16} with a \c{67} prefix,
or \c{BITS 32} with no \c{67} prefix) the general rules (again,
there are exceptions) for \c{mod} and \c{r/m} are:

\b The \c{mod} field gives the length of the displacement field: 0
means no displacement, 1 means one byte, and 2 means four bytes.

\b If only one register is to be added to the displacement, and it
is not \c{ESP}, the \c{r/m} field gives its register value, and the
SIB byte is absent. If the \c{r/m} field is 4 (which would encode
\c{ESP}), the SIB byte is present and gives the combination and
scaling of registers to be added to the displacement.

If the SIB byte is present, it describes the combination of
registers (an optional base register, and an optional index register
scaled by multiplication by 1, 2, 4 or 8) to be added to the
displacement. The SIB byte is divided into the \c{scale} field, in
the top two bits, the \c{index} field in the next three, and the
\c{base} field in the bottom three. The general rules are:

\b The \c{base} field encodes the register value of the base
register.

\b The \c{index} field encodes the register value of the index
register, unless it is 4, in which case no index register is used
(so \c{ESP} cannot be used as an index register).

\b The \c{scale} field encodes the multiplier by which the index
register is scaled before adding it to the base and displacement: 0
encodes a multiplier of 1, 1 encodes 2, 2 encodes 4 and 3 encodes 8.

The exceptions to the 32-bit encoding rules are:

\b If \c{mod} is 0 and \c{r/m} is 5, the effective address encoded
is not \c{[EBP]} as the above rules would suggest, but instead
\c{[disp32]}: the displacement field is present and is four bytes
long, and no registers are added to the displacement.

\b If \c{mod} is 0, \c{r/m} is 4 (meaning the SIB byte is present)
and \c{base} is 5, the effective address encoded is not
\c{[EBP+index]} as the above rules would suggest, but instead
\c{[disp32+index]}: the displacement field is present and is four
bytes long, and there is no base register (but the index register is
still processed in the normal way).


\S{iref-rex} Register Extensions: The \i{REX} Prefix

The Register Extensions, or \i{REX} for short, prefix is the means
of accessing extended registers on the x86-64 architecture. \i{REX}
is considered an instruction prefix, but is required to be after
all other prefixes and thus immediately before the first instruction
opcode itself. So overall, \i{REX} can be thought of as an "Opcode
Prefix" instead. The \i{REX} prefix itself is indicated by a value
of 0x4X, where X is one of 16 different combinations of the actual
\i{REX} flags.

The \i{REX} prefix flags consist of four 1-bit extensions fields.
These flags are found in the lower nibble of the actual \i{REX}
prefix opcode. Below is the list of \i{REX} prefix flags, from
high bit to low bit.

\c{REX.W}: When set, this flag indicates the use of a 64-bit operand,
as opposed to the default of using 32-bit operands as found in 32-bit
Protected Mode.

\c{REX.R}: When set, this flag extends the \c{reg (spare)} field of
the \c{ModRM} byte. Overall, this raises the amount of addressable
registers in this field from 8 to 16.

\c{REX.X}: When set, this flag extends the \c{index} field of the
\c{SIB} byte. Overall, this raises the amount of addressable
registers in this field from 8 to 16.

\c{REX.B}: When set, this flag extends the \c{r/m} field of the
\c{ModRM} byte. This flag can also represent an extension to the
opcode register \c{(/r)} field. The determination of which is used
varies depending on which instruction is used. Overall, this raises
the amount of addressable registers in these fields from 8 to 16.

Interal use of the \i{REX} prefix by the processor is consistent,
yet non-trivial. Most instructions use the \i{REX} prefix as
indicated by the above flags. Some instructions require the \i{REX}
prefix to be present even if the flags are empty. Some instructions
default to a 64-bit operand and require the \i{REX} prefix only for
actual register extensions, and thus ignores the \c{REX.W} field
completely.

At any rate, NASM is designed to handle, and fully supports, the
\i{REX} prefix internally. Please read the appropriate processor
documentation for further information on the \i{REX} prefix.

You may have noticed that opcodes 0x40 through 0x4F are actually
opcodes for the INC/DEC instructions for each General Purpose
Register. This is, of course, correct... for legacy x86. While
in long mode, opcodes 0x40 through 0x4F are reserved for use as
the REX prefix. The other opcode forms of the INC/DEC instructions
are used instead.


\H{iref-flg} Key to Instruction Flags

Given along with each instruction in this appendix is a set of
flags, denoting the type of the instruction. The types are as follows:

\b \c{8086}, \c{186}, \c{286}, \c{386}, \c{486}, \c{PENT} and \c{P6}
denote the lowest processor type that supports the instruction. Most
instructions run on all processors above the given type; those that
do not are documented. The Pentium II contains no additional
instructions beyond the P6 (Pentium Pro); from the point of view of
its instruction set, it can be thought of as a P6 with MMX
capability.

\b \c{3DNOW} indicates that the instruction is a 3DNow! one, and will
run on the AMD K6-2 and later processors. ATHLON extensions to the
3DNow! instruction set are documented as such.

\b \c{CYRIX} indicates that the instruction is specific to Cyrix
processors, for example the extra MMX instructions in the Cyrix
extended MMX instruction set.

\b \c{FPU} indicates that the instruction is a floating-point one,
and will only run on machines with a coprocessor (automatically
including 486DX, Pentium and above).

\b \c{KATMAI} indicates that the instruction was introduced as part
of the Katmai New Instruction set. These instructions are available
on the Pentium III and later processors. Those which are not
specifically SSE instructions are also available on the AMD Athlon.

\b \c{MMX} indicates that the instruction is an MMX one, and will
run on MMX-capable Pentium processors and the Pentium II.

\b \c{PRIV} indicates that the instruction is a protected-mode
management instruction. Many of these may only be used in protected
mode, or only at privilege level zero.

\b \c{SSE} and \c{SSE2} indicate that the instruction is a Streaming
SIMD Extension instruction. These instructions operate on multiple
values in a single operation. SSE was introduced with the Pentium III
and SSE2 was introduced with the Pentium 4.

\b \c{UNDOC} indicates that the instruction is an undocumented one,
and not part of the official Intel Architecture; it may or may not
be supported on any given machine.

\b \c{WILLAMETTE} indicates that the instruction was introduced as
part of the new instruction set in the Pentium 4 and Intel Xeon
processors. These instructions are also known as SSE2 instructions.

\b \c{X64} indicates that the instruction was introduced as part of
the new instruction set in the x86-64 architecture extension,
commonly referred to as x64, AMD64 or EM64T.


\H{iref-inst} x86 Instruction Set


\S{insAAA} \i\c{AAA}, \i\c{AAS}, \i\c{AAM}, \i\c{AAD}: ASCII
Adjustments

\c AAA                           ; 37                   [8086]

\c AAS                           ; 3F                   [8086]

\c AAD                           ; D5 0A                [8086]
\c AAD imm                       ; D5 ib                [8086]

\c AAM                           ; D4 0A                [8086]
\c AAM imm                       ; D4 ib                [8086]

These instructions are used in conjunction with the add, subtract,
multiply and divide instructions to perform binary-coded decimal
arithmetic in \e{unpacked} (one BCD digit per byte - easy to
translate to and from \c{ASCII}, hence the instruction names) form.
There are also packed BCD instructions \c{DAA} and \c{DAS}: see
\k{insDAA}.

\b \c{AAA} (ASCII Adjust After Addition) should be used after a
one-byte \c{ADD} instruction whose destination was the \c{AL}
register: by means of examining the value in the low nibble of
\c{AL} and also the auxiliary carry flag \c{AF}, it determines
whether the addition has overflowed, and adjusts it (and sets
the carry flag) if so. You can add long BCD strings together
by doing \c{ADD}/\c{AAA} on the low digits, then doing
\c{ADC}/\c{AAA} on each subsequent digit.

\b \c{AAS} (ASCII Adjust AL After Subtraction) works similarly to
\c{AAA}, but is for use after \c{SUB} instructions rather than
\c{ADD}.

\b \c{AAM} (ASCII Adjust AX After Multiply) is for use after you
have multiplied two decimal digits together and left the result
in \c{AL}: it divides \c{AL} by ten and stores the quotient in
\c{AH}, leaving the remainder in \c{AL}. The divisor 10 can be
changed by specifying an operand to the instruction: a particularly
handy use of this is \c{AAM 16}, causing the two nibbles in \c{AL}
to be separated into \c{AH} and \c{AL}.

\b \c{AAD} (ASCII Adjust AX Before Division) performs the inverse
operation to \c{AAM}: it multiplies \c{AH} by ten, adds it to
\c{AL}, and sets \c{AH} to zero. Again, the multiplier 10 can
be changed.


\S{insADC} \i\c{ADC}: Add with Carry

\c ADC r/m8,reg8                 ; 10 /r                [8086]
\c ADC r/m16,reg16               ; o16 11 /r            [8086]
\c ADC r/m32,reg32               ; o32 11 /r            [386]

\c ADC reg8,r/m8                 ; 12 /r                [8086]
\c ADC reg16,r/m16               ; o16 13 /r            [8086]
\c ADC reg32,r/m32               ; o32 13 /r            [386]

\c ADC r/m8,imm8                 ; 80 /2 ib             [8086]
\c ADC r/m16,imm16               ; o16 81 /2 iw         [8086]
\c ADC r/m32,imm32               ; o32 81 /2 id         [386]

\c ADC r/m16,imm8                ; o16 83 /2 ib         [8086]
\c ADC r/m32,imm8                ; o32 83 /2 ib         [386]

\c ADC AL,imm8                   ; 14 ib                [8086]
\c ADC AX,imm16                  ; o16 15 iw            [8086]
\c ADC EAX,imm32                 ; o32 15 id            [386]

\c{ADC} performs integer addition: it adds its two operands
together, plus the value of the carry flag, and leaves the result in
its destination (first) operand. The destination operand can be a
register or a memory location. The source operand can be a register,
a memory location or an immediate value.

The flags are set according to the result of the operation: in
particular, the carry flag is affected and can be used by a
subsequent \c{ADC} instruction.

In the forms with an 8-bit immediate second operand and a longer
first operand, the second operand is considered to be signed, and is
sign-extended to the length of the first operand. In these cases,
the \c{BYTE} qualifier is necessary to force NASM to generate this
form of the instruction.

To add two numbers without also adding the contents of the carry
flag, use \c{ADD} (\k{insADD}).


\S{insADD} \i\c{ADD}: Add Integers

\c ADD r/m8,reg8                 ; 00 /r                [8086]
\c ADD r/m16,reg16               ; o16 01 /r            [8086]
\c ADD r/m32,reg32               ; o32 01 /r            [386]

\c ADD reg8,r/m8                 ; 02 /r                [8086]
\c ADD reg16,r/m16               ; o16 03 /r            [8086]
\c ADD reg32,r/m32               ; o32 03 /r            [386]

\c ADD r/m8,imm8                 ; 80 /7 ib             [8086]
\c ADD r/m16,imm16               ; o16 81 /7 iw         [8086]
\c ADD r/m32,imm32               ; o32 81 /7 id         [386]

\c ADD r/m16,imm8                ; o16 83 /7 ib         [8086]
\c ADD r/m32,imm8                ; o32 83 /7 ib         [386]

\c ADD AL,imm8                   ; 04 ib                [8086]
\c ADD AX,imm16                  ; o16 05 iw            [8086]
\c ADD EAX,imm32                 ; o32 05 id            [386]

\c{ADD} performs integer addition: it adds its two operands
together, and leaves the result in its destination (first) operand.
The destination operand can be a register or a memory location.
The source operand can be a register, a memory location or an
immediate value.

The flags are set according to the result of the operation: in
particular, the carry flag is affected and can be used by a
subsequent \c{ADC} instruction.

In the forms with an 8-bit immediate second operand and a longer
first operand, the second operand is considered to be signed, and is
sign-extended to the length of the first operand. In these cases,
the \c{BYTE} qualifier is necessary to force NASM to generate this
form of the instruction.


\S{insADDPD} \i\c{ADDPD}: ADD Packed Double-Precision FP Values

\c ADDPD xmm1,xmm2/mem128        ; 66 0F 58 /r     [WILLAMETTE,SSE2]

\c{ADDPD} performs addition on each of two packed double-precision
FP value pairs.

\c    dst[0-63]   := dst[0-63]   + src[0-63],
\c    dst[64-127] := dst[64-127] + src[64-127].

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 128-bit memory location.


\S{insADDPS} \i\c{ADDPS}: ADD Packed Single-Precision FP Values

\c ADDPS xmm1,xmm2/mem128        ; 0F 58 /r        [KATMAI,SSE]

\c{ADDPS} performs addition on each of four packed single-precision
FP value pairs

\c    dst[0-31]   := dst[0-31]   + src[0-31],
\c    dst[32-63]  := dst[32-63]  + src[32-63],
\c    dst[64-95]  := dst[64-95]  + src[64-95],
\c    dst[96-127] := dst[96-127] + src[96-127].

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 128-bit memory location.


\S{insADDSD} \i\c{ADDSD}: ADD Scalar Double-Precision FP Values

\c ADDSD xmm1,xmm2/mem64         ; F2 0F 58 /r     [KATMAI,SSE]

\c{ADDSD} adds the low double-precision FP values from the source
and destination operands and stores the double-precision FP result
in the destination operand.

\c    dst[0-63]   := dst[0-63] + src[0-63],
\c    dst[64-127) remains unchanged.

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 64-bit memory location.


\S{insADDSS} \i\c{ADDSS}: ADD Scalar Single-Precision FP Values

\c ADDSS xmm1,xmm2/mem32         ; F3 0F 58 /r     [WILLAMETTE,SSE2]

\c{ADDSS} adds the low single-precision FP values from the source
and destination operands and stores the single-precision FP result
in the destination operand.

\c    dst[0-31]   := dst[0-31] + src[0-31],
\c    dst[32-127] remains unchanged.

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 32-bit memory location.


\S{insAND} \i\c{AND}: Bitwise AND

\c AND r/m8,reg8                 ; 20 /r                [8086]
\c AND r/m16,reg16               ; o16 21 /r            [8086]
\c AND r/m32,reg32               ; o32 21 /r            [386]

\c AND reg8,r/m8                 ; 22 /r                [8086]
\c AND reg16,r/m16               ; o16 23 /r            [8086]
\c AND reg32,r/m32               ; o32 23 /r            [386]

\c AND r/m8,imm8                 ; 80 /4 ib             [8086]
\c AND r/m16,imm16               ; o16 81 /4 iw         [8086]
\c AND r/m32,imm32               ; o32 81 /4 id         [386]

\c AND r/m16,imm8                ; o16 83 /4 ib         [8086]
\c AND r/m32,imm8                ; o32 83 /4 ib         [386]

\c AND AL,imm8                   ; 24 ib                [8086]
\c AND AX,imm16                  ; o16 25 iw            [8086]
\c AND EAX,imm32                 ; o32 25 id            [386]

\c{AND} performs a bitwise AND operation between its two operands
(i.e. each bit of the result is 1 if and only if the corresponding
bits of the two inputs were both 1), and stores the result in the
destination (first) operand. The destination operand can be a
register or a memory location. The source operand can be a register,
a memory location or an immediate value.

In the forms with an 8-bit immediate second operand and a longer
first operand, the second operand is considered to be signed, and is
sign-extended to the length of the first operand. In these cases,
the \c{BYTE} qualifier is necessary to force NASM to generate this
form of the instruction.

The \c{MMX} instruction \c{PAND} (see \k{insPAND}) performs the same
operation on the 64-bit \c{MMX} registers.


\S{insANDNPD} \i\c{ANDNPD}: Bitwise Logical AND NOT of
Packed Double-Precision FP Values

\c ANDNPD xmm1,xmm2/mem128       ; 66 0F 55 /r     [WILLAMETTE,SSE2]

\c{ANDNPD} inverts the bits of the two double-precision
floating-point values in the destination register, and then
performs a logical AND between the two double-precision
floating-point values in the source operand and the temporary
inverted result, storing the result in the destination register.

\c    dst[0-63]   := src[0-63]   AND NOT dst[0-63],
\c    dst[64-127] := src[64-127] AND NOT dst[64-127].

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 128-bit memory location.


\S{insANDNPS} \i\c{ANDNPS}: Bitwise Logical AND NOT of
Packed Single-Precision FP Values

\c ANDNPS xmm1,xmm2/mem128       ; 0F 55 /r        [KATMAI,SSE]

\c{ANDNPS} inverts the bits of the four single-precision
floating-point values in the destination register, and then
performs a logical AND between the four single-precision
floating-point values in the source operand and the temporary
inverted result, storing the result in the destination register.

\c    dst[0-31]   := src[0-31]   AND NOT dst[0-31],
\c    dst[32-63]  := src[32-63]  AND NOT dst[32-63],
\c    dst[64-95]  := src[64-95]  AND NOT dst[64-95],
\c    dst[96-127] := src[96-127] AND NOT dst[96-127].

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 128-bit memory location.


\S{insANDPD} \i\c{ANDPD}: Bitwise Logical AND For Single FP

\c ANDPD xmm1,xmm2/mem128        ; 66 0F 54 /r     [WILLAMETTE,SSE2]

\c{ANDPD} performs a bitwise logical AND of the two double-precision
floating point values in the source and destination operand, and
stores the result in the destination register.

\c    dst[0-63]   := src[0-63]   AND dst[0-63],
\c    dst[64-127] := src[64-127] AND dst[64-127].

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 128-bit memory location.


\S{insANDPS} \i\c{ANDPS}: Bitwise Logical AND For Single FP

\c ANDPS xmm1,xmm2/mem128        ; 0F 54 /r        [KATMAI,SSE]

\c{ANDPS} performs a bitwise logical AND of the four single-precision
floating point values in the source and destination operand, and
stores the result in the destination register.

\c    dst[0-31]   := src[0-31]   AND dst[0-31],
\c    dst[32-63]  := src[32-63]  AND dst[32-63],
\c    dst[64-95]  := src[64-95]  AND dst[64-95],
\c    dst[96-127] := src[96-127] AND dst[96-127].

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 128-bit memory location.


\S{insARPL} \i\c{ARPL}: Adjust RPL Field of Selector

\c ARPL r/m16,reg16              ; 63 /r                [286,PRIV]

\c{ARPL} expects its two word operands to be segment selectors. It
adjusts the \i\c{RPL} (requested privilege level - stored in the bottom
two bits of the selector) field of the destination (first) operand
to ensure that it is no less (i.e. no more privileged than) the \c{RPL}
field of the source operand. The zero flag is set if and only if a
change had to be made.


\S{insBOUND} \i\c{BOUND}: Check Array Index against Bounds

\c BOUND reg16,mem               ; o16 62 /r            [186]
\c BOUND reg32,mem               ; o32 62 /r            [386]

\c{BOUND} expects its second operand to point to an area of memory
containing two signed values of the same size as its first operand
(i.e. two words for the 16-bit form; two doublewords for the 32-bit
form). It performs two signed comparisons: if the value in the
register passed as its first operand is less than the first of the
in-memory values, or is greater than or equal to the second, it
throws a \c{BR} exception. Otherwise, it does nothing.


\S{insBSF} \i\c{BSF}, \i\c{BSR}: Bit Scan

\c BSF reg16,r/m16               ; o16 0F BC /r         [386]
\c BSF reg32,r/m32               ; o32 0F BC /r         [386]

\c BSR reg16,r/m16               ; o16 0F BD /r         [386]
\c BSR reg32,r/m32               ; o32 0F BD /r         [386]

\b \c{BSF} searches for the least significant set bit in its source
(second) operand, and if it finds one, stores the index in
its destination (first) operand. If no set bit is found, the
contents of the destination operand are undefined. If the source
operand is zero, the zero flag is set.

\b \c{BSR} performs the same function, but searches from the top
instead, so it finds the most significant set bit.

Bit indices are from 0 (least significant) to 15 or 31 (most
significant). The destination operand can only be a register.
The source operand can be a register or a memory location.


\S{insBSWAP} \i\c{BSWAP}: Byte Swap

\c BSWAP reg32                   ; o32 0F C8+r          [486]

\c{BSWAP} swaps the order of the four bytes of a 32-bit register:
bits 0-7 exchange places with bits 24-31, and bits 8-15 swap with
bits 16-23. There is no explicit 16-bit equivalent: to byte-swap
\c{AX}, \c{BX}, \c{CX} or \c{DX}, \c{XCHG} can be used. When \c{BSWAP}
is used with a 16-bit register, the result is undefined.


\S{insBT} \i\c{BT}, \i\c{BTC}, \i\c{BTR}, \i\c{BTS}: Bit Test

\c BT r/m16,reg16                ; o16 0F A3 /r         [386]
\c BT r/m32,reg32                ; o32 0F A3 /r         [386]
\c BT r/m16,imm8                 ; o16 0F BA /4 ib      [386]
\c BT r/m32,imm8                 ; o32 0F BA /4 ib      [386]

\c BTC r/m16,reg16               ; o16 0F BB /r         [386]
\c BTC r/m32,reg32               ; o32 0F BB /r         [386]
\c BTC r/m16,imm8                ; o16 0F BA /7 ib      [386]
\c BTC r/m32,imm8                ; o32 0F BA /7 ib      [386]

\c BTR r/m16,reg16               ; o16 0F B3 /r         [386]
\c BTR r/m32,reg32               ; o32 0F B3 /r         [386]
\c BTR r/m16,imm8                ; o16 0F BA /6 ib      [386]
\c BTR r/m32,imm8                ; o32 0F BA /6 ib      [386]

\c BTS r/m16,reg16               ; o16 0F AB /r         [386]
\c BTS r/m32,reg32               ; o32 0F AB /r         [386]
\c BTS r/m16,imm                 ; o16 0F BA /5 ib      [386]
\c BTS r/m32,imm                 ; o32 0F BA /5 ib      [386]

These instructions all test one bit of their first operand, whose
index is given by the second operand, and store the value of that
bit into the carry flag. Bit indices are from 0 (least significant)
to 15 or 31 (most significant).

In addition to storing the original value of the bit into the carry
flag, \c{BTR} also resets (clears) the bit in the operand itself.
\c{BTS} sets the bit, and \c{BTC} complements the bit. \c{BT} does
not modify its operands.

The destination can be a register or a memory location. The source can
be a register or an immediate value.

If the destination operand is a register, the bit offset should be
in the range 0-15 (for 16-bit operands) or 0-31 (for 32-bit operands).
An immediate value outside these ranges will be taken modulo 16/32
by the processor.

If the destination operand is a memory location, then an immediate
bit offset follows the same rules as for a register. If the bit offset
is in a register, then it can be anything within the signed range of
the register used (ie, for a 32-bit operand, it can be (-2^31) to (2^31 - 1)


\S{insCALL} \i\c{CALL}: Call Subroutine

\c CALL imm                      ; E8 rw/rd             [8086]
\c CALL imm:imm16                ; o16 9A iw iw         [8086]
\c CALL imm:imm32                ; o32 9A id iw         [386]
\c CALL FAR mem16                ; o16 FF /3            [8086]
\c CALL FAR mem32                ; o32 FF /3            [386]
\c CALL r/m16                    ; o16 FF /2            [8086]
\c CALL r/m32                    ; o32 FF /2            [386]

\c{CALL} calls a subroutine, by means of pushing the current
instruction pointer (\c{IP}) and optionally \c{CS} as well on the
stack, and then jumping to a given address.

\c{CS} is pushed as well as \c{IP} if and only if the call is a far
call, i.e. a destination segment address is specified in the
instruction. The forms involving two colon-separated arguments are
far calls; so are the \c{CALL FAR mem} forms.

The immediate \i{near call} takes one of two forms (\c{call imm16/imm32},
determined by the current segment size limit. For 16-bit operands,
you would use \c{CALL 0x1234}, and for 32-bit operands you would use
\c{CALL 0x12345678}. The value passed as an operand is a relative offset.

You can choose between the two immediate \i{far call} forms
(\c{CALL imm:imm}) by the use of the \c{WORD} and \c{DWORD} keywords:
\c{CALL WORD 0x1234:0x5678}) or \c{CALL DWORD 0x1234:0x56789abc}.

The \c{CALL FAR mem} forms execute a far call by loading the
destination address out of memory. The address loaded consists of 16
or 32 bits of offset (depending on the operand size), and 16 bits of
segment. The operand size may be overridden using \c{CALL WORD FAR
mem} or \c{CALL DWORD FAR mem}.

The \c{CALL r/m} forms execute a \i{near call} (within the same
segment), loading the destination address out of memory or out of a
register. The keyword \c{NEAR} may be specified, for clarity, in
these forms, but is not necessary. Again, operand size can be
overridden using \c{CALL WORD mem} or \c{CALL DWORD mem}.

As a convenience, NASM does not require you to call a far procedure
symbol by coding the cumbersome \c{CALL SEG routine:routine}, but
instead allows the easier synonym \c{CALL FAR routine}.

The \c{CALL r/m} forms given above are near calls; NASM will accept
the \c{NEAR} keyword (e.g. \c{CALL NEAR [address]}), even though it
is not strictly necessary.


\S{insCBW} \i\c{CBW}, \i\c{CWD}, \i\c{CDQ}, \i\c{CWDE}: Sign Extensions

\c CBW                           ; o16 98               [8086]
\c CWDE                          ; o32 98               [386]

\c CWD                           ; o16 99               [8086]
\c CDQ                           ; o32 99               [386]

All these instructions sign-extend a short value into a longer one,
by replicating the top bit of the original value to fill the
extended one.

\c{CBW} extends \c{AL} into \c{AX} by repeating the top bit of
\c{AL} in every bit of \c{AH}. \c{CWDE} extends \c{AX} into
\c{EAX}. \c{CWD} extends \c{AX} into \c{DX:AX} by repeating
the top bit of \c{AX} throughout \c{DX}, and \c{CDQ} extends
\c{EAX} into \c{EDX:EAX}.


\S{insCLC} \i\c{CLC}, \i\c{CLD}, \i\c{CLI}, \i\c{CLTS}: Clear Flags

\c CLC                           ; F8                   [8086]
\c CLD                           ; FC                   [8086]
\c CLI                           ; FA                   [8086]
\c CLTS                          ; 0F 06                [286,PRIV]

These instructions clear various flags. \c{CLC} clears the carry
flag; \c{CLD} clears the direction flag; \c{CLI} clears the
interrupt flag (thus disabling interrupts); and \c{CLTS} clears the
task-switched (\c{TS}) flag in \c{CR0}.

To set the carry, direction, or interrupt flags, use the \c{STC},
\c{STD} and \c{STI} instructions (\k{insSTC}). To invert the carry
flag, use \c{CMC} (\k{insCMC}).


\S{insCLFLUSH} \i\c{CLFLUSH}: Flush Cache Line

\c CLFLUSH mem                   ; 0F AE /7        [WILLAMETTE,SSE2]

\c{CLFLUSH} invalidates the cache line that contains the linear address
specified by the source operand from all levels of the processor cache
hierarchy (data and instruction). If, at any level of the cache
hierarchy, the line is inconsistent with memory (dirty) it is written
to memory before invalidation. The source operand points to a
byte-sized memory location.

Although \c{CLFLUSH} is flagged \c{SSE2} and above, it may not be
present on all processors which have \c{SSE2} support, and it may be
supported on other processors; the \c{CPUID} instruction (\k{insCPUID})
will return a bit which indicates support for the \c{CLFLUSH} instruction.


\S{insCMC} \i\c{CMC}: Complement Carry Flag

\c CMC                           ; F5                   [8086]

\c{CMC} changes the value of the carry flag: if it was 0, it sets it
to 1, and vice versa.


\S{insCMOVcc} \i\c{CMOVcc}: Conditional Move

\c CMOVcc reg16,r/m16            ; o16 0F 40+cc /r      [P6]
\c CMOVcc reg32,r/m32            ; o32 0F 40+cc /r      [P6]

\c{CMOV} moves its source (second) operand into its destination
(first) operand if the given condition code is satisfied; otherwise
it does nothing.

For a list of condition codes, see \k{iref-cc}.

Although the \c{CMOV} instructions are flagged \c{P6} and above, they
may not be supported by all Pentium Pro processors; the \c{CPUID}
instruction (\k{insCPUID}) will return a bit which indicates whether
conditional moves are supported.


\S{insCMP} \i\c{CMP}: Compare Integers

\c CMP r/m8,reg8                 ; 38 /r                [8086]
\c CMP r/m16,reg16               ; o16 39 /r            [8086]
\c CMP r/m32,reg32               ; o32 39 /r            [386]

\c CMP reg8,r/m8                 ; 3A /r                [8086]
\c CMP reg16,r/m16               ; o16 3B /r            [8086]
\c CMP reg32,r/m32               ; o32 3B /r            [386]

\c CMP r/m8,imm8                 ; 80 /7 ib             [8086]
\c CMP r/m16,imm16               ; o16 81 /7 iw         [8086]
\c CMP r/m32,imm32               ; o32 81 /7 id         [386]

\c CMP r/m16,imm8                ; o16 83 /7 ib         [8086]
\c CMP r/m32,imm8                ; o32 83 /7 ib         [386]

\c CMP AL,imm8                   ; 3C ib                [8086]
\c CMP AX,imm16                  ; o16 3D iw            [8086]
\c CMP EAX,imm32                 ; o32 3D id            [386]

\c{CMP} performs a `mental' subtraction of its second operand from
its first operand, and affects the flags as if the subtraction had
taken place, but does not store the result of the subtraction
anywhere.

In the forms with an 8-bit immediate second operand and a longer
first operand, the second operand is considered to be signed, and is
sign-extended to the length of the first operand. In these cases,
the \c{BYTE} qualifier is necessary to force NASM to generate this
form of the instruction.

The destination operand can be a register or a memory location. The
source can be a register, memory location or an immediate value of
the same size as the destination.


\S{insCMPccPD} \i\c{CMPccPD}: Packed Double-Precision FP Compare
\I\c{CMPEQPD} \I\c{CMPLTPD} \I\c{CMPLEPD} \I\c{CMPUNORDPD}
\I\c{CMPNEQPD} \I\c{CMPNLTPD} \I\c{CMPNLEPD} \I\c{CMPORDPD}

\c CMPPD xmm1,xmm2/mem128,imm8   ; 66 0F C2 /r ib  [WILLAMETTE,SSE2]

\c CMPEQPD xmm1,xmm2/mem128      ; 66 0F C2 /r 00  [WILLAMETTE,SSE2]
\c CMPLTPD xmm1,xmm2/mem128      ; 66 0F C2 /r 01  [WILLAMETTE,SSE2]
\c CMPLEPD xmm1,xmm2/mem128      ; 66 0F C2 /r 02  [WILLAMETTE,SSE2]
\c CMPUNORDPD xmm1,xmm2/mem128   ; 66 0F C2 /r 03  [WILLAMETTE,SSE2]
\c CMPNEQPD xmm1,xmm2/mem128     ; 66 0F C2 /r 04  [WILLAMETTE,SSE2]
\c CMPNLTPD xmm1,xmm2/mem128     ; 66 0F C2 /r 05  [WILLAMETTE,SSE2]
\c CMPNLEPD xmm1,xmm2/mem128     ; 66 0F C2 /r 06  [WILLAMETTE,SSE2]
\c CMPORDPD xmm1,xmm2/mem128     ; 66 0F C2 /r 07  [WILLAMETTE,SSE2]

The \c{CMPccPD} instructions compare the two packed double-precision
FP values in the source and destination operands, and returns the
result of the comparison in the destination register. The result of
each comparison is a quadword mask of all 1s (comparison true) or
all 0s (comparison false).

The destination is an \c{XMM} register. The source can be either an
\c{XMM} register or a 128-bit memory location.

The third operand is an 8-bit immediate value, of which the low 3
bits define the type of comparison. For ease of programming, the
8 two-operand pseudo-instructions are provided, with the third
operand already filled in. The \I{Condition Predicates}
\c{Condition Predicates} are:

\c EQ     0   Equal
\c LT     1   Less-than
\c LE     2   Less-than-or-equal
\c UNORD  3   Unordered
\c NE     4   Not-equal
\c NLT    5   Not-less-than
\c NLE    6   Not-less-than-or-equal
\c ORD    7   Ordered

For more details of the comparison predicates, and details of how
to emulate the "greater-than" equivalents, see \k{iref-SSE-cc}


\S{insCMPccPS} \i\c{CMPccPS}: Packed Single-Precision FP Compare
\I\c{CMPEQPS} \I\c{CMPLTPS} \I\c{CMPLEPS} \I\c{CMPUNORDPS}
\I\c{CMPNEQPS} \I\c{CMPNLTPS} \I\c{CMPNLEPS} \I\c{CMPORDPS}

\c CMPPS xmm1,xmm2/mem128,imm8   ; 0F C2 /r ib     [KATMAI,SSE]

\c CMPEQPS xmm1,xmm2/mem128      ; 0F C2 /r 00     [KATMAI,SSE]
\c CMPLTPS xmm1,xmm2/mem128      ; 0F C2 /r 01     [KATMAI,SSE]
\c CMPLEPS xmm1,xmm2/mem128      ; 0F C2 /r 02     [KATMAI,SSE]
\c CMPUNORDPS xmm1,xmm2/mem128   ; 0F C2 /r 03     [KATMAI,SSE]
\c CMPNEQPS xmm1,xmm2/mem128     ; 0F C2 /r 04     [KATMAI,SSE]
\c CMPNLTPS xmm1,xmm2/mem128     ; 0F C2 /r 05     [KATMAI,SSE]
\c CMPNLEPS xmm1,xmm2/mem128     ; 0F C2 /r 06     [KATMAI,SSE]
\c CMPORDPS xmm1,xmm2/mem128     ; 0F C2 /r 07     [KATMAI,SSE]

The \c{CMPccPS} instructions compare the two packed single-precision
FP values in the source and destination operands, and returns the
result of the comparison in the destination register. The result of
each comparison is a doubleword mask of all 1s (comparison true) or
all 0s (comparison false).

The destination is an \c{XMM} register. The source can be either an
\c{XMM} register or a 128-bit memory location.

The third operand is an 8-bit immediate value, of which the low 3
bits define the type of comparison. For ease of programming, the
8 two-operand pseudo-instructions are provided, with the third
operand already filled in. The \I{Condition Predicates}
\c{Condition Predicates} are:

\c EQ     0   Equal
\c LT     1   Less-than
\c LE     2   Less-than-or-equal
\c UNORD  3   Unordered
\c NE     4   Not-equal
\c NLT    5   Not-less-than
\c NLE    6   Not-less-than-or-equal
\c ORD    7   Ordered

For more details of the comparison predicates, and details of how
to emulate the "greater-than" equivalents, see \k{iref-SSE-cc}


\S{insCMPSB} \i\c{CMPSB}, \i\c{CMPSW}, \i\c{CMPSD}: Compare Strings

\c CMPSB                         ; A6                   [8086]
\c CMPSW                         ; o16 A7               [8086]
\c CMPSD                         ; o32 A7               [386]

\c{CMPSB} compares the byte at \c{[DS:SI]} or \c{[DS:ESI]} with the
byte at \c{[ES:DI]} or \c{[ES:EDI]}, and sets the flags accordingly.
It then increments or decrements (depending on the direction flag:
increments if the flag is clear, decrements if it is set) \c{SI} and
\c{DI} (or \c{ESI} and \c{EDI}).

The registers used are \c{SI} and \c{DI} if the address size is 16
bits, and \c{ESI} and \c{EDI} if it is 32 bits. If you need to use
an address size not equal to the current \c{BITS} setting, you can
use an explicit \i\c{a16} or \i\c{a32} prefix.

The segment register used to load from \c{[SI]} or \c{[ESI]} can be
overridden by using a segment register name as a prefix (for
example, \c{ES CMPSB}). The use of \c{ES} for the load from \c{[DI]}
or \c{[EDI]} cannot be overridden.

\c{CMPSW} and \c{CMPSD} work in the same way, but they compare a
word or a doubleword instead of a byte, and increment or decrement
the addressing registers by 2 or 4 instead of 1.

The \c{REPE} and \c{REPNE} prefixes (equivalently, \c{REPZ} and
\c{REPNZ}) may be used to repeat the instruction up to \c{CX} (or
\c{ECX} - again, the address size chooses which) times until the
first unequal or equal byte is found.


\S{insCMPccSD} \i\c{CMPccSD}: Scalar Double-Precision FP Compare
\I\c{CMPEQSD} \I\c{CMPLTSD} \I\c{CMPLESD} \I\c{CMPUNORDSD}
\I\c{CMPNEQSD} \I\c{CMPNLTSD} \I\c{CMPNLESD} \I\c{CMPORDSD}

\c CMPSD xmm1,xmm2/mem64,imm8    ; F2 0F C2 /r ib  [WILLAMETTE,SSE2]

\c CMPEQSD xmm1,xmm2/mem64       ; F2 0F C2 /r 00  [WILLAMETTE,SSE2]
\c CMPLTSD xmm1,xmm2/mem64       ; F2 0F C2 /r 01  [WILLAMETTE,SSE2]
\c CMPLESD xmm1,xmm2/mem64       ; F2 0F C2 /r 02  [WILLAMETTE,SSE2]
\c CMPUNORDSD xmm1,xmm2/mem64    ; F2 0F C2 /r 03  [WILLAMETTE,SSE2]
\c CMPNEQSD xmm1,xmm2/mem64      ; F2 0F C2 /r 04  [WILLAMETTE,SSE2]
\c CMPNLTSD xmm1,xmm2/mem64      ; F2 0F C2 /r 05  [WILLAMETTE,SSE2]
\c CMPNLESD xmm1,xmm2/mem64      ; F2 0F C2 /r 06  [WILLAMETTE,SSE2]
\c CMPORDSD xmm1,xmm2/mem64      ; F2 0F C2 /r 07  [WILLAMETTE,SSE2]

The \c{CMPccSD} instructions compare the low-order double-precision
FP values in the source and destination operands, and returns the
result of the comparison in the destination register. The result of
each comparison is a quadword mask of all 1s (comparison true) or
all 0s (comparison false).

The destination is an \c{XMM} register. The source can be either an
\c{XMM} register or a 128-bit memory location.

The third operand is an 8-bit immediate value, of which the low 3
bits define the type of comparison. For ease of programming, the
8 two-operand pseudo-instructions are provided, with the third
operand already filled in. The \I{Condition Predicates}
\c{Condition Predicates} are:

\c EQ     0   Equal
\c LT     1   Less-than
\c LE     2   Less-than-or-equal
\c UNORD  3   Unordered
\c NE     4   Not-equal
\c NLT    5   Not-less-than
\c NLE    6   Not-less-than-or-equal
\c ORD    7   Ordered

For more details of the comparison predicates, and details of how
to emulate the "greater-than" equivalents, see \k{iref-SSE-cc}


\S{insCMPccSS} \i\c{CMPccSS}: Scalar Single-Precision FP Compare
\I\c{CMPEQSS} \I\c{CMPLTSS} \I\c{CMPLESS} \I\c{CMPUNORDSS}
\I\c{CMPNEQSS} \I\c{CMPNLTSS} \I\c{CMPNLESS} \I\c{CMPORDSS}

\c CMPSS xmm1,xmm2/mem32,imm8    ; F3 0F C2 /r ib  [KATMAI,SSE]

\c CMPEQSS xmm1,xmm2/mem32       ; F3 0F C2 /r 00  [KATMAI,SSE]
\c CMPLTSS xmm1,xmm2/mem32       ; F3 0F C2 /r 01  [KATMAI,SSE]
\c CMPLESS xmm1,xmm2/mem32       ; F3 0F C2 /r 02  [KATMAI,SSE]
\c CMPUNORDSS xmm1,xmm2/mem32    ; F3 0F C2 /r 03  [KATMAI,SSE]
\c CMPNEQSS xmm1,xmm2/mem32      ; F3 0F C2 /r 04  [KATMAI,SSE]
\c CMPNLTSS xmm1,xmm2/mem32      ; F3 0F C2 /r 05  [KATMAI,SSE]
\c CMPNLESS xmm1,xmm2/mem32      ; F3 0F C2 /r 06  [KATMAI,SSE]
\c CMPORDSS xmm1,xmm2/mem32      ; F3 0F C2 /r 07  [KATMAI,SSE]

The \c{CMPccSS} instructions compare the low-order single-precision
FP values in the source and destination operands, and returns the
result of the comparison in the destination register. The result of
each comparison is a doubleword mask of all 1s (comparison true) or
all 0s (comparison false).

The destination is an \c{XMM} register. The source can be either an
\c{XMM} register or a 128-bit memory location.

The third operand is an 8-bit immediate value, of which the low 3
bits define the type of comparison. For ease of programming, the
8 two-operand pseudo-instructions are provided, with the third
operand already filled in. The \I{Condition Predicates}
\c{Condition Predicates} are:

\c EQ     0   Equal
\c LT     1   Less-than
\c LE     2   Less-than-or-equal
\c UNORD  3   Unordered
\c NE     4   Not-equal
\c NLT    5   Not-less-than
\c NLE    6   Not-less-than-or-equal
\c ORD    7   Ordered

For more details of the comparison predicates, and details of how
to emulate the "greater-than" equivalents, see \k{iref-SSE-cc}


\S{insCMPXCHG} \i\c{CMPXCHG}, \i\c{CMPXCHG486}: Compare and Exchange

\c CMPXCHG r/m8,reg8             ; 0F B0 /r             [PENT]
\c CMPXCHG r/m16,reg16           ; o16 0F B1 /r         [PENT]
\c CMPXCHG r/m32,reg32           ; o32 0F B1 /r         [PENT]

\c CMPXCHG486 r/m8,reg8          ; 0F A6 /r             [486,UNDOC]
\c CMPXCHG486 r/m16,reg16        ; o16 0F A7 /r         [486,UNDOC]
\c CMPXCHG486 r/m32,reg32        ; o32 0F A7 /r         [486,UNDOC]

These two instructions perform exactly the same operation; however,
apparently some (not all) 486 processors support it under a
non-standard opcode, so NASM provides the undocumented
\c{CMPXCHG486} form to generate the non-standard opcode.

\c{CMPXCHG} compares its destination (first) operand to the value in
\c{AL}, \c{AX} or \c{EAX} (depending on the operand size of the
instruction). If they are equal, it copies its source (second)
operand into the destination and sets the zero flag. Otherwise, it
clears the zero flag and copies the destination register to AL, AX or EAX.

The destination can be either a register or a memory location. The
source is a register.

\c{CMPXCHG} is intended to be used for atomic operations in
multitasking or multiprocessor environments. To safely update a
value in shared memory, for example, you might load the value into
\c{EAX}, load the updated value into \c{EBX}, and then execute the
instruction \c{LOCK CMPXCHG [value],EBX}. If \c{value} has not
changed since being loaded, it is updated with your desired new
value, and the zero flag is set to let you know it has worked. (The
\c{LOCK} prefix prevents another processor doing anything in the
middle of this operation: it guarantees atomicity.) However, if
another processor has modified the value in between your load and
your attempted store, the store does not happen, and you are
notified of the failure by a cleared zero flag, so you can go round
and try again.


\S{insCMPXCHG8B} \i\c{CMPXCHG8B}: Compare and Exchange Eight Bytes

\c CMPXCHG8B mem                 ; 0F C7 /1             [PENT]

This is a larger and more unwieldy version of \c{CMPXCHG}: it
compares the 64-bit (eight-byte) value stored at \c{[mem]} with the
value in \c{EDX:EAX}. If they are equal, it sets the zero flag and
stores \c{ECX:EBX} into the memory area. If they are unequal, it
clears the zero flag and stores the memory contents into \c{EDX:EAX}.

\c{CMPXCHG8B} can be used with the \c{LOCK} prefix, to allow atomic
execution. This is useful in multi-processor and multi-tasking
environments.


\S{insCOMISD} \i\c{COMISD}: Scalar Ordered Double-Precision FP Compare and Set EFLAGS

\c COMISD xmm1,xmm2/mem64        ; 66 0F 2F /r     [WILLAMETTE,SSE2]

\c{COMISD} compares the low-order double-precision FP value in the
two source operands. ZF, PF and CF are set according to the result.
OF, AF and AF are cleared. The unordered result is returned if either
source is a NaN (QNaN or SNaN).

The destination operand is an \c{XMM} register. The source can be either
an \c{XMM} register or a memory location.

The flags are set according to the following rules:

\c    Result          Flags        Values

\c    UNORDERED:      ZF,PF,CF <-- 111;
\c    GREATER_THAN:   ZF,PF,CF <-- 000;
\c    LESS_THAN:      ZF,PF,CF <-- 001;
\c    EQUAL:          ZF,PF,CF <-- 100;


\S{insCOMISS} \i\c{COMISS}: Scalar Ordered Single-Precision FP Compare and Set EFLAGS

\c COMISS xmm1,xmm2/mem32        ; 66 0F 2F /r     [KATMAI,SSE]

\c{COMISS} compares the low-order single-precision FP value in the
two source operands. ZF, PF and CF are set according to the result.
OF, AF and AF are cleared. The unordered result is returned if either
source is a NaN (QNaN or SNaN).

The destination operand is an \c{XMM} register. The source can be either
an \c{XMM} register or a memory location.

The flags are set according to the following rules:

\c    Result          Flags        Values

\c    UNORDERED:      ZF,PF,CF <-- 111;
\c    GREATER_THAN:   ZF,PF,CF <-- 000;
\c    LESS_THAN:      ZF,PF,CF <-- 001;
\c    EQUAL:          ZF,PF,CF <-- 100;


\S{insCPUID} \i\c{CPUID}: Get CPU Identification Code

\c CPUID                         ; 0F A2                [PENT]

\c{CPUID} returns various information about the processor it is
being executed on. It fills the four registers \c{EAX}, \c{EBX},
\c{ECX} and \c{EDX} with information, which varies depending on the
input contents of \c{EAX}.

\c{CPUID} also acts as a barrier to serialize instruction execution:
executing the \c{CPUID} instruction guarantees that all the effects
(memory modification, flag modification, register modification) of
previous instructions have been completed before the next
instruction gets fetched.

The information returned is as follows:

\b If \c{EAX} is zero on input, \c{EAX} on output holds the maximum
acceptable input value of \c{EAX}, and \c{EBX:EDX:ECX} contain the
string \c{"GenuineIntel"} (or not, if you have a clone processor).
That is to say, \c{EBX} contains \c{"Genu"} (in NASM's own sense of
character constants, described in \k{chrconst}), \c{EDX} contains
\c{"ineI"} and \c{ECX} contains \c{"ntel"}.

\b If \c{EAX} is one on input, \c{EAX} on output contains version
information about the processor, and \c{EDX} contains a set of
feature flags, showing the presence and absence of various features.
For example, bit 8 is set if the \c{CMPXCHG8B} instruction
(\k{insCMPXCHG8B}) is supported, bit 15 is set if the conditional
move instructions (\k{insCMOVcc} and \k{insFCMOVB}) are supported,
and bit 23 is set if \c{MMX} instructions are supported.

\b If \c{EAX} is two on input, \c{EAX}, \c{EBX}, \c{ECX} and \c{EDX}
all contain information about caches and TLBs (Translation Lookahead
Buffers).

For more information on the data returned from \c{CPUID}, see the
documentation from Intel and other processor manufacturers.


\S{insCVTDQ2PD} \i\c{CVTDQ2PD}:
Packed Signed INT32 to Packed Double-Precision FP Conversion

\c CVTDQ2PD xmm1,xmm2/mem64      ; F3 0F E6 /r     [WILLAMETTE,SSE2]

\c{CVTDQ2PD} converts two packed signed doublewords from the source
operand to two packed double-precision FP values in the destination
operand.

The destination operand is an \c{XMM} register. The source can be
either an \c{XMM} register or a 64-bit memory location. If the
source is a register, the packed integers are in the low quadword.


\S{insCVTDQ2PS} \i\c{CVTDQ2PS}:
Packed Signed INT32 to Packed Single-Precision FP Conversion

\c CVTDQ2PS xmm1,xmm2/mem128     ; 0F 5B /r        [WILLAMETTE,SSE2]

\c{CVTDQ2PS} converts four packed signed doublewords from the source
operand to four packed single-precision FP values in the destination
operand.

The destination operand is an \c{XMM} register. The source can be
either an \c{XMM} register or a 128-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTPD2DQ} \i\c{CVTPD2DQ}:
Packed Double-Precision FP to Packed Signed INT32 Conversion

\c CVTPD2DQ xmm1,xmm2/mem128     ; F2 0F E6 /r     [WILLAMETTE,SSE2]

\c{CVTPD2DQ} converts two packed double-precision FP values from the
source operand to two packed signed doublewords in the low quadword
of the destination operand. The high quadword of the destination is
set to all 0s.

The destination operand is an \c{XMM} register. The source can be
either an \c{XMM} register or a 128-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTPD2PI} \i\c{CVTPD2PI}:
Packed Double-Precision FP to Packed Signed INT32 Conversion

\c CVTPD2PI mm,xmm/mem128        ; 66 0F 2D /r     [WILLAMETTE,SSE2]

\c{CVTPD2PI} converts two packed double-precision FP values from the
source operand to two packed signed doublewords in the destination
operand.

The destination operand is an \c{MMX} register. The source can be
either an \c{XMM} register or a 128-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTPD2PS} \i\c{CVTPD2PS}:
Packed Double-Precision FP to Packed Single-Precision FP Conversion

\c CVTPD2PS xmm1,xmm2/mem128     ; 66 0F 5A /r     [WILLAMETTE,SSE2]

\c{CVTPD2PS} converts two packed double-precision FP values from the
source operand to two packed single-precision FP values in the low
quadword of the destination operand. The high quadword of the
destination is set to all 0s.

The destination operand is an \c{XMM} register. The source can be
either an \c{XMM} register or a 128-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTPI2PD} \i\c{CVTPI2PD}:
Packed Signed INT32 to Packed Double-Precision FP Conversion

\c CVTPI2PD xmm,mm/mem64         ; 66 0F 2A /r     [WILLAMETTE,SSE2]

\c{CVTPI2PD} converts two packed signed doublewords from the source
operand to two packed double-precision FP values in the destination
operand.

The destination operand is an \c{XMM} register. The source can be
either an \c{MMX} register or a 64-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTPI2PS} \i\c{CVTPI2PS}:
Packed Signed INT32 to Packed Single-FP Conversion

\c CVTPI2PS xmm,mm/mem64         ; 0F 2A /r        [KATMAI,SSE]

\c{CVTPI2PS} converts two packed signed doublewords from the source
operand to two packed single-precision FP values in the low quadword
of the destination operand. The high quadword of the destination
remains unchanged.

The destination operand is an \c{XMM} register. The source can be
either an \c{MMX} register or a 64-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTPS2DQ} \i\c{CVTPS2DQ}:
Packed Single-Precision FP to Packed Signed INT32 Conversion

\c CVTPS2DQ xmm1,xmm2/mem128     ; 66 0F 5B /r     [WILLAMETTE,SSE2]

\c{CVTPS2DQ} converts four packed single-precision FP values from the
source operand to four packed signed doublewords in the destination operand.

The destination operand is an \c{XMM} register. The source can be
either an \c{XMM} register or a 128-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTPS2PD} \i\c{CVTPS2PD}:
Packed Single-Precision FP to Packed Double-Precision FP Conversion

\c CVTPS2PD xmm1,xmm2/mem64      ; 0F 5A /r        [WILLAMETTE,SSE2]

\c{CVTPS2PD} converts two packed single-precision FP values from the
source operand to two packed double-precision FP values in the destination
operand.

The destination operand is an \c{XMM} register. The source can be
either an \c{XMM} register or a 64-bit memory location. If the source
is a register, the input values are in the low quadword.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTPS2PI} \i\c{CVTPS2PI}:
Packed Single-Precision FP to Packed Signed INT32 Conversion

\c CVTPS2PI mm,xmm/mem64         ; 0F 2D /r        [KATMAI,SSE]

\c{CVTPS2PI} converts two packed single-precision FP values from
the source operand to two packed signed doublewords in the destination
operand.

The destination operand is an \c{MMX} register. The source can be
either an \c{XMM} register or a 64-bit memory location. If the
source is a register, the input values are in the low quadword.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTSD2SI} \i\c{CVTSD2SI}:
Scalar Double-Precision FP to Signed INT32 Conversion

\c CVTSD2SI reg32,xmm/mem64      ; F2 0F 2D /r     [WILLAMETTE,SSE2]

\c{CVTSD2SI} converts a double-precision FP value from the source
operand to a signed doubleword in the destination operand.

The destination operand is a general purpose register. The source can be
either an \c{XMM} register or a 64-bit memory location. If the
source is a register, the input value is in the low quadword.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTSD2SS} \i\c{CVTSD2SS}:
Scalar Double-Precision FP to Scalar Single-Precision FP Conversion

\c CVTSD2SS xmm1,xmm2/mem64      ; F2 0F 5A /r     [KATMAI,SSE]

\c{CVTSD2SS} converts a double-precision FP value from the source
operand to a single-precision FP value in the low doubleword of the
destination operand. The upper 3 doublewords are left unchanged.

The destination operand is an \c{XMM} register. The source can be
either an \c{XMM} register or a 64-bit memory location. If the
source is a register, the input value is in the low quadword.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTSI2SD} \i\c{CVTSI2SD}:
Signed INT32 to Scalar Double-Precision FP Conversion

\c CVTSI2SD xmm,r/m32            ; F2 0F 2A /r     [WILLAMETTE,SSE2]

\c{CVTSI2SD} converts a signed doubleword from the source operand to
a double-precision FP value in the low quadword of the destination
operand. The high quadword is left unchanged.

The destination operand is an \c{XMM} register. The source can be either
a general purpose register or a 32-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTSI2SS} \i\c{CVTSI2SS}:
Signed INT32 to Scalar Single-Precision FP Conversion

\c CVTSI2SS xmm,r/m32            ; F3 0F 2A /r     [KATMAI,SSE]

\c{CVTSI2SS} converts a signed doubleword from the source operand to a
single-precision FP value in the low doubleword of the destination operand.
The upper 3 doublewords are left unchanged.

The destination operand is an \c{XMM} register. The source can be either
a general purpose register or a 32-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTSS2SD} \i\c{CVTSS2SD}:
Scalar Single-Precision FP to Scalar Double-Precision FP Conversion

\c CVTSS2SD xmm1,xmm2/mem32      ; F3 0F 5A /r     [WILLAMETTE,SSE2]

\c{CVTSS2SD} converts a single-precision FP value from the source operand
to a double-precision FP value in the low quadword of the destination
operand. The upper quadword is left unchanged.

The destination operand is an \c{XMM} register. The source can be either
an \c{XMM} register or a 32-bit memory location. If the source is a
register, the input value is contained in the low doubleword.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTSS2SI} \i\c{CVTSS2SI}:
Scalar Single-Precision FP to Signed INT32 Conversion

\c CVTSS2SI reg32,xmm/mem32      ; F3 0F 2D /r     [KATMAI,SSE]

\c{CVTSS2SI} converts a single-precision FP value from the source
operand to a signed doubleword in the destination operand.

The destination operand is a general purpose register. The source can be
either an \c{XMM} register or a 32-bit memory location. If the
source is a register, the input value is in the low doubleword.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTTPD2DQ} \i\c{CVTTPD2DQ}:
Packed Double-Precision FP to Packed Signed INT32 Conversion with Truncation

\c CVTTPD2DQ xmm1,xmm2/mem128    ; 66 0F E6 /r     [WILLAMETTE,SSE2]

\c{CVTTPD2DQ} converts two packed double-precision FP values in the source
operand to two packed single-precision FP values in the destination operand.
If the result is inexact, it is truncated (rounded toward zero). The high
quadword is set to all 0s.

The destination operand is an \c{XMM} register. The source can be
either an \c{XMM} register or a 128-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTTPD2PI} \i\c{CVTTPD2PI}:
Packed Double-Precision FP to Packed Signed INT32 Conversion with Truncation

\c CVTTPD2PI mm,xmm/mem128        ; 66 0F 2C /r     [WILLAMETTE,SSE2]

\c{CVTTPD2PI} converts two packed double-precision FP values in the source
operand to two packed single-precision FP values in the destination operand.
If the result is inexact, it is truncated (rounded toward zero).

The destination operand is an \c{MMX} register. The source can be
either an \c{XMM} register or a 128-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTTPS2DQ} \i\c{CVTTPS2DQ}:
Packed Single-Precision FP to Packed Signed INT32 Conversion with Truncation

\c CVTTPS2DQ xmm1,xmm2/mem128    ; F3 0F 5B /r     [WILLAMETTE,SSE2]

\c{CVTTPS2DQ} converts four packed single-precision FP values in the source
operand to four packed signed doublewords in the destination operand.
If the result is inexact, it is truncated (rounded toward zero).

The destination operand is an \c{XMM} register. The source can be
either an \c{XMM} register or a 128-bit memory location.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTTPS2PI} \i\c{CVTTPS2PI}:
Packed Single-Precision FP to Packed Signed INT32 Conversion with Truncation

\c CVTTPS2PI mm,xmm/mem64         ; 0F 2C /r       [KATMAI,SSE]

\c{CVTTPS2PI} converts two packed single-precision FP values in the source
operand to two packed signed doublewords in the destination operand.
If the result is inexact, it is truncated (rounded toward zero). If
the source is a register, the input values are in the low quadword.

The destination operand is an \c{MMX} register. The source can be
either an \c{XMM} register or a 64-bit memory location. If the source
is a register, the input value is in the low quadword.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTTSD2SI} \i\c{CVTTSD2SI}:
Scalar Double-Precision FP to Signed INT32 Conversion with Truncation

\c CVTTSD2SI reg32,xmm/mem64      ; F2 0F 2C /r    [WILLAMETTE,SSE2]

\c{CVTTSD2SI} converts a double-precision FP value in the source operand
to a signed doubleword in the destination operand. If the result is
inexact, it is truncated (rounded toward zero).

The destination operand is a general purpose register. The source can be
either an \c{XMM} register or a 64-bit memory location. If the source is a
register, the input value is in the low quadword.

For more details of this instruction, see the Intel Processor manuals.


\S{insCVTTSS2SI} \i\c{CVTTSS2SI}:
Scalar Single-Precision FP to Signed INT32 Conversion with Truncation

\c CVTTSD2SI reg32,xmm/mem32      ; F3 0F 2C /r    [KATMAI,SSE]

\c{CVTTSS2SI} converts a single-precision FP value in the source operand
to a signed doubleword in the destination operand. If the result is
inexact, it is truncated (rounded toward zero).

The destination operand is a general purpose register. The source can be
either an \c{XMM} register or a 32-bit memory location. If the source is a
register, the input value is in the low doubleword.

For more details of this instruction, see the Intel Processor manuals.


\S{insDAA} \i\c{DAA}, \i\c{DAS}: Decimal Adjustments

\c DAA                           ; 27                   [8086]
\c DAS                           ; 2F                   [8086]

These instructions are used in conjunction with the add and subtract
instructions to perform binary-coded decimal arithmetic in
\e{packed} (one BCD digit per nibble) form. For the unpacked
equivalents, see \k{insAAA}.

\c{DAA} should be used after a one-byte \c{ADD} instruction whose
destination was the \c{AL} register: by means of examining the value
in the \c{AL} and also the auxiliary carry flag \c{AF}, it
determines whether either digit of the addition has overflowed, and
adjusts it (and sets the carry and auxiliary-carry flags) if so. You
can add long BCD strings together by doing \c{ADD}/\c{DAA} on the
low two digits, then doing \c{ADC}/\c{DAA} on each subsequent pair
of digits.

\c{DAS} works similarly to \c{DAA}, but is for use after \c{SUB}
instructions rather than \c{ADD}.


\S{insDEC} \i\c{DEC}: Decrement Integer

\c DEC reg16                     ; o16 48+r             [8086]
\c DEC reg32                     ; o32 48+r             [386]
\c DEC r/m8                      ; FE /1                [8086]
\c DEC r/m16                     ; o16 FF /1            [8086]
\c DEC r/m32                     ; o32 FF /1            [386]

\c{DEC} subtracts 1 from its operand. It does \e{not} affect the
carry flag: to affect the carry flag, use \c{SUB something,1} (see
\k{insSUB}). \c{DEC} affects all the other flags according to the result.

This instruction can be used with a \c{LOCK} prefix to allow atomic
execution.

See also \c{INC} (\k{insINC}).


\S{insDIV} \i\c{DIV}: Unsigned Integer Divide

\c DIV r/m8                      ; F6 /6                [8086]
\c DIV r/m16                     ; o16 F7 /6            [8086]
\c DIV r/m32                     ; o32 F7 /6            [386]

\c{DIV} performs unsigned integer division. The explicit operand
provided is the divisor; the dividend and destination operands are
implicit, in the following way:

\b For \c{DIV r/m8}, \c{AX} is divided by the given operand; the
quotient is stored in \c{AL} and the remainder in \c{AH}.

\b For \c{DIV r/m16}, \c{DX:AX} is divided by the given operand; the
quotient is stored in \c{AX} and the remainder in \c{DX}.

\b For \c{DIV r/m32}, \c{EDX:EAX} is divided by the given operand;
the quotient is stored in \c{EAX} and the remainder in \c{EDX}.

Signed integer division is performed by the \c{IDIV} instruction:
see \k{insIDIV}.


\S{insDIVPD} \i\c{DIVPD}: Packed Double-Precision FP Divide

\c DIVPD xmm1,xmm2/mem128        ; 66 0F 5E /r     [WILLAMETTE,SSE2]

\c{DIVPD} divides the two packed double-precision FP values in
the destination operand by the two packed double-precision FP
values in the source operand, and stores the packed double-precision
results in the destination register.

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 128-bit memory location.

\c    dst[0-63]   := dst[0-63]   / src[0-63],
\c    dst[64-127] := dst[64-127] / src[64-127].


\S{insDIVPS} \i\c{DIVPS}: Packed Single-Precision FP Divide

\c DIVPS xmm1,xmm2/mem128        ; 0F 5E /r        [KATMAI,SSE]

\c{DIVPS} divides the four packed single-precision FP values in
the destination operand by the four packed single-precision FP
values in the source operand, and stores the packed single-precision
results in the destination register.

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 128-bit memory location.

\c    dst[0-31]   := dst[0-31]   / src[0-31],
\c    dst[32-63]  := dst[32-63]  / src[32-63],
\c    dst[64-95]  := dst[64-95]  / src[64-95],
\c    dst[96-127] := dst[96-127] / src[96-127].


\S{insDIVSD} \i\c{DIVSD}: Scalar Double-Precision FP Divide

\c DIVSD xmm1,xmm2/mem64         ; F2 0F 5E /r     [WILLAMETTE,SSE2]

\c{DIVSD} divides the low-order double-precision FP value in the
destination operand by the low-order double-precision FP value in
the source operand, and stores the double-precision result in the
destination register.

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 64-bit memory location.

\c    dst[0-63]   := dst[0-63] / src[0-63],
\c    dst[64-127] remains unchanged.


\S{insDIVSS} \i\c{DIVSS}: Scalar Single-Precision FP Divide

\c DIVSS xmm1,xmm2/mem32         ; F3 0F 5E /r     [KATMAI,SSE]

\c{DIVSS} divides the low-order single-precision FP value in the
destination operand by the low-order single-precision FP value in
the source operand, and stores the single-precision result in the
destination register.

The destination is an \c{XMM} register. The source operand can be
either an \c{XMM} register or a 32-bit memory location.

\c    dst[0-31]   := dst[0-31] / src[0-31],
\c    dst[32-127] remains unchanged.


\S{insEMMS} \i\c{EMMS}: Empty MMX State

\c EMMS                          ; 0F 77                [PENT,MMX]

\c{EMMS} sets the FPU tag word (marking which floating-point registers
are available) to all ones, meaning all registers are available for
the FPU to use. It should be used after executing \c{MMX} instructions
and before executing any subsequent floating-point operations.


\S{insENTER} \i\c{ENTER}: Create Stack Frame

\c ENTER imm,imm                 ; C8 iw ib             [186]

\c{ENTER} constructs a \i\c{stack frame} for a high-level language
procedure call. The first operand (the \c{iw} in the opcode
definition above refers to the first operand) gives the amount of
stack space to allocate for local variables; the second (the \c{ib}
above) gives the nesting level of the procedure (for languages like
Pascal, with nested procedures).

The function of \c{ENTER}, with a nesting level of zero, is
equivalent to

\c           PUSH EBP            ; or PUSH BP         in 16 bits
\c           MOV EBP,ESP         ; or MOV BP,SP       in 16 bits
\c           SUB ESP,operand1    ; or SUB SP,operand1 in 16 bits

This creates a stack frame with the procedure parameters accessible
upwards from \c{EBP}, and local variables accessible downwards from
\c{EBP}.

With a nesting level of one, the stack frame created is 4 (or 2)
bytes bigger, and the value of the final frame pointer \c{EBP} is
accessible in memory at \c{[EBP-4]}.

This allows \c{ENTER}, when called with a nesting level of two, to
look at the stack frame described by the \e{previous} value of
\c{EBP}, find the frame pointer at offset -4 from that, and push it
along with its new frame pointer, so that when a level-two procedure
is called from within a level-one procedure, \c{[EBP-4]} holds the
frame pointer of the most recent level-one procedure call and
\c{[EBP-8]} holds that of the most recent level-two call. And so on,
for nesting levels up to 31.

Stack frames created by \c{ENTER} can be destroyed by the \c{LEAVE}
instruction: see \k{insLEAVE}.


\S{insF2XM1} \i\c{F2XM1}: Calculate 2**X-1

\c F2XM1                         ; D9 F0                [8086,FPU]

\c{F2XM1} raises 2 to the power of \c{ST0}, subtracts one, and
stores the result back into \c{ST0}. The initial contents of \c{ST0}
must be a number in the range -1.0 to +1.0.


\S{insFABS} \i\c{FABS}: Floating-Point Absolute Value

\c FABS                          ; D9 E1                [8086,FPU]

\c{FABS} computes the absolute value of \c{ST0},by clearing the sign
bit, and stores the result back in \c{ST0}.


\S{insFADD} \i\c{FADD}, \i\c{FADDP}: Floating-Point Addition

\c FADD mem32                    ; D8 /0                [8086,FPU]
\c FADD mem64                    ; DC /0                [8086,FPU]

\c FADD fpureg                   ; D8 C0+r              [8086,FPU]
\c FADD ST0,fpureg               ; D8 C0+r              [8086,FPU]

\c FADD TO fpureg                ; DC C0+r              [8086,FPU]
\c FADD fpureg,ST0               ; DC C0+r              [8086,FPU]

\c FADDP fpureg                  ; DE C0+r              [8086,FPU]
\c FADDP fpureg,ST0              ; DE C0+r              [8086,FPU]

\b \c{FADD}, given one operand, adds the operand to \c{ST0} and stores
the result back in \c{ST0}. If the operand has the \c{TO} modifier,
the result is stored in the register given rather than in \c{ST0}.

\b \c{FADDP} performs the same function as \c{FADD TO}, but pops the
register stack after storing the result.

The given two-operand forms are synonyms for the one-operand forms.

To add an integer value to \c{ST0}, use the c{FIADD} instruction
(\k{insFIADD})


\S{insFBLD} \i\c{FBLD}, \i\c{FBSTP}: BCD Floating-Point Load and Store

\c FBLD mem80                    ; DF /4                [8086,FPU]
\c FBSTP mem80                   ; DF /6                [8086,FPU]

\c{FBLD} loads an 80-bit (ten-byte) packed binary-coded decimal
number from the given memory address, converts it to a real, and
pushes it on the register stack. \c{FBSTP} stores the value of
\c{ST0}, in packed BCD, at the given address and then pops the
register stack.


\S{insFCHS} \i\c{FCHS}: Floating-Point Change Sign

\c FCHS                          ; D9 E0                [8086,FPU]

\c{FCHS} negates the number in \c{ST0}, by inverting the sign bit:
negative numbers become positive, and vice versa.


\S{insFCLEX} \i\c{FCLEX}, \c{FNCLEX}: Clear Floating-Point Exceptions

\c FCLEX                         ; 9B DB E2             [8086,FPU]
\c FNCLEX                        ; DB E2                [8086,FPU]

\c{FCLEX} clears any floating-point exceptions which may be pending.
\c{FNCLEX} does the same thing but doesn't wait for previous
floating-point operations (including the \e{handling} of pending
exceptions) to finish first.


\S{insFCMOVB} \i\c{FCMOVcc}: Floating-Point Conditional Move

\c FCMOVB fpureg                 ; DA C0+r              [P6,FPU]
\c FCMOVB ST0,fpureg             ; DA C0+r              [P6,FPU]

\c FCMOVE fpureg                 ; DA C8+r              [P6,FPU]
\c FCMOVE ST0,fpureg             ; DA C8+r              [P6,FPU]

\c FCMOVBE fpureg                ; DA D0+r              [P6,FPU]
\c FCMOVBE ST0,fpureg            ; DA D0+r              [P6,FPU]

\c FCMOVU fpureg                 ; DA D8+r              [P6,FPU]
\c FCMOVU ST0,fpureg             ; DA D8+r              [P6,FPU]

\c FCMOVNB fpureg                ; DB C0+r              [P6,FPU]
\c FCMOVNB ST0,fpureg            ; DB C0+r              [P6,FPU]

\c FCMOVNE fpureg                ; DB C8+r              [P6,FPU]
\c FCMOVNE ST0,fpureg            ; DB C8+r              [P6,FPU]

\c FCMOVNBE fpureg               ; DB D0+r              [P6,FPU]
\c FCMOVNBE ST0,fpureg           ; DB D0+r              [P6,FPU]

\c FCMOVNU fpureg                ; DB D8+r              [P6,FPU]
\c FCMOVNU ST0,fpureg            ; DB D8+r              [P6,FPU]

The \c{FCMOV} instructions perform conditional move operations: each
of them moves the contents of the given register into \c{ST0} if its
condition is satisfied, and does nothing if not.

The conditions are not the same as the standard condition codes used
with conditional jump instructions. The conditions \c{B}, \c{BE},
\c{NB}, \c{NBE}, \c{E} and \c{NE} are exactly as normal, but none of
the other standard ones are supported. Instead, the condition \c{U}
and its counterpart \c{NU} are provided; the \c{U} condition is
satisfied if the last two floating-point numbers compared were
\e{unordered}, i.e. they were not equal but neither one could be
said to be greater than the other, for example if they were NaNs.
(The flag state which signals this is the setting of the parity
flag: so the \c{U} condition is notionally equivalent to \c{PE}, and
\c{NU} is equivalent to \c{PO}.)

The \c{FCMOV} conditions test the main processor's status flags, not
the FPU status flags, so using \c{FCMOV} directly after \c{FCOM}
will not work. Instead, you should either use \c{FCOMI} which writes
directly to the main CPU flags word, or use \c{FSTSW} to extract the
FPU flags.

Although the \c{FCMOV} instructions are flagged \c{P6} above, they
may not be supported by all Pentium Pro processors; the \c{CPUID}
instruction (\k{insCPUID}) will return a bit which indicates whether
conditional moves are supported.


\S{insFCOM} \i\c{FCOM}, \i\c{FCOMP}, \i\c{FCOMPP}, \i\c{FCOMI},
\i\c{FCOMIP}: Floating-Point Compare

\c FCOM mem32                    ; D8 /2                [8086,FPU]
\c FCOM mem64                    ; DC /2                [8086,FPU]
\c FCOM fpureg                   ; D8 D0+r              [8086,FPU]
\c FCOM ST0,fpureg               ; D8 D0+r              [8086,FPU]

\c FCOMP mem32                   ; D8 /3                [8086,FPU]
\c FCOMP mem64                   ; DC /3                [8086,FPU]
\c FCOMP fpureg                  ; D8 D8+r              [8086,FPU]
\c FCOMP ST0,fpureg              ; D8 D8+r              [8086,FPU]

\c FCOMPP                        ; DE D9                [8086,FPU]

\c FCOMI fpureg                  ; DB F0+r              [P6,FPU]
\c FCOMI ST0,fpureg              ; DB F0+r              [P6,FPU]

\c FCOMIP fpureg                 ; DF F0+r              [P6,FPU]
\c FCOMIP ST0,fpureg             ; DF F0+r              [P6,FPU]

\c{FCOM} compares \c{ST0} with the given operand, and sets the FPU
flags accordingly. \c{ST0} is treated as the left-hand side of the
comparison, so that the carry flag is set (for a `less-than' result)
if \c{ST0} is less than the given operand.

\c{FCOMP} does the same as \c{FCOM}, but pops the register stack
afterwards. \c{FCOMPP} compares \c{ST0} with \c{ST1} and then pops
the register stack twice.

\c{FCOMI} and \c{FCOMIP} work like the corresponding forms of
\c{FCOM} and \c{FCOMP}, but write their results directly to the CPU
flags register rather than the FPU status word, so they can be
immediately followed by conditional jump or conditional move
instructions.

The \c{FCOM} instructions differ from the \c{FUCOM} instructions
(\k{insFUCOM}) only in the way they handle quiet NaNs: \c{FUCOM}
will handle them silently and set the condition code flags to an
`unordered' result, whereas \c{FCOM} will generate an exception.


\S{insFCOS} \i\c{FCOS}: Cosine

\c FCOS                          ; D9 FF                [386,FPU]

\c{FCOS} computes the cosine of \c{ST0} (in radians), and stores the
result in \c{ST0}. The absolute value of \c{ST0} must be less than 2**63.

See also \c{FSINCOS} (\k{insFSIN}).


\S{insFDECSTP} \i\c{FDECSTP}: Decrement Floating-Point Stack Pointer

\c FDECSTP                       ; D9 F6                [8086,FPU]

\c{FDECSTP} decrements the `top' field in the floating-point status
word. This has the effect of rotating the FPU register stack by one,
as if the contents of \c{ST7} had been pushed on the stack. See also
\c{FINCSTP} (\k{insFINCSTP}).


\S{insFDISI} \i\c{FxDISI}, \i\c{FxENI}: Disable and Enable Floating-Point Interrupts

\c FDISI                         ; 9B DB E1             [8086,FPU]
\c FNDISI                        ; DB E1                [8086,FPU]

\c FENI                          ; 9B DB E0             [8086,FPU]
\c FNENI                         ; DB E0                [8086,FPU]

\c{FDISI} and \c{FENI} disable and enable floating-point interrupts.
These instructions are only meaningful on original 8087 processors:
the 287 and above treat them as no-operation instructions.

\c{FNDISI} and \c{FNENI} do the same thing as \c{FDISI} and \c{FENI}
respectively, but without waiting for the floating-point processor
to finish what it was doing first.


\S{insFDIV} \i\c{FDIV}, \i\c{FDIVP}, \i\c{FDIVR}, \i\c{FDIVRP}: Floating-Point Division

\c FDIV mem32                    ; D8 /6                [8086,FPU]
\c FDIV mem64                    ; DC /6                [8086,FPU]

\c FDIV fpureg                   ; D8 F0+r              [8086,FPU]
\c FDIV ST0,fpureg               ; D8 F0+r              [8086,FPU]

\c FDIV TO fpureg                ; DC F8+r              [8086,FPU]
\c FDIV fpureg,ST0               ; DC F8+r              [8086,FPU]

\c FDIVR mem32                   ; D8 /7                [8086,FPU]
\c FDIVR mem64                   ; DC /7                [8086,FPU]

\c FDIVR fpureg                  ; D8 F8+r              [8086,FPU]
\c FDIVR ST0,fpureg              ; D8 F8+r              [8086,FPU]

\c FDIVR TO fpureg               ; DC F0+r              [8086,FPU]
\c FDIVR fpureg,ST0              ; DC F0+r              [8086,FPU]

\c FDIVP fpureg                  ; DE F8+r              [8086,FPU]
\c FDIVP fpureg,ST0              ; DE F8+r              [8086,FPU]

\c FDIVRP fpureg                 ; DE F0+r              [8086,FPU]
\c FDIVRP fpureg,ST0             ; DE F0+r              [8086,FPU]

\b \c{FDIV} divides \c{ST0} by the given operand and stores the result
back in \c{ST0}, unless the \c{TO} qualifier is given, in which case
it divides the given operand by \c{ST0} and stores the result in the
operand.

\b \c{FDIVR} does the same thing, but does the division the other way
up: so if \c{TO} is not given, it divides the given operand by
\c{ST0} and stores the result in \c{ST0}, whereas if \c{TO} is given
it divides \c{ST0} by its operand and stores the result in the
operand.

\b \c{FDIVP} operates like \c{FDIV TO}, but pops the register stack
once it has finished.

\b \c{FDIVRP} operates like \c{FDIVR TO}, but pops the register stack
once it has finished.

For FP/Integer divisions, see \c{FIDIV} (\k{insFIDIV}).


\S{insFEMMS} \i\c{FEMMS}: Faster Enter/Exit of the MMX or floating-point state

\c FEMMS                         ; 0F 0E           [PENT,3DNOW]

\c{FEMMS} can be used in place of the \c{EMMS} instruction on
processors which support the 3DNow! instruction set. Following
execution of \c{FEMMS}, the state of the \c{MMX/FP} registers
is undefined, and this allows a faster context switch between
\c{FP} and \c{MMX} instructions. The \c{FEMMS} instruction can
also be used \e{before} executing \c{MMX} instructions


\S{insFFREE} \i\c{FFREE}: Flag Floating-Point Register as Unused

\c FFREE fpureg                  ; DD C0+r              [8086,FPU]
\c FFREEP fpureg                 ; DF C0+r              [286,FPU,UNDOC]

\c{FFREE} marks the given register as being empty.

\c{FFREEP} marks the given register as being empty, and then
pops the register stack.


\S{insFIADD} \i\c{FIADD}: Floating-Point/Integer Addition

\c FIADD mem16                   ; DE /0                [8086,FPU]
\c FIADD mem32                   ; DA /0                [8086,FPU]

\c{FIADD} adds the 16-bit or 32-bit integer stored in the given
memory location to \c{ST0}, storing the result in \c{ST0}.


\S{insFICOM} \i\c{FICOM}, \i\c{FICOMP}: Floating-Point/Integer Compare

\c FICOM mem16                   ; DE /2                [8086,FPU]
\c FICOM mem32                   ; DA /2                [8086,FPU]

\c FICOMP mem16                  ; DE /3                [8086,FPU]
\c FICOMP mem32                  ; DA /3                [8086,FPU]

\c{FICOM} compares \c{ST0} with the 16-bit or 32-bit integer stored
in the given memory location, and sets the FPU flags accordingly.
\c{FICOMP} does the same, but pops the register stack afterwards.


\S{insFIDIV} \i\c{FIDIV}, \i\c{FIDIVR}: Floating-Point/Integer Division

\c FIDIV mem16                   ; DE /6                [8086,FPU]
\c FIDIV mem32                   ; DA /6                [8086,FPU]

\c FIDIVR mem16                  ; DE /7                [8086,FPU]
\c FIDIVR mem32                  ; DA /7                [8086,FPU]

\c{FIDIV} divides \c{ST0} by the 16-bit or 32-bit integer stored in
the given memory location, and stores the result in \c{ST0}.
\c{FIDIVR} does the division the other way up: it divides the
integer by \c{ST0}, but still stores the result in \c{ST0}.


\S{insFILD} \i\c{FILD}, \i\c{FIST}, \i\c{FISTP}: Floating-Point/Integer Conversion

\c FILD mem16                    ; DF /0                [8086,FPU]
\c FILD mem32                    ; DB /0                [8086,FPU]
\c FILD mem64                    ; DF /5                [8086,FPU]

\c FIST mem16                    ; DF /2                [8086,FPU]
\c FIST mem32                    ; DB /2                [8086,FPU]

\c FISTP mem16                   ; DF /3                [8086,FPU]
\c FISTP mem32                   ; DB /3                [8086,FPU]
\c FISTP mem64                   ; DF /7                [8086,FPU]

\c{FILD} loads an integer out of a memory location, converts it to a
real, and pushes it on the FPU register stack. \c{FIST} converts
\c{ST0} to an integer and stores that in memory; \c{FISTP} does the
same as \c{FIST}, but pops the register stack afterwards.


\S{insFIMUL} \i\c{FIMUL}: Floating-Point/Integer Multiplication

\c FIMUL mem16                   ; DE /1                [8086,FPU]
\c FIMUL mem32                   ; DA /1                [8086,FPU]

\c{FIMUL} multiplies \c{ST0} by the 16-bit or 32-bit integer stored
in the given memory location, and stores the result in \c{ST0}.


\S{insFINCSTP} \i\c{FINCSTP}: Increment Floating-Point Stack Pointer

\c FINCSTP                       ; D9 F7                [8086,FPU]

\c{FINCSTP} increments the `top' field in the floating-point status
word. This has the effect of rotating the FPU register stack by one,
as if the register stack had been popped; however, unlike the
popping of the stack performed by many FPU instructions, it does not
flag the new \c{ST7} (previously \c{ST0}) as empty. See also
\c{FDECSTP} (\k{insFDECSTP}).


\S{insFINIT} \i\c{FINIT}, \i\c{FNINIT}: initialize Floating-Point Unit

\c FINIT                         ; 9B DB E3             [8086,FPU]
\c FNINIT                        ; DB E3                [8086,FPU]

\c{FINIT} initializes the FPU to its default state. It flags all
registers as empty, without actually change their values, clears
the top of stack pointer. \c{FNINIT} does the same, without first
waiting for pending exceptions to clear.


\S{insFISUB} \i\c{FISUB}: Floating-Point/Integer Subtraction

\c FISUB mem16                   ; DE /4                [8086,FPU]
\c FISUB mem32                   ; DA /4                [8086,FPU]

\c FISUBR mem16                  ; DE /5                [8086,FPU]
\c FISUBR mem32                  ; DA /5                [8086,FPU]

\c{FISUB} subtracts the 16-bit or 32-bit integer stored in the given
memory location from \c{ST0}, and stores the result in \c{ST0}.
\c{FISUBR} does the subtraction the other way round, i.e. it
subtracts \c{ST0} from the given integer, but still stores the
result in \c{ST0}.


\S{insFLD} \i\c{FLD}: Floating-Point Load

\c FLD mem32                     ; D9 /0                [8086,FPU]
\c FLD mem64                     ; DD /0                [8086,FPU]
\c FLD mem80                     ; DB /5                [8086,FPU]
\c FLD fpureg                    ; D9 C0+r              [8086,FPU]

\c{FLD} loads a floating-point value out of the given register or
memory location, and pushes it on the FPU register stack.


\S{insFLD1} \i\c{FLDxx}: Floating-Point Load Constants

\c FLD1                          ; D9 E8                [8086,FPU]
\c FLDL2E                        ; D9 EA                [8086,FPU]
\c FLDL2T                        ; D9 E9                [8086,FPU]
\c FLDLG2                        ; D9 EC                [8086,FPU]
\c FLDLN2                        ; D9 ED                [8086,FPU]
\c FLDPI                         ; D9 EB                [8086,FPU]
\c FLDZ                          ; D9 EE                [8086,FPU]

These instructions push specific standard constants on the FPU
register stack.

\c  Instruction    Constant pushed

\c  FLD1           1
\c  FLDL2E         base-2 logarithm of e
\c  FLDL2T         base-2 log of 10
\c  FLDLG2         base-10 log of 2
\c  FLDLN2         base-e log of 2
\c  FLDPI          pi
\c  FLDZ           zero


\S{insFLDCW} \i\c{FLDCW}: Load Floating-Point Control Word

\c FLDCW mem16                   ; D9 /5                [8086,FPU]

\c{FLDCW} loads a 16-bit value out of memory and stores it into the
FPU control word (governing things like the rounding mode, the
precision, and the exception masks). See also \c{FSTCW}
(\k{insFSTCW}). If exceptions are enabled and you don't want to
generate one, use \c{FCLEX} or \c{FNCLEX} (\k{insFCLEX}) before
loading the new control word.


\S{insFLDENV} \i\c{FLDENV}: Load Floating-Point Environment

\c FLDENV mem                    ; D9 /4                [8086,FPU]

\c{FLDENV} loads the FPU operating environment (control word, status
word, tag word, instruction pointer, data pointer and last opcode)
from memory. The memory area is 14 or 28 bytes long, depending on
the CPU mode at the time. See also \c{FSTENV} (\k{insFSTENV}).


\S{insFMUL} \i\c{FMUL}, \i\c{FMULP}: Floating-Point Multiply

\c FMUL mem32                    ; D8 /1                [8086,FPU]
\c FMUL mem64                    ; DC /1                [8086,FPU]

\c FMUL fpureg                   ; D8 C8+r              [8086,FPU]
\c FMUL ST0,fpureg               ; D8 C8+r              [8086,FPU]

\c FMUL TO fpureg                ; DC C8+r              [8086,FPU]
\c FMUL fpureg,ST0               ; DC C8+r              [8086,FPU]

\c FMULP fpureg                  ; DE C8+r              [8086,FPU]
\c FMULP fpureg,ST0              ; DE C8+r              [8086,FPU]

\c{FMUL} multiplies \c{ST0} by the given operand, and stores the
result in \c{ST0}, unless the \c{TO} qualifier is used in which case
it stores the result in the operand. \c{FMULP} performs the same
operation as \c{FMUL TO}, and then pops the register stack.


\S{insFNOP} \i\c{FNOP}: Floating-Point No Operation

\c FNOP                          ; D9 D0                [8086,FPU]

\c{FNOP} does nothing.


\S{insFPATAN} \i\c{FPATAN}, \i\c{FPTAN}: Arctangent and Tangent

\c FPATAN                        ; D9 F3                [8086,FPU]
\c FPTAN                         ; D9 F2                [8086,FPU]

\c{FPATAN} computes the arctangent, in radians, of the result of
dividing \c{ST1} by \c{ST0}, stores the result in \c{ST1}, and pops
the register stack. It works like the C \c{atan2} function, in that
changing the sign of both \c{ST0} and \c{ST1} changes the output
value by pi (so it performs true rectangular-to-polar coordinate
conversion, with \c{ST1} being the Y coordinate and \c{ST0} being
the X coordinate, not merely an arctangent).

\c{FPTAN} computes the tangent of the value in \c{ST0} (in radians),
and stores the result back into \c{ST0}.

The absolute value of \c{ST0} must be less than 2**63.


\S{insFPREM} \i\c{FPREM}, \i\c{FPREM1}: Floating-Point Partial Remainder

\c FPREM                         ; D9 F8                [8086,FPU]
\c FPREM1                        ; D9 F5                [386,FPU]

These instructions both produce the remainder obtained by dividing
\c{ST0} by \c{ST1}. This is calculated, notionally, by dividing
\c{ST0} by \c{ST1}, rounding the result to an integer, multiplying
by \c{ST1} again, and computing the value which would need to be
added back on to the result to get back to the original value in
\c{ST0}.

The two instructions differ in the way the notional round-to-integer
operation is performed. \c{FPREM} does it by rounding towards zero,
so that the remainder it returns always has the same sign as the
original value in \c{ST0}; \c{FPREM1} does it by rounding to the
nearest integer, so that the remainder always has at most half the
magnitude of \c{ST1}.

Both instructions calculate \e{partial} remainders, meaning that
they may not manage to provide the final result, but might leave
intermediate results in \c{ST0} instead. If this happens, they will
set the C2 flag in the FPU status word; therefore, to calculate a
remainder, you should repeatedly execute \c{FPREM} or \c{FPREM1}
until C2 becomes clear.


\S{insFRNDINT} \i\c{FRNDINT}: Floating-Point Round to Integer

\c FRNDINT                       ; D9 FC                [8086,FPU]

\c{FRNDINT} rounds the contents of \c{ST0} to an integer, according
to the current rounding mode set in the FPU control word, and stores
the result back in \c{ST0}.


\S{insFRSTOR} \i\c{FSAVE}, \i\c{FRSTOR}: Save/Restore Floating-Point State

\c FSAVE mem                     ; 9B DD /6             [8086,FPU]
\c FNSAVE mem                    ; DD /6                [8086,FPU]

\c FRSTOR mem                    ; DD /4                [8086,FPU]

\c{FSAVE} saves the entire floating-point unit state, including all
the information saved by \c{FSTENV} (\k{insFSTENV}) plus the
contents of all the registers, to a 94 or 108 byte area of memory
(depending on the CPU mode). \c{FRSTOR} restores the floating-point
state from the same area of memory.

\c{FNSAVE} does the same as \c{FSAVE}, without first waiting for
pending floating-point exceptions to clear.


\S{insFSCALE} \i\c{FSCALE}: Scale Floating-Point Value by Power of Two

\c FSCALE                        ; D9 FD                [8086,FPU]

\c{FSCALE} scales a number by a power of two: it rounds \c{ST1}
towards zero to obtain an integer, then multiplies \c{ST0} by two to
the power of that integer, and stores the result in \c{ST0}.


\S{insFSETPM} \i\c{FSETPM}: Set Protected Mode

\c FSETPM                        ; DB E4                [286,FPU]

This instruction initializes protected mode on the 287 floating-point
coprocessor. It is only meaningful on that processor: the 387 and
above treat the instruction as a no-operation.


\S{insFSIN} \i\c{FSIN}, \i\c{FSINCOS}: Sine and Cosine

\c FSIN                          ; D9 FE                [386,FPU]
\c FSINCOS                       ; D9 FB                [386,FPU]

\c{FSIN} calculates the sine of \c{ST0} (in radians) and stores the
result in \c{ST0}. \c{FSINCOS} does the same, but then pushes the
cosine of the same value on the register stack, so that the sine
ends up in \c{ST1} and the cosine in \c{ST0}. \c{FSINCOS} is faster
than executing \c{FSIN} and \c{FCOS} (see \k{insFCOS}) in succession.

The absolute value of \c{ST0} must be less than 2**63.


\S{insFSQRT} \i\c{FSQRT}: Floating-Point Square Root

\c FSQRT                         ; D9 FA                [8086,FPU]

\c{FSQRT} calculates the square root of \c{ST0} and stores the
result in \c{ST0}.


\S{insFST} \i\c{FST}, \i\c{FSTP}: Floating-Point Store

\c FST mem32                     ; D9 /2                [8086,FPU]
\c FST mem64                     ; DD /2                [8086,FPU]
\c FST fpureg                    ; DD D0+r              [8086,FPU]

\c FSTP mem32                    ; D9 /3                [8086,FPU]
\c FSTP mem64                    ; DD /3                [8086,FPU]
\c FSTP mem80                    ; DB /7                [8086,FPU]
\c FSTP fpureg                   ; DD D8+r              [8086,FPU]

\c{FST} stores the value in \c{ST0} into the given memory location
or other FPU register. \c{FSTP} does the same, but then pops the
register stack.


\S{insFSTCW} \i\c{FSTCW}: Store Floating-Point Control Word

\c FSTCW mem16                   ; 9B D9 /7             [8086,FPU]
\c FNSTCW mem16                  ; D9 /7                [8086,FPU]

\c{FSTCW} stores the \c{FPU} control word (governing things like the
rounding mode, the precision, and the exception masks) into a 2-byte
memory area. See also \c{FLDCW} (\k{insFLDCW}).

\c{FNSTCW} does the same thing as \c{FSTCW}, without first waiting
for pending floating-point exceptions to clear.


\S{insFSTENV} \i\c{FSTENV}: Store Floating-Point Environment

\c FSTENV mem                    ; 9B D9 /6             [8086,FPU]
\c FNSTENV mem                   ; D9 /6                [8086,FPU]

\c{FSTENV} stores the \c{FPU} operating environment (control word,
status word, tag word, instruction pointer, data pointer and last
opcode) into memory. The memory area is 14 or 28 bytes long,
depending on the CPU mode at the time. See also \c{FLDENV}
(\k{insFLDENV}).

\c{FNSTENV} does the same thing as \c{FSTENV}, without first waiting
for pending floating-point exceptions to clear.


\S{insFSTSW} \i\c{FSTSW}: Store Floating-Point Status Word

\c FSTSW mem16                   ; 9B DD /7             [8086,FPU]
\c FSTSW AX                      ; 9B DF E0             [286,FPU]

\c FNSTSW mem16                  ; DD /7                [8086,FPU]
\c FNSTSW AX                     ; DF E0                [286,FPU]

\c{FSTSW} stores the \c{FPU} status word into \c{AX} or into a 2-byte
memory area.

\c{FNSTSW} does the same thing as \c{FSTSW}, without first waiting
for pending floating-point exceptions to clear.


\S{insFSUB} \i\c{FSUB}, \i\c{FSUBP}, \i\c{FSUBR}, \i\c{FSUBRP}: Floating-Point Subtract

\c FSUB mem32                    ; D8 /4                [8086,FPU]
\c FSUB mem64                    ; DC /4                [8086,FPU]

\c FSUB fpureg                   ; D8 E0+r              [8086,FPU]
\c FSUB ST0,fpureg               ; D8 E0+r              [8086,FPU]

\c FSUB TO fpureg                ; DC E8+r              [8086,FPU]
\c FSUB fpureg,ST0               ; DC E8+r              [8086,FPU]

\c FSUBR mem32                   ; D8 /5                [8086,FPU]
\c FSUBR mem64                   ; DC /5                [8086,FPU]

\c FSUBR fpureg                  ; D8 E8+r              [8086,FPU]
\c FSUBR ST0,fpureg              ; D8 E8+r              [8086,FPU]

\c FSUBR TO fpureg               ; DC E0+r              [8086,FPU]
\c FSUBR fpureg,ST0              ; DC E0+r              [8086,FPU]

\c FSUBP fpureg                  ; DE E8+r              [8086,FPU]
\c FSUBP fpureg,ST0              ; DE E8+r              [8086,FPU]

\c FSUBRP fpureg                 ; DE E0+r              [8086,FPU]
\c FSUBRP fpureg,ST0             ; DE E0+r              [8086,FPU]

\b \c{FSUB} subtracts the given operand from \c{ST0} and stores the
result back in \c{ST0}, unless the \c{TO} qualifier is given, in
which case it subtracts \c{ST0} from the given operand and stores
the result in the operand.

\b \c{FSUBR} does the same thing, but does the subtraction the other
way up: so if \c{TO} is not given, it subtracts \c{ST0} from the given
operand and stores the result in \c{ST0}, whereas if \c{TO} is given
it subtracts its operand from \c{ST0} and stores the result in the
operand.

\b \c{FSUBP} operates like \c{FSUB TO}, but pops the register stack
once it has finished.

\b \c{FSUBRP} operates like \c{FSUBR TO}, but pops the register stack
once it has finished.


\S{insFTST} \i\c{FTST}: Test \c{ST0} Against Zero

\c FTST                          ; D9 E4                [8086,FPU]

\c{FTST} compares \c{ST0} with zero and sets the FPU flags
accordingly. \c{ST0} is treated as the left-hand side of the
comparison, so that a `less-than' result is generated if \c{ST0} is
negative.


\S{insFUCOM} \i\c{FUCOMxx}: Floating-Point Unordered Compare

\c FUCOM fpureg                  ; DD E0+r              [386,FPU]
\c FUCOM ST0,fpureg              ; DD E0+r              [386,FPU]

\c FUCOMP fpureg                 ; DD E8+r              [386,FPU]
\c FUCOMP ST0,fpureg             ; DD E8+r              [386,FPU]

\c FUCOMPP                       ; DA E9                [386,FPU]

\c FUCOMI fpureg                 ; DB E8+r              [P6,FPU]
\c FUCOMI ST0,fpureg             ; DB E8+r              [P6,FPU]

\c FUCOMIP fpureg                ; DF E8+r              [P6,FPU]
\c FUCOMIP ST0,fpureg            ; DF E8+r              [P6,FPU]

\b \c{FUCOM} compares \c{ST0} with the given operand, and sets the
FPU flags accordingly. \c{ST0} is treated as the left-hand side of
the comparison, so that the carry flag is set (for a `less-than'
result) if \c{ST0} is less than the given operand.

\b \c{FUCOMP} does the same as \c{FUCOM}, but pops the register stack
afterwards. \c{FUCOMPP} compares \c{ST0} with \c{ST1} and then pops
the register stack twice.

\b \c{FUCOMI} and \c{FUCOMIP} work like the corresponding forms of
\c{FUCOM} and \c{FUCOMP}, but write their results directly to the CPU
flags register rather than the FPU status word, so they can be
immediately followed by conditional jump or conditional move
instructions.

The \c{FUCOM} instructions differ from the \c{FCOM} instructions
(\k{insFCOM}) only in the way they handle quiet NaNs: \c{FUCOM} will
handle them silently and set the condition code flags to an
`unordered' result, whereas \c{FCOM} will generate an exception.


\S{insFXAM} \i\c{FXAM}: Examine Class of Value in \c{ST0}

\c FXAM                          ; D9 E5                [8086,FPU]

\c{FXAM} sets the FPU flags \c{C3}, \c{C2} and \c{C0} depending on
the type of value stored in \c{ST0}:

\c  Register contents     Flags

\c  Unsupported format    000
\c  NaN                   001
\c  Finite number         010
\c  Infinity              011
\c  Zero                  100
\c  Empty register        101
\c  Denormal              110

Additionally, the \c{C1} flag is set to the sign of the number.


\S{insFXCH} \i\c{FXCH}: Floating-Point Exchange

\c FXCH                          ; D9 C9                [8086,FPU]
\c FXCH fpureg                   ; D9 C8+r              [8086,FPU]
\c FXCH fpureg,ST0               ; D9 C8+r              [8086,FPU]
\c FXCH ST0,fpureg               ; D9 C8+r              [8086,FPU]

\c{FXCH} exchanges \c{ST0} with a given FPU register. The no-operand
form exchanges \c{ST0} with \c{ST1}.


\S{insFXRSTOR} \i\c{FXRSTOR}: Restore \c{FP}, \c{MMX} and \c{SSE} State

\c FXRSTOR memory                ; 0F AE /1               [P6,SSE,FPU]

The \c{FXRSTOR} instruction reloads the \c{FPU}, \c{MMX} and \c{SSE}
state (environment and registers), from the 512 byte memory area defined
by the source operand. This data should have been written by a previous
\c{FXSAVE}.


\S{insFXSAVE} \i\c{FXSAVE}: Store \c{FP}, \c{MMX} and \c{SSE} State

\c FXSAVE memory                 ; 0F AE /0         [P6,SSE,FPU]

\c{FXSAVE}The FXSAVE instruction writes the current \c{FPU}, \c{MMX}
and \c{SSE} technology states (environment and registers), to the
512 byte memory area defined by the destination operand. It does this
without checking for pending unmasked floating-point exceptions
(similar to the operation of \c{FNSAVE}).

Unlike the \c{FSAVE/FNSAVE} instructions, the processor retains the
contents of the \c{FPU}, \c{MMX} and \c{SSE} state in the processor
after the state has been saved. This instruction has been optimized
to maximize floating-point save performance.


\S{insFXTRACT} \i\c{FXTRACT}: Extract Exponent and Significand

\c FXTRACT                       ; D9 F4                [8086,FPU]

\c{FXTRACT} separates the number in \c{ST0} into its exponent and
significand (mantissa), stores the exponent back into \c{ST0}, and
then pushes the significand on the register stack (so that the
significand ends up in \c{ST0}, and the exponent in \c{ST1}).


\S{insFYL2X} \i\c{FYL2X}, \i\c{FYL2XP1}: Compute Y times Log2(X) or Log2(X+1)

\c FYL2X                         ; D9 F1                [8086,FPU]
\c FYL2XP1                       ; D9 F9                [8086,FPU]

\c{FYL2X} multiplies \c{ST1} by the base-2 logarithm of \c{ST0},
stores the result in \c{ST1}, and pops the register stack (so that
the result ends up in \c{ST0}). \c{ST0} must be non-zero and
positive.

\c{FYL2XP1} works the same way, but replacing the base-2 log of
\c{ST0} with that of \c{ST0} plus one. This time, \c{ST0} must have
magnitude no greater than 1 minus half the square root of two.


\S{insHLT} \i\c{HLT}: Halt Processor

\c HLT                           ; F4                   [8086,PRIV]

\c{HLT} puts the processor into a halted state, where it will
perform no more operations until restarted by an interrupt or a
reset.

On the 286 and later processors, this is a privileged instruction.


\S{insIBTS} \i\c{IBTS}: Insert Bit String

\c IBTS r/m16,reg16              ; o16 0F A7 /r         [386,UNDOC]
\c IBTS r/m32,reg32              ; o32 0F A7 /r         [386,UNDOC]

The implied operation of this instruction is:

\c IBTS r/m16,AX,CL,reg16
\c IBTS r/m32,EAX,CL,reg32

Writes a bit string from the source operand to the destination.
\c{CL} indicates the number of bits to be copied, from the low bits
of the source. \c{(E)AX} indicates the low order bit offset in the
destination that is written to. For example, if \c{CL} is set to 4
and \c{AX} (for 16-bit code) is set to 5, bits 0-3 of \c{src} will
be copied to bits 5-8 of \c{dst}. This instruction is very poorly
documented, and I have been unable to find any official source of
documentation on it.

\c{IBTS} is supported only on the early Intel 386s, and conflicts
with the opcodes for \c{CMPXCHG486} (on early Intel 486s). NASM
supports it only for completeness. Its counterpart is \c{XBTS}
(see \k{insXBTS}).


\S{insIDIV} \i\c{IDIV}: Signed Integer Divide

\c IDIV r/m8                     ; F6 /7                [8086]
\c IDIV r/m16                    ; o16 F7 /7            [8086]
\c IDIV r/m32                    ; o32 F7 /7            [386]

\c{IDIV} performs signed integer division. The explicit operand
provided is the divisor; the dividend and destination operands
are implicit, in the following way:

\b For \c{IDIV r/m8}, \c{AX} is divided by the given operand;
the quotient is stored in \c{AL} and the remainder in \c{AH}.

\b For \c{IDIV r/m16}, \c{DX:AX} is divided by the given operand;
the quotient is stored in \c{AX} and the remainder in \c{DX}.

\b For \c{IDIV r/m32}, \c{EDX:EAX} is divided by the given operand;
the quotient is stored in \c{EAX} and the remainder in \c{EDX}.

Unsigned integer division is performed by the \c{DIV} instruction:
see \k{insDIV}.


\S{insIMUL} \i\c{IMUL}: Signed Integer Multiply

\c IMUL r/m8                     ; F6 /5                [8086]
\c IMUL r/m16                    ; o16 F7 /5            [8086]
\c IMUL r/m32                    ; o32 F7 /5            [386]

\c IMUL reg16,r/m16              ; o16 0F AF /r         [386]
\c IMUL reg32,r/m32              ; o32 0F AF /r         [386]

\c IMUL reg16,imm8               ; o16 6B /r ib         [186]
\c IMUL reg16,imm16              ; o16 69 /r iw         [186]
\c IMUL reg32,imm8               ; o32 6B /r ib         [386]
\c IMUL reg32,imm32              ; o32 69 /r id         [386]

\c IMUL reg16,r/m16,imm8         ; o16 6B /r ib         [186]
\c IMUL reg16,r/m16,imm16        ; o16 69 /r iw         [186]
\c IMUL reg32,r/m32,imm8         ; o32 6B /r ib         [386]
\c IMUL reg32,r/m32,imm32        ; o32 69 /r id         [386]

\c{IMUL} performs signed integer multiplication. For the
single-operand form, the other operand and destination are
implicit, in the following way:

\b For \c{IMUL r/m8}, \c{AL} is multiplied by the given operand;
the product is stored in \c{AX}.

\b For \c{IMUL r/m16}, \c{AX} is multiplied by the given operand;
the product is stored in \c{DX:AX}.

\b For \c{IMUL r/m32}, \c{EAX} is multiplied by the given operand;
the product is stored in \c{EDX:EAX}.

The two-operand form multiplies its two operands and stores the
result in the destination (first) operand. The three-operand
form multiplies its last two operands and stores the result in
the first operand.

The two-operand form with an immediate second operand is in
fact a shorthand for the three-operand form, as can be seen by
examining the opcode descriptions: in the two-operand form, the
code \c{/r} takes both its register and \c{r/m} parts from the
same operand (the first one).

In the forms with an 8-bit immediate operand and another longer
source operand, the immediate operand is considered to be signed,
and is sign-extended to the length of the other source operand.
In these cases, the \c{BYTE} qualifier is necessary to force
NASM to generate this form of the instruction.

Unsigned integer multiplication is performed by the \c{MUL}
instruction: see \k{insMUL}.


\S{insIN} \i\c{IN}: Input from I/O Port

\c IN AL,imm8                    ; E4 ib                [8086]
\c IN AX,imm8                    ; o16 E5 ib            [8086]
\c IN EAX,imm8                   ; o32 E5 ib            [386]
\c IN AL,DX                      ; EC                   [8086]
\c IN AX,DX                      ; o16 ED               [8086]
\c IN EAX,DX                     ; o32 ED               [386]

\c{IN} reads a byte, word or doubleword from the specified I/O port,
and stores it in the given destination register. The port number may
be specified as an immediate value if it is between 0 and 255, and
otherwise must be stored in \c{DX}. See also \c{OUT} (\k{insOUT}).


\S{insINC} \i\c{INC}: Increment Integer

\c INC reg16                     ; o16 40+r             [8086]
\c INC reg32                     ; o32 40+r             [386]
\c INC r/m8                      ; FE /0                [8086]
\c INC r/m16                     ; o16 FF /0            [8086]
\c INC r/m32                     ; o32 FF /0            [386]

\c{INC} adds 1 to its operand. It does \e{not} affect the carry
flag: to affect the carry flag, use \c{ADD something,1} (see
\k{insADD}). \c{INC} affects all the other flags according to the result.

This instruction can be used with a \c{LOCK} prefix to allow atomic execution.

See also \c{DEC} (\k{insDEC}).


\S{insINSB} \i\c{INSB}, \i\c{INSW}, \i\c{INSD}: Input String from I/O Port

\c INSB                          ; 6C                   [186]
\c INSW                          ; o16 6D               [186]
\c INSD                          ; o32 6D               [386]

\c{INSB} inputs a byte from the I/O port specified in \c{DX} and
stores it at \c{[ES:DI]} or \c{[ES:EDI]}. It then increments or
decrements (depending on the direction flag: increments if the flag
is clear, decrements if it is set) \c{DI} or \c{EDI}.

The register used is \c{DI} if the address size is 16 bits, and
\c{EDI} if it is 32 bits. If you need to use an address size not
equal to the current \c{BITS} setting, you can use an explicit
\i\c{a16} or \i\c{a32} prefix.

Segment override prefixes have no effect for this instruction: the
use of \c{ES} for the load from \c{[DI]} or \c{[EDI]} cannot be
overridden.

\c{INSW} and \c{INSD} work in the same way, but they input a word or
a doubleword instead of a byte, and increment or decrement the
addressing register by 2 or 4 instead of 1.

The \c{REP} prefix may be used to repeat the instruction \c{CX} (or
\c{ECX} - again, the address size chooses which) times.

See also \c{OUTSB}, \c{OUTSW} and \c{OUTSD} (\k{insOUTSB}).


\S{insINT} \i\c{INT}: Software Interrupt

\c INT imm8                      ; CD ib                [8086]

\c{INT} causes a software interrupt through a specified vector
number from 0 to 255.

The code generated by the \c{INT} instruction is always two bytes
long: although there are short forms for some \c{INT} instructions,
NASM does not generate them when it sees the \c{INT} mnemonic. In
order to generate single-byte breakpoint instructions, use the
\c{INT3} or \c{INT1} instructions (see \k{insINT1}) instead.


\S{insINT1} \i\c{INT3}, \i\c{INT1}, \i\c{ICEBP}, \i\c{INT01}: Breakpoints

\c INT1                          ; F1                   [P6]
\c ICEBP                         ; F1                   [P6]
\c INT01                         ; F1                   [P6]

\c INT3                          ; CC                   [8086]
\c INT03                         ; CC                   [8086]

\c{INT1} and \c{INT3} are short one-byte forms of the instructions
\c{INT 1} and \c{INT 3} (see \k{insINT}). They perform a similar
function to their longer counterparts, but take up less code space.
They are used as breakpoints by debuggers.

\b \c{INT1}, and its alternative synonyms \c{INT01} and \c{ICEBP}, is
an instruction used by in-circuit emulators (ICEs). It is present,
though not documented, on some processors down to the 286, but is
only documented for the Pentium Pro. \c{INT3} is the instruction
normally used as a breakpoint by debuggers.

\b \c{INT3}, and its synonym \c{INT03}, is not precisely equivalent to
\c{INT 3}: the short form, since it is designed to be used as a
breakpoint, bypasses the normal \c{IOPL} checks in virtual-8086 mode,
and also does not go through interrupt redirection.


\S{insINTO} \i\c{INTO}: Interrupt if Overflow

\c INTO                          ; CE                   [8086]

\c{INTO} performs an \c{INT 4} software interrupt (see \k{insINT})
if and only if the overflow flag is set.


\S{insINVD} \i\c{INVD}: Invalidate Internal Caches

\c INVD                          ; 0F 08                [486]

\c{INVD} invalidates and empties the processor's internal caches,
and causes the processor to instruct external caches to do the same.
It does not write the contents of the caches back to memory first:
any modified data held in the caches will be lost. To write the data
back first, use \c{WBINVD} (\k{insWBINVD}).


\S{insINVLPG} \i\c{INVLPG}: Invalidate TLB Entry

\c INVLPG mem                    ; 0F 01 /7             [486]

\c{INVLPG} invalidates the translation lookahead buffer (TLB) entry
associated with the supplied memory address.


\S{insIRET} \i\c{IRET}, \i\c{IRETW}, \i\c{IRETD}: Return from Interrupt

\c IRET                          ; CF                   [8086]
\c IRETW                         ; o16 CF               [8086]
\c IRETD                         ; o32 CF               [386]

\c{IRET} returns from an interrupt (hardware or software) by means
of popping \c{IP} (or \c{EIP}), \c{CS} and the flags off the stack
and then continuing execution from the new \c{CS:IP}.

\c{IRETW} pops \c{IP}, \c{CS} and the flags as 2 bytes each, taking
6 bytes off the stack in total. \c{IRETD} pops \c{EIP} as 4 bytes,
pops a further 4 bytes of which the top two are discarded and the
bottom two go into \c{CS}, and pops the flags as 4 bytes as well,
taking 12 bytes off the stack.

\c{IRET} is a shorthand for either \c{IRETW} or \c{IRETD}, depending
on the default \c{BITS} setting at the time.


\S{insJcc} \i\c{Jcc}: Conditional Branch

\c Jcc imm                       ; 70+cc rb             [8086]
\c Jcc NEAR imm                  ; 0F 80+cc rw/rd       [386]

The \i{conditional jump} instructions execute a near (same segment)
jump if and only if their conditions are satisfied. For example,
\c{JNZ} jumps only if the zero flag is not set.

The ordinary form of the instructions has only a 128-byte range; the
\c{NEAR} form is a 386 extension to the instruction set, and can
span the full size of a segment. NASM will not override your choice
of jump instruction: if you want \c{Jcc NEAR}, you have to use the
\c{NEAR} keyword.

The \c{SHORT} keyword is allowed on the first form of the
instruction, for clarity, but is not necessary.

For details of the condition codes, see \k{iref-cc}.


\S{insJCXZ} \i\c{JCXZ}, \i\c{JECXZ}: Jump if CX/ECX Zero

\c JCXZ imm                      ; a16 E3 rb            [8086]
\c JECXZ imm                     ; a32 E3 rb            [386]

\c{JCXZ} performs a short jump (with maximum range 128 bytes) if and
only if the contents of the \c{CX} register is 0. \c{JECXZ} does the
same thing, but with \c{ECX}.


\S{insJMP} \i\c{JMP}: Jump

\c JMP imm                       ; E9 rw/rd             [8086]
\c JMP SHORT imm                 ; EB rb                [8086]
\c JMP imm:imm16                 ; o16 EA iw iw         [8086]
\c JMP imm:imm32                 ; o32 EA id iw         [386]
\c JMP FAR mem                   ; o16 FF /5            [8086]
\c JMP FAR mem32                 ; o32 FF /5            [386]
\c JMP r/m16                     ; o16 FF /4            [8086]
\c JMP r/m32                     ; o32 FF /4            [386]

\c{JMP} jumps to a given address. The address may be specified as an
absolute segment and offset, or as a relative jump within the
current segment.

\c{JMP SHORT imm} has a maximum range of 128 bytes, since the
displacement is specified as only 8 bits, but takes up less code
space. NASM does not choose when to generate \c{JMP SHORT} for you:
you must explicitly code \c{SHORT} every time you want a short jump.

You can choose between the two immediate \i{far jump} forms (\c{JMP
imm:imm}) by the use of the \c{WORD} and \c{DWORD} keywords: \c{JMP
WORD 0x1234:0x5678}) or \c{JMP DWORD 0x1234:0x56789abc}.

The \c{JMP FAR mem} forms execute a far jump by loading the
destination address out of memory. The address loaded consists of 16
or 32 bits of offset (depending on the operand size), and 16 bits of
segment. The operand size may be overridden using \c{JMP WORD FAR
mem} or \c{JMP DWORD FAR mem}.

The \c{JMP r/m} forms execute a \i{near jump} (within the same
segment), loading the destination address out of memory or out of a
register. The keyword \c{NEAR} may be specified, for clarity, in
these forms, but is not necessary. Again, operand size can be
overridden using \c{JMP WORD mem} or \c{JMP DWORD mem}.

As a convenience, NASM does not require you to jump to a far symbol
by coding the cumbersome \c{JMP SEG routine:routine}, but instead
allows the easier synonym \c{JMP FAR routine}.

The \c{JMP r/m} forms given above are near calls; NASM will accept
the \c{NEAR} keyword (e.g. \c{JMP NEAR [address]}), even though it
is not strictly necessary.


\S{insLAHF} \i\c{LAHF}: Load AH from Flags

\c LAHF                          ; 9F                   [8086]

\c{LAHF} sets the \c{AH} register according to the contents of the
low byte of the flags word.

The operation of \c{LAHF} is:

\c  AH <-- SF:ZF:0:AF:0:PF:1:CF

See also \c{SAHF} (\k{insSAHF}).


\S{insLAR} \i\c{LAR}: Load Access Rights

\c LAR reg16,r/m16               ; o16 0F 02 /r         [286,PRIV]
\c LAR reg32,r/m32               ; o32 0F 02 /r         [286,PRIV]

\c{LAR} takes the segment selector specified by its source (second)
operand, finds the corresponding segment descriptor in the GDT or
LDT, and loads the access-rights byte of the descriptor into its
destination (first) operand.


\S{insLDMXCSR} \i\c{LDMXCSR}: Load Streaming SIMD Extension
 Control/Status

\c LDMXCSR mem32                 ; 0F AE /2        [KATMAI,SSE]

\c{LDMXCSR} loads 32-bits of data from the specified memory location
into the \c{MXCSR} control/status register. \c{MXCSR} is used to
enable masked/unmasked exception handling, to set rounding modes,
to set flush-to-zero mode, and to view exception status flags.

For details of the \c{MXCSR} register, see the Intel processor docs.

See also \c{STMXCSR} (\k{insSTMXCSR}


\S{insLDS} \i\c{LDS}, \i\c{LES}, \i\c{LFS}, \i\c{LGS}, \i\c{LSS}: Load Far Pointer

\c LDS reg16,mem                 ; o16 C5 /r            [8086]
\c LDS reg32,mem                 ; o32 C5 /r            [386]

\c LES reg16,mem                 ; o16 C4 /r            [8086]
\c LES reg32,mem                 ; o32 C4 /r            [386]

\c LFS reg16,mem                 ; o16 0F B4 /r         [386]
\c LFS reg32,mem                 ; o32 0F B4 /r         [386]

\c LGS reg16,mem                 ; o16 0F B5 /r         [386]
\c LGS reg32,mem                 ; o32 0F B5 /r         [386]

\c LSS reg16,mem                 ; o16 0F B2 /r         [386]
\c LSS reg32,mem                 ; o32 0F B2 /r         [386]

These instructions load an entire far pointer (16 or 32 bits of
offset, plus 16 bits of segment) out of memory in one go. \c{LDS},
for example, loads 16 or 32 bits from the given memory address into
the given register (depending on the size of the register), then
loads the \e{next} 16 bits from memory into \c{DS}. \c{LES},
\c{LFS}, \c{LGS} and \c{LSS} work in the same way but use the other
segment registers.


\S{insLEA} \i\c{LEA}: Load Effective Address

\c LEA reg16,mem                 ; o16 8D /r            [8086]
\c LEA reg32,mem                 ; o32 8D /r            [386]

\c{LEA}, despite its syntax, does not access memory. It calculates
the effective address specified by its second operand as if it were
going to load or store data from it, but instead it stores the
calculated address into the register specified by its first operand.
This can be used to perform quite complex calculations (e.g. \c{LEA
EAX,[EBX+ECX*4+100]}) in one instruction.

\c{LEA}, despite being a purely arithmetic instruction which
accesses no memory, still requires square brackets around its second
operand, as if it were a memory reference.

The size of the calculation is the current \e{address} size, and the
size that the result is stored as is the current \e{operand} size.
If the address and operand size are not the same, then if the
addressing mode was 32-bits, the low 16-bits are stored, and if the
address was 16-bits, it is zero-extended to 32-bits before storing.


\S{insLEAVE} \i\c{LEAVE}: Destroy Stack Frame

\c LEAVE                         ; C9                   [186]

\c{LEAVE} destroys a stack frame of the form created by the
\c{ENTER} instruction (see \k{insENTER}). It is functionally
equivalent to \c{MOV ESP,EBP} followed by \c{POP EBP} (or \c{MOV
SP,BP} followed by \c{POP BP} in 16-bit mode).


\S{insLFENCE} \i\c{LFENCE}: Load Fence

\c LFENCE                        ; 0F AE /5        [WILLAMETTE,SSE2]

\c{LFENCE} performs a serialising operation on all loads from memory
that were issued before the \c{LFENCE} instruction. This guarantees that
all memory reads before the \c{LFENCE} instruction are visible before any
reads after the \c{LFENCE} instruction.

\c{LFENCE} is ordered respective to other \c{LFENCE} instruction, \c{MFENCE},
any memory read and any other serialising instruction (such as \c{CPUID}).

Weakly ordered memory types can be used to achieve higher processor
performance through such techniques as out-of-order issue and
speculative reads. The degree to which a consumer of data recognizes
or knows that the data is weakly ordered varies among applications
and may be unknown to the producer of this data. The \c{LFENCE}
instruction provides a performance-efficient way of ensuring load
ordering between routines that produce weakly-ordered results and
routines that consume that data.

\c{LFENCE} uses the following ModRM encoding:

\c           Mod (7:6)        = 11B
\c           Reg/Opcode (5:3) = 101B
\c           R/M (2:0)        = 000B

All other ModRM encodings are defined to be reserved, and use
of these encodings risks incompatibility with future processors.

See also \c{SFENCE} (\k{insSFENCE}) and \c{MFENCE} (\k{insMFENCE}).


\S{insLGDT} \i\c{LGDT}, \i\c{LIDT}, \i\c{LLDT}: Load Descriptor Tables

\c LGDT mem                      ; 0F 01 /2             [286,PRIV]
\c LIDT mem                      ; 0F 01 /3             [286,PRIV]
\c LLDT r/m16                    ; 0F 00 /2             [286,PRIV]

\c{LGDT} and \c{LIDT} both take a 6-byte memory area as an operand:
they load a 16-bit size limit and a 32-bit linear address from that
area (in the opposite order) into the \c{GDTR} (global descriptor table
register) or \c{IDTR} (interrupt descriptor table register). These are
the only instructions which directly use \e{linear} addresses, rather
than segment/offset pairs.

\c{LLDT} takes a segment selector as an operand. The processor looks
up that selector in the GDT and stores the limit and base address
given there into the \c{LDTR} (local descriptor table register).

See also \c{SGDT}, \c{SIDT} and \c{SLDT} (\k{insSGDT}).


\S{insLMSW} \i\c{LMSW}: Load/Store Machine Status Word

\c LMSW r/m16                    ; 0F 01 /6             [286,PRIV]

\c{LMSW} loads the bottom four bits of the source operand into the
bottom four bits of the \c{CR0} control register (or the Machine
Status Word, on 286 processors). See also \c{SMSW} (\k{insSMSW}).


\S{insLOADALL} \i\c{LOADALL}, \i\c{LOADALL286}: Load Processor State

\c LOADALL                       ; 0F 07                [386,UNDOC]
\c LOADALL286                    ; 0F 05                [286,UNDOC]

This instruction, in its two different-opcode forms, is apparently
supported on most 286 processors, some 386 and possibly some 486.
The opcode differs between the 286 and the 386.

The function of the instruction is to load all information relating
to the state of the processor out of a block of memory: on the 286,
this block is located implicitly at absolute address \c{0x800}, and
on the 386 and 486 it is at \c{[ES:EDI]}.


\S{insLODSB} \i\c{LODSB}, \i\c{LODSW}, \i\c{LODSD}: Load from String

\c LODSB                         ; AC                   [8086]
\c LODSW                         ; o16 AD               [8086]
\c LODSD                         ; o32 AD               [386]

\c{LODSB} loads a byte from \c{[DS:SI]} or \c{[DS:ESI]} into \c{AL}.
It then increments or decrements (depending on the direction flag:
increments if the flag is clear, decrements if it is set) \c{SI} or
\c{ESI}.

The register used is \c{SI} if the address size is 16 bits, and
\c{ESI} if it is 32 bits. If you need to use an address size not
equal to the current \c{BITS} setting, you can use an explicit
\i\c{a16} or \i\c{a32} prefix.

The segment register used to load from \c{[SI]} or \c{[ESI]} can be
overridden by using a segment register name as a prefix (for
example, \c{ES LODSB}).

\c{LODSW} and \c{LODSD} work in the same way, but they load a
word or a doubleword instead of a byte, and increment or decrement
the addressing registers by 2 or 4 instead of 1.


\S{insLOOP} \i\c{LOOP}, \i\c{LOOPE}, \i\c{LOOPZ}, \i\c{LOOPNE}, \i\c{LOOPNZ}: Loop with Counter

\c LOOP imm                      ; E2 rb                [8086]
\c LOOP imm,CX                   ; a16 E2 rb            [8086]
\c LOOP imm,ECX                  ; a32 E2 rb            [386]

\c LOOPE imm                     ; E1 rb                [8086]
\c LOOPE imm,CX                  ; a16 E1 rb            [8086]
\c LOOPE imm,ECX                 ; a32 E1 rb            [386]
\c LOOPZ imm                     ; E1 rb                [8086]
\c LOOPZ imm,CX                  ; a16 E1 rb            [8086]
\c LOOPZ imm,ECX                 ; a32 E1 rb            [386]

\c LOOPNE imm                    ; E0 rb                [8086]
\c LOOPNE imm,CX                 ; a16 E0 rb            [8086]
\c LOOPNE imm,ECX                ; a32 E0 rb            [386]
\c LOOPNZ imm                    ; E0 rb                [8086]
\c LOOPNZ imm,CX                 ; a16 E0 rb            [8086]
\c LOOPNZ imm,ECX                ; a32 E0 rb            [386]

\c{LOOP} decrements its counter register (either \c{CX} or \c{ECX} -
if one is not specified explicitly, the \c{BITS} setting dictates
which is used) by one, and if the counter does not become zero as a
result of this operation, it jumps to the given label. The jump has
a range of 128 bytes.

\c{LOOPE} (or its synonym \c{LOOPZ}) adds the additional condition
that it only jumps if the counter is nonzero \e{and} the zero flag
is set. Similarly, \c{LOOPNE} (and \c{LOOPNZ}) jumps only if the
counter is nonzero and the zero flag is clear.


\S{insLSL} \i\c{LSL}: Load Segment Limit

\c LSL reg16,r/m16               ; o16 0F 03 /r         [286,PRIV]
\c LSL reg32,r/m32               ; o32 0F 03 /r         [286,PRIV]

\c{LSL} is given a segment selector in its source (second) operand;
it computes the segment limit value by loading the segment limit
field from the associated segment descriptor in the \c{GDT} or \c{LDT}.
(This involves shifting left by 12 bits if the segment limit is
page-granular, and not if it is byte-granular; so you end up with a
byte limit in either case.) The segment limit obtained is then
loaded into the destination (first) operand.


\S{insLTR} \i\c{LTR}: Load Task Register

\c LTR r/m16                     ; 0F 00 /3             [286,PRIV]

\c{LTR} looks up the segment base and limit in the GDT or LDT
descriptor specified by the segment selector given as its operand,
and loads them into the Task Register.


\S{insMASKMOVDQU} \i\c{MASKMOVDQU}: Byte Mask Write

\c MASKMOVDQU xmm1,xmm2          ; 66 0F F7 /r     [WILLAMETTE,SSE2]

\c{MASKMOVDQU} stores data from xmm1 to the location specified by
\c{ES:(E)DI}. The size of the store depends on the address-size
attribute. The most significant bit in each byte of the mask
register xmm2 is used to selectively write the data (0 = no write,
1 = write) on a per-byte basis.


\S{insMASKMOVQ} \i\c{MASKMOVQ}: Byte Mask Write

\c MASKMOVQ mm1,mm2              ; 0F F7 /r        [KATMAI,MMX]

\c{MASKMOVQ} stores data from mm1 to the location specified by
\c{ES:(E)DI}. The size of the store depends on the address-size
attribute. The most significant bit in each byte of the mask
register mm2 is used to selectively write the data (0 = no write,
1 = write) on a per-byte basis.


\S{insMAXPD} \i\c{MAXPD}: Return Packed Double-Precision FP Maximum

\c MAXPD xmm1,xmm2/m128          ; 66 0F 5F /r     [WILLAMETTE,SSE2]

\c{MAXPD} performs a SIMD compare of the packed double-precision
FP numbers from xmm1 and xmm2/mem, and stores the maximum values
of each pair of values in xmm1. If the values being compared are
both zeroes, source2 (xmm2/m128) would be returned. If source2
(xmm2/m128) is an SNaN, this SNaN is forwarded unchanged to the
destination (i.e., a QNaN version of the SNaN is not returned).


\S{insMAXPS} \i\c{MAXPS}: Return Packed Single-Precision FP Maximum

\c MAXPS xmm1,xmm2/m128          ; 0F 5F /r        [KATMAI,SSE]

\c{MAXPS} performs a SIMD compare of the packed single-precision
FP numbers from xmm1 and xmm2/mem, and stores the maximum values
of each pair of values in xmm1. If the values being compared are
both zeroes, source2 (xmm2/m128) would be returned. If source2
(xmm2/m128) is an SNaN, this SNaN is forwarded unchanged to the
destination (i.e., a QNaN version of the SNaN is not returned).


\S{insMAXSD} \i\c{MAXSD}: Return Scalar Double-Precision FP Maximum

\c MAXSD xmm1,xmm2/m64           ; F2 0F 5F /r     [WILLAMETTE,SSE2]

\c{MAXSD} compares the low-order double-precision FP numbers from
xmm1 and xmm2/mem, and stores the maximum value in xmm1. If the
values being compared are both zeroes, source2 (xmm2/m64) would
be returned. If source2 (xmm2/m64) is an SNaN, this SNaN is
forwarded unchanged to the destination (i.e., a QNaN version of
the SNaN is not returned). The high quadword of the destination
is left unchanged.


\S{insMAXSS} \i\c{MAXSS}: Return Scalar Single-Precision FP Maximum

\c MAXSS xmm1,xmm2/m32           ; F3 0F 5F /r     [KATMAI,SSE]

\c{MAXSS} compares the low-order single-precision FP numbers from
xmm1 and xmm2/mem, and stores the maximum value in xmm1. If the
values being compared are both zeroes, source2 (xmm2/m32) would
be returned. If source2 (xmm2/m32) is an SNaN, this SNaN is
forwarded unchanged to the destination (i.e., a QNaN version of
the SNaN is not returned). The high three doublewords of the
destination are left unchanged.


\S{insMFENCE} \i\c{MFENCE}: Memory Fence

\c MFENCE                        ; 0F AE /6        [WILLAMETTE,SSE2]

\c{MFENCE} performs a serialising operation on all loads from memory
and writes to memory that were issued before the \c{MFENCE} instruction.
This guarantees that all memory reads and writes before the \c{MFENCE}
instruction are completed before any reads and writes after the
\c{MFENCE} instruction.

\c{MFENCE} is ordered respective to other \c{MFENCE} instructions,
\c{LFENCE}, \c{SFENCE}, any memory read and any other serialising
instruction (such as \c{CPUID}).

Weakly ordered memory types can be used to achieve higher processor
performance through such techniques as out-of-order issue, speculative
reads, write-combining, and write-collapsing. The degree to which a
consumer of data recognizes or knows that the data is weakly ordered
varies among applications and may be unknown to the producer of this
data. The \c{MFENCE} instruction provides a performance-efficient way
of ensuring load and store ordering between routines that produce
weakly-ordered results and routines that consume that data.

\c{MFENCE} uses the following ModRM encoding:

\c           Mod (7:6)        = 11B
\c           Reg/Opcode (5:3) = 110B
\c           R/M (2:0)        = 000B

All other ModRM encodings are defined to be reserved, and use
of these encodings risks incompatibility with future processors.

See also \c{LFENCE} (\k{insLFENCE}) and \c{SFENCE} (\k{insSFENCE}).


\S{insMINPD} \i\c{MINPD}: Return Packed Double-Precision FP Minimum

\c MINPD xmm1,xmm2/m128          ; 66 0F 5D /r     [WILLAMETTE,SSE2]

\c{MINPD} performs a SIMD compare of the packed double-precision
FP numbers from xmm1 and xmm2/mem, and stores the minimum values
of each pair of values in xmm1. If the values being compared are
both zeroes, source2 (xmm2/m128) would be returned. If source2
(xmm2/m128) is an SNaN, this SNaN is forwarded unchanged to the
destination (i.e., a QNaN version of the SNaN is not returned).


\S{insMINPS} \i\c{MINPS}: Return Packed Single-Precision FP Minimum

\c MINPS xmm1,xmm2/m128          ; 0F 5D /r        [KATMAI,SSE]

\c{MINPS} performs a SIMD compare of the packed single-precision
FP numbers from xmm1 and xmm2/mem, and stores the minimum values
of each pair of values in xmm1. If the values being compared are
both zeroes, source2 (xmm2/m128) would be returned. If source2
(xmm2/m128) is an SNaN, this SNaN is forwarded unchanged to the
destination (i.e., a QNaN version of the SNaN is not returned).


\S{insMINSD} \i\c{MINSD}: Return Scalar Double-Precision FP Minimum

\c MINSD xmm1,xmm2/m64           ; F2 0F 5D /r     [WILLAMETTE,SSE2]

\c{MINSD} compares the low-order double-precision FP numbers from
xmm1 and xmm2/mem, and stores the minimum value in xmm1. If the
values being compared are both zeroes, source2 (xmm2/m64) would
be returned. If source2 (xmm2/m64) is an SNaN, this SNaN is
forwarded unchanged to the destination (i.e., a QNaN version of
the SNaN is not returned). The high quadword of the destination
is left unchanged.


\S{insMINSS} \i\c{MINSS}: Return Scalar Single-Precision FP Minimum

\c MINSS xmm1,xmm2/m32           ; F3 0F 5D /r     [KATMAI,SSE]

\c{MINSS} compares the low-order single-precision FP numbers from
xmm1 and xmm2/mem, and stores the minimum value in xmm1. If the
values being compared are both zeroes, source2 (xmm2/m32) would
be returned. If source2 (xmm2/m32) is an SNaN, this SNaN is
forwarded unchanged to the destination (i.e., a QNaN version of
the SNaN is not returned). The high three doublewords of the
destination are left unchanged.


\S{insMOV} \i\c{MOV}: Move Data

\c MOV r/m8,reg8                 ; 88 /r                [8086]
\c MOV r/m16,reg16               ; o16 89 /r            [8086]
\c MOV r/m32,reg32               ; o32 89 /r            [386]
\c MOV reg8,r/m8                 ; 8A /r                [8086]
\c MOV reg16,r/m16               ; o16 8B /r            [8086]
\c MOV reg32,r/m32               ; o32 8B /r            [386]

\c MOV reg8,imm8                 ; B0+r ib              [8086]
\c MOV reg16,imm16               ; o16 B8+r iw          [8086]
\c MOV reg32,imm32               ; o32 B8+r id          [386]
\c MOV r/m8,imm8                 ; C6 /0 ib             [8086]
\c MOV r/m16,imm16               ; o16 C7 /0 iw         [8086]
\c MOV r/m32,imm32               ; o32 C7 /0 id         [386]

\c MOV AL,memoffs8               ; A0 ow/od             [8086]
\c MOV AX,memoffs16              ; o16 A1 ow/od         [8086]
\c MOV EAX,memoffs32             ; o32 A1 ow/od         [386]
\c MOV memoffs8,AL               ; A2 ow/od             [8086]
\c MOV memoffs16,AX              ; o16 A3 ow/od         [8086]
\c MOV memoffs32,EAX             ; o32 A3 ow/od         [386]

\c MOV r/m16,segreg              ; o16 8C /r            [8086]
\c MOV r/m32,segreg              ; o32 8C /r            [386]
\c MOV segreg,r/m16              ; o16 8E /r            [8086]
\c MOV segreg,r/m32              ; o32 8E /r            [386]

\c MOV reg32,CR0/2/3/4           ; 0F 20 /r             [386]
\c MOV reg32,DR0/1/2/3/6/7       ; 0F 21 /r             [386]
\c MOV reg32,TR3/4/5/6/7         ; 0F 24 /r             [386]
\c MOV CR0/2/3/4,reg32           ; 0F 22 /r             [386]
\c MOV DR0/1/2/3/6/7,reg32       ; 0F 23 /r             [386]
\c MOV TR3/4/5/6/7,reg32         ; 0F 26 /r             [386]

\c{MOV} copies the contents of its source (second) operand into its
destination (first) operand.

In all forms of the \c{MOV} instruction, the two operands are the
same size, except for moving between a segment register and an
\c{r/m32} operand. These instructions are treated exactly like the
corresponding 16-bit equivalent (so that, for example, \c{MOV
DS,EAX} functions identically to \c{MOV DS,AX} but saves a prefix
when in 32-bit mode), except that when a segment register is moved
into a 32-bit destination, the top two bytes of the result are
undefined.

\c{MOV} may not use \c{CS} as a destination.

\c{CR4} is only a supported register on the Pentium and above.

Test registers are supported on 386/486 processors and on some
non-Intel Pentium class processors.


\S{insMOVAPD} \i\c{MOVAPD}: Move Aligned Packed Double-Precision FP Values

\c MOVAPD xmm1,xmm2/mem128       ; 66 0F 28 /r     [WILLAMETTE,SSE2]
\c MOVAPD xmm1/mem128,xmm2       ; 66 0F 29 /r     [WILLAMETTE,SSE2]

\c{MOVAPD} moves a double quadword containing 2 packed double-precision
FP values from the source operand to the destination. When the source
or destination operand is a memory location, it must be aligned on a
16-byte boundary.

To move data in and out of memory locations that are not known to be on
16-byte boundaries, use the \c{MOVUPD} instruction (\k{insMOVUPD}).


\S{insMOVAPS} \i\c{MOVAPS}: Move Aligned Packed Single-Precision FP Values

\c MOVAPS xmm1,xmm2/mem128       ; 0F 28 /r        [KATMAI,SSE]
\c MOVAPS xmm1/mem128,xmm2       ; 0F 29 /r        [KATMAI,SSE]

\c{MOVAPS} moves a double quadword containing 4 packed single-precision
FP values from the source operand to the destination. When the source
or destination operand is a memory location, it must be aligned on a
16-byte boundary.

To move data in and out of memory locations that are not known to be on
16-byte boundaries, use the \c{MOVUPS} instruction (\k{insMOVUPS}).


\S{insMOVD} \i\c{MOVD}: Move Doubleword to/from MMX Register

\c MOVD mm,r/m32                 ; 0F 6E /r             [PENT,MMX]
\c MOVD r/m32,mm                 ; 0F 7E /r             [PENT,MMX]
\c MOVD xmm,r/m32                ; 66 0F 6E /r     [WILLAMETTE,SSE2]
\c MOVD r/m32,xmm                ; 66 0F 7E /r     [WILLAMETTE,SSE2]

\c{MOVD} copies 32 bits from its source (second) operand into its
destination (first) operand. When the destination is a 64-bit \c{MMX}
register or a 128-bit \c{XMM} register, the input value is zero-extended
to fill the destination register.


\S{insMOVDQ2Q} \i\c{MOVDQ2Q}: Move Quadword from XMM to MMX register.

\c MOVDQ2Q mm,xmm                ; F2 OF D6 /r     [WILLAMETTE,SSE2]

\c{MOVDQ2Q} moves the low quadword from the source operand to the
destination operand.


\S{insMOVDQA} \i\c{MOVDQA}: Move Aligned Double Quadword

\c MOVDQA xmm1,xmm2/m128         ; 66 OF 6F /r     [WILLAMETTE,SSE2]
\c MOVDQA xmm1/m128,xmm2         ; 66 OF 7F /r     [WILLAMETTE,SSE2]

\c{MOVDQA} moves a double quadword from the source operand to the
destination operand. When the source or destination operand is a
memory location, it must be aligned to a 16-byte boundary.

To move a double quadword to or from unaligned memory locations,
use the \c{MOVDQU} instruction (\k{insMOVDQU}).


\S{insMOVDQU} \i\c{MOVDQU}: Move Unaligned Double Quadword

\c MOVDQU xmm1,xmm2/m128         ; F3 OF 6F /r     [WILLAMETTE,SSE2]
\c MOVDQU xmm1/m128,xmm2         ; F3 OF 7F /r     [WILLAMETTE,SSE2]

\c{MOVDQU} moves a double quadword from the source operand to the
destination operand. When the source or destination operand is a
memory location, the memory may be unaligned.

To move a double quadword to or from known aligned memory locations,
use the \c{MOVDQA} instruction (\k{insMOVDQA}).


\S{insMOVHLPS} \i\c{MOVHLPS}: Move Packed Single-Precision FP High to Low

\c MOVHLPS xmm1,xmm2             ; OF 12 /r        [KATMAI,SSE]

\c{MOVHLPS} moves the two packed single-precision FP values from the
high quadword of the source register xmm2 to the low quadword of the
destination register, xmm2. The upper quadword of xmm1 is left unchanged.

The operation of this instruction is:

\c    dst[0-63]   := src[64-127],
\c    dst[64-127] remains unchanged.


\S{insMOVHPD} \i\c{MOVHPD}: Move High Packed Double-Precision FP

\c MOVHPD xmm,m64               ; 66 OF 16 /r      [WILLAMETTE,SSE2]
\c MOVHPD m64,xmm               ; 66 OF 17 /r      [WILLAMETTE,SSE2]

\c{MOVHPD} moves a double-precision FP value between the source and
destination operands. One of the operands is a 64-bit memory location,
the other is the high quadword of an \c{XMM} register.

The operation of this instruction is:

\c    mem[0-63]   := xmm[64-127];

or

\c    xmm[0-63]   remains unchanged;
\c    xmm[64-127] := mem[0-63].


\S{insMOVHPS} \i\c{MOVHPS}: Move High Packed Single-Precision FP

\c MOVHPS xmm,m64               ; 0F 16 /r         [KATMAI,SSE]
\c MOVHPS m64,xmm               ; 0F 17 /r         [KATMAI,SSE]

\c{MOVHPS} moves two packed single-precision FP values between the source
and destination operands. One of the operands is a 64-bit memory location,
the other is the high quadword of an \c{XMM} register.

The operation of this instruction is:

\c    mem[0-63]   := xmm[64-127];

or

\c    xmm[0-63]   remains unchanged;
\c    xmm[64-127] := mem[0-63].


\S{insMOVLHPS} \i\c{MOVLHPS}: Move Packed Single-Precision FP Low to High

\c MOVLHPS xmm1,xmm2             ; OF 16 /r         [KATMAI,SSE]

\c{MOVLHPS} moves the two packed single-precision FP values from the
low quadword of the source register xmm2 to the high quadword of the
destination register, xmm2. The low quadword of xmm1 is left unchanged.

The operation of this instruction is:

\c    dst[0-63]   remains unchanged;
\c    dst[64-127] := src[0-63].

\S{insMOVLPD} \i\c{MOVLPD}: Move Low Packed Double-Precision FP

\c MOVLPD xmm,m64                ; 66 OF 12 /r     [WILLAMETTE,SSE2]
\c MOVLPD m64,xmm                ; 66 OF 13 /r     [WILLAMETTE,SSE2]

\c{MOVLPD} moves a double-precision FP value between the source and
destination operands. One of the operands is a 64-bit memory location,
the other is the low quadword of an \c{XMM} register.

The operation of this instruction is:

\c    mem(0-63)   := xmm(0-63);

or

\c    xmm(0-63)   := mem(0-63);
\c    xmm(64-127) remains unchanged.

\S{insMOVLPS} \i\c{MOVLPS}: Move Low Packed Single-Precision FP

\c MOVLPS xmm,m64                ; OF 12 /r        [KATMAI,SSE]
\c MOVLPS m64,xmm                ; OF 13 /r        [KATMAI,SSE]

\c{MOVLPS} moves two packed single-precision FP values between the source
and destination operands. One of the operands is a 64-bit memory location,
the other is the low quadword of an \c{XMM} register.

The operation of this instruction is:

\c    mem(0-63)   := xmm(0-63);

or

\c    xmm(0-63)   := mem(0-63);
\c    xmm(64-127) remains unchanged.


\S{insMOVMSKPD} \i\c{MOVMSKPD}: Extract Packed Double-Precision FP Sign Mask

\c MOVMSKPD reg32,xmm              ; 66 0F 50 /r   [WILLAMETTE,SSE2]

\c{MOVMSKPD} inserts a 2-bit mask in r32, formed of the most significant
bits of each double-precision FP number of the source operand.


\S{insMOVMSKPS} \i\c{MOVMSKPS}: Extract Packed Single-Precision FP Sign Mask

\c MOVMSKPS reg32,xmm              ; 0F 50 /r      [KATMAI,SSE]

\c{MOVMSKPS} inserts a 4-bit mask in r32, formed of the most significant
bits of each single-precision FP number of the source operand.


\S{insMOVNTDQ} \i\c{MOVNTDQ}: Move Double Quadword Non Temporal

\c MOVNTDQ m128,xmm              ; 66 0F E7 /r     [WILLAMETTE,SSE2]

\c{MOVNTDQ} moves the double quadword from the \c{XMM} source
register to the destination memory location, using a non-temporal
hint. This store instruction minimizes cache pollution.


\S{insMOVNTI} \i\c{MOVNTI}: Move Doubleword Non Temporal

\c MOVNTI m32,reg32              ; 0F C3 /r        [WILLAMETTE,SSE2]

\c{MOVNTI} moves the doubleword in the source register
to the destination memory location, using a non-temporal
hint. This store instruction minimizes cache pollution.


\S{insMOVNTPD} \i\c{MOVNTPD}: Move Aligned Four Packed Single-Precision
FP Values Non Temporal

\c MOVNTPD m128,xmm              ; 66 0F 2B /r     [WILLAMETTE,SSE2]

\c{MOVNTPD} moves the double quadword from the \c{XMM} source
register to the destination memory location, using a non-temporal
hint. This store instruction minimizes cache pollution. The memory
location must be aligned to a 16-byte boundary.


\S{insMOVNTPS} \i\c{MOVNTPS}: Move Aligned Four Packed Single-Precision
FP Values Non Temporal

\c MOVNTPS m128,xmm              ; 0F 2B /r        [KATMAI,SSE]

\c{MOVNTPS} moves the double quadword from the \c{XMM} source
register to the destination memory location, using a non-temporal
hint. This store instruction minimizes cache pollution. The memory
location must be aligned to a 16-byte boundary.


\S{insMOVNTQ} \i\c{MOVNTQ}: Move Quadword Non Temporal

\c MOVNTQ m64,mm                 ; 0F E7 /r        [KATMAI,MMX]

\c{MOVNTQ} moves the quadword in the \c{MMX} source register
to the destination memory location, using a non-temporal
hint. This store instruction minimizes cache pollution.


\S{insMOVQ} \i\c{MOVQ}: Move Quadword to/from MMX Register

\c MOVQ mm1,mm2/m64               ; 0F 6F /r             [PENT,MMX]
\c MOVQ mm1/m64,mm2               ; 0F 7F /r             [PENT,MMX]

\c MOVQ xmm1,xmm2/m64             ; F3 0F 7E /r    [WILLAMETTE,SSE2]
\c MOVQ xmm1/m64,xmm2             ; 66 0F D6 /r    [WILLAMETTE,SSE2]

\c{MOVQ} copies 64 bits from its source (second) operand into its
destination (first) operand. When the source is an \c{XMM} register,
the low quadword is moved. When the destination is an \c{XMM} register,
the destination is the low quadword, and the high quadword is cleared.


\S{insMOVQ2DQ} \i\c{MOVQ2DQ}: Move Quadword from MMX to XMM register.

\c MOVQ2DQ xmm,mm                ; F3 OF D6 /r     [WILLAMETTE,SSE2]

\c{MOVQ2DQ} moves the quadword from the source operand to the low
quadword of the destination operand, and clears the high quadword.


\S{insMOVSB} \i\c{MOVSB}, \i\c{MOVSW}, \i\c{MOVSD}: Move String

\c MOVSB                         ; A4                   [8086]
\c MOVSW                         ; o16 A5               [8086]
\c MOVSD                         ; o32 A5               [386]

\c{MOVSB} copies the byte at \c{[DS:SI]} or \c{[DS:ESI]} to
\c{[ES:DI]} or \c{[ES:EDI]}. It then increments or decrements
(depending on the direction flag: increments if the flag is clear,
decrements if it is set) \c{SI} and \c{DI} (or \c{ESI} and \c{EDI}).

The registers used are \c{SI} and \c{DI} if the address size is 16
bits, and \c{ESI} and \c{EDI} if it is 32 bits. If you need to use
an address size not equal to the current \c{BITS} setting, you can
use an explicit \i\c{a16} or \i\c{a32} prefix.

The segment register used to load from \c{[SI]} or \c{[ESI]} can be
overridden by using a segment register name as a prefix (for
example, \c{es movsb}). The use of \c{ES} for the store to \c{[DI]}
or \c{[EDI]} cannot be overridden.

\c{MOVSW} and \c{MOVSD} work in the same way, but they copy a word
or a doubleword instead of a byte, and increment or decrement the
addressing registers by 2 or 4 instead of 1.

The \c{REP} prefix may be used to repeat the instruction \c{CX} (or
\c{ECX} - again, the address size chooses which) times.


\S{insMOVSD} \i\c{MOVSD}: Move Scalar Double-Precision FP Value

\c MOVSD xmm1,xmm2/m64           ; F2 0F 10 /r     [WILLAMETTE,SSE2]
\c MOVSD xmm1/m64,xmm2           ; F2 0F 11 /r     [WILLAMETTE,SSE2]

\c{MOVSD} moves a double-precision FP value from the source operand
to the destination operand. When the source or destination is a
register, the low-order FP value is read or written.


\S{insMOVSS} \i\c{MOVSS}: Move Scalar Single-Precision FP Value

\c MOVSS xmm1,xmm2/m32           ; F3 0F 10 /r     [KATMAI,SSE]
\c MOVSS xmm1/m32,xmm2           ; F3 0F 11 /r     [KATMAI,SSE]

\c{MOVSS} moves a single-precision FP value from the source operand
to the destination operand. When the source or destination is a
register, the low-order FP value is read or written.


\S{insMOVSX} \i\c{MOVSX}, \i\c{MOVZX}: Move Data with Sign or Zero Extend

\c MOVSX reg16,r/m8              ; o16 0F BE /r         [386]
\c MOVSX reg32,r/m8              ; o32 0F BE /r         [386]
\c MOVSX reg32,r/m16             ; o32 0F BF /r         [386]

\c MOVZX reg16,r/m8              ; o16 0F B6 /r         [386]
\c MOVZX reg32,r/m8              ; o32 0F B6 /r         [386]
\c MOVZX reg32,r/m16             ; o32 0F B7 /r         [386]

\c{MOVSX} sign-extends its source (second) operand to the length of
its destination (first) operand, and copies the result into the
destination operand. \c{MOVZX} does the same, but zero-extends
rather than sign-extending.


\S{insMOVUPD} \i\c{MOVUPD}: Move Unaligned Packed Double-Precision FP Values

\c MOVUPD xmm1,xmm2/mem128       ; 66 0F 10 /r     [WILLAMETTE,SSE2]
\c MOVUPD xmm1/mem128,xmm2       ; 66 0F 11 /r     [WILLAMETTE,SSE2]

\c{MOVUPD} moves a double quadword containing 2 packed double-precision
FP values from the source operand to the destination. This instruction
makes no assumptions about alignment of memory operands.

To move data in and out of memory locations that are known to be on 16-byte
boundaries, use the \c{MOVAPD} instruction (\k{insMOVAPD}).


\S{insMOVUPS} \i\c{MOVUPS}: Move Unaligned Packed Single-Precision FP Values

\c MOVUPS xmm1,xmm2/mem128       ; 0F 10 /r        [KATMAI,SSE]
\c MOVUPS xmm1/mem128,xmm2       ; 0F 11 /r        [KATMAI,SSE]

\c{MOVUPS} moves a double quadword containing 4 packed single-precision
FP values from the source operand to the destination. This instruction
makes no assumptions about alignment of memory operands.

To move data in and out of memory locations that are known to be on 16-byte
boundaries, use the \c{MOVAPS} instruction (\k{insMOVAPS}).


\S{insMUL} \i\c{MUL}: Unsigned Integer Multiply

\c MUL r/m8                      ; F6 /4                [8086]
\c MUL r/m16                     ; o16 F7 /4            [8086]
\c MUL r/m32                     ; o32 F7 /4            [386]

\c{MUL} performs unsigned integer multiplication. The other operand
to the multiplication, and the destination operand, are implicit, in
the following way:

\b For \c{MUL r/m8}, \c{AL} is multiplied by the given operand; the
product is stored in \c{AX}.

\b For \c{MUL r/m16}, \c{AX} is multiplied by the given operand;
the product is stored in \c{DX:AX}.

\b For \c{MUL r/m32}, \c{EAX} is multiplied by the given operand;
the product is stored in \c{EDX:EAX}.

Signed integer multiplication is performed by the \c{IMUL}
instruction: see \k{insIMUL}.


\S{insMULPD} \i\c{MULPD}: Packed Single-FP Multiply

\c MULPD xmm1,xmm2/mem128        ; 66 0F 59 /r     [WILLAMETTE,SSE2]

\c{MULPD} performs a SIMD multiply of the packed double-precision FP
values in both operands, and stores the results in the destination register.


\S{insMULPS} \i\c{MULPS}: Packed Single-FP Multiply

\c MULPS xmm1,xmm2/mem128        ; 0F 59 /r        [KATMAI,SSE]

\c{MULPS} performs a SIMD multiply of the packed single-precision FP
values in both operands, and stores the results in the destination register.


\S{insMULSD} \i\c{MULSD}: Scalar Single-FP Multiply

\c MULSD xmm1,xmm2/mem32         ; F2 0F 59 /r     [WILLAMETTE,SSE2]

\c{MULSD} multiplies the lowest double-precision FP values of both
operands, and stores the result in the low quadword of xmm1.


\S{insMULSS} \i\c{MULSS}: Scalar Single-FP Multiply

\c MULSS xmm1,xmm2/mem32         ; F3 0F 59 /r     [KATMAI,SSE]

\c{MULSS} multiplies the lowest single-precision FP values of both
operands, and stores the result in the low doubleword of xmm1.


\S{insNEG} \i\c{NEG}, \i\c{NOT}: Two's and One's Complement

\c NEG r/m8                      ; F6 /3                [8086]
\c NEG r/m16                     ; o16 F7 /3            [8086]
\c NEG r/m32                     ; o32 F7 /3            [386]

\c NOT r/m8                      ; F6 /2                [8086]
\c NOT r/m16                     ; o16 F7 /2            [8086]
\c NOT r/m32                     ; o32 F7 /2            [386]

\c{NEG} replaces the contents of its operand by the two's complement
negation (invert all the bits and then add one) of the original
value. \c{NOT}, similarly, performs one's complement (inverts all
the bits).


\S{insNOP} \i\c{NOP}: No Operation

\c NOP                           ; 90                   [8086]

\c{NOP} performs no operation. Its opcode is the same as that
generated by \c{XCHG AX,AX} or \c{XCHG EAX,EAX} (depending on the
processor mode; see \k{insXCHG}).


\S{insOR} \i\c{OR}: Bitwise OR

\c OR r/m8,reg8                  ; 08 /r                [8086]
\c OR r/m16,reg16                ; o16 09 /r            [8086]
\c OR r/m32,reg32                ; o32 09 /r            [386]

\c OR reg8,r/m8                  ; 0A /r                [8086]
\c OR reg16,r/m16                ; o16 0B /r            [8086]
\c OR reg32,r/m32                ; o32 0B /r            [386]

\c OR r/m8,imm8                  ; 80 /1 ib             [8086]
\c OR r/m16,imm16                ; o16 81 /1 iw         [8086]
\c OR r/m32,imm32                ; o32 81 /1 id         [386]

\c OR r/m16,imm8                 ; o16 83 /1 ib         [8086]
\c OR r/m32,imm8                 ; o32 83 /1 ib         [386]

\c OR AL,imm8                    ; 0C ib                [8086]
\c OR AX,imm16                   ; o16 0D iw            [8086]
\c OR EAX,imm32                  ; o32 0D id            [386]

\c{OR} performs a bitwise OR operation between its two operands
(i.e. each bit of the result is 1 if and only if at least one of the
corresponding bits of the two inputs was 1), and stores the result
in the destination (first) operand.

In the forms with an 8-bit immediate second operand and a longer
first operand, the second operand is considered to be signed, and is
sign-extended to the length of the first operand. In these cases,
the \c{BYTE} qualifier is necessary to force NASM to generate this
form of the instruction.

The MMX instruction \c{POR} (see \k{insPOR}) performs the same
operation on the 64-bit MMX registers.


\S{insORPD} \i\c{ORPD}: Bit-wise Logical OR of Double-Precision FP Data

\c ORPD xmm1,xmm2/m128           ; 66 0F 56 /r     [WILLAMETTE,SSE2]

\c{ORPD} return a bit-wise logical OR between xmm1 and xmm2/mem,
and stores the result in xmm1. If the source operand is a memory
location, it must be aligned to a 16-byte boundary.


\S{insORPS} \i\c{ORPS}: Bit-wise Logical OR of Single-Precision FP Data

\c ORPS xmm1,xmm2/m128           ; 0F 56 /r        [KATMAI,SSE]

\c{ORPS} return a bit-wise logical OR between xmm1 and xmm2/mem,
and stores the result in xmm1. If the source operand is a memory
location, it must be aligned to a 16-byte boundary.


\S{insOUT} \i\c{OUT}: Output Data to I/O Port

\c OUT imm8,AL                   ; E6 ib                [8086]
\c OUT imm8,AX                   ; o16 E7 ib            [8086]
\c OUT imm8,EAX                  ; o32 E7 ib            [386]
\c OUT DX,AL                     ; EE                   [8086]
\c OUT DX,AX                     ; o16 EF               [8086]
\c OUT DX,EAX                    ; o32 EF               [386]

\c{OUT} writes the contents of the given source register to the
specified I/O port. The port number may be specified as an immediate
value if it is between 0 and 255, and otherwise must be stored in
\c{DX}. See also \c{IN} (\k{insIN}).


\S{insOUTSB} \i\c{OUTSB}, \i\c{OUTSW}, \i\c{OUTSD}: Output String to I/O Port

\c OUTSB                         ; 6E                   [186]
\c OUTSW                         ; o16 6F               [186]
\c OUTSD                         ; o32 6F               [386]

\c{OUTSB} loads a byte from \c{[DS:SI]} or \c{[DS:ESI]} and writes
it to the I/O port specified in \c{DX}. It then increments or
decrements (depending on the direction flag: increments if the flag
is clear, decrements if it is set) \c{SI} or \c{ESI}.

The register used is \c{SI} if the address size is 16 bits, and
\c{ESI} if it is 32 bits. If you need to use an address size not
equal to the current \c{BITS} setting, you can use an explicit
\i\c{a16} or \i\c{a32} prefix.

The segment register used to load from \c{[SI]} or \c{[ESI]} can be
overridden by using a segment register name as a prefix (for
example, \c{es outsb}).

\c{OUTSW} and \c{OUTSD} work in the same way, but they output a
word or a doubleword instead of a byte, and increment or decrement
the addressing registers by 2 or 4 instead of 1.

The \c{REP} prefix may be used to repeat the instruction \c{CX} (or
\c{ECX} - again, the address size chooses which) times.


\S{insPACKSSDW} \i\c{PACKSSDW}, \i\c{PACKSSWB}, \i\c{PACKUSWB}: Pack Data

\c PACKSSDW mm1,mm2/m64          ; 0F 6B /r             [PENT,MMX]
\c PACKSSWB mm1,mm2/m64          ; 0F 63 /r             [PENT,MMX]
\c PACKUSWB mm1,mm2/m64          ; 0F 67 /r             [PENT,MMX]

\c PACKSSDW xmm1,xmm2/m128       ; 66 0F 6B /r     [WILLAMETTE,SSE2]
\c PACKSSWB xmm1,xmm2/m128       ; 66 0F 63 /r     [WILLAMETTE,SSE2]
\c PACKUSWB xmm1,xmm2/m128       ; 66 0F 67 /r     [WILLAMETTE,SSE2]

All these instructions start by combining the source and destination
operands, and then splitting the result in smaller sections which it
then packs into the destination register. The \c{MMX} versions pack
two 64-bit operands into one 64-bit register, while the \c{SSE}
versions pack two 128-bit operands into one 128-bit register.

\b \c{PACKSSWB} splits the combined value into words, and then reduces
the words to bytes, using signed saturation. It then packs the bytes
into the destination register in the same order the words were in.

\b \c{PACKSSDW} performs the same operation as \c{PACKSSWB}, except that
it reduces doublewords to words, then packs them into the destination
register.

\b \c{PACKUSWB} performs the same operation as \c{PACKSSWB}, except that
it uses unsigned saturation when reducing the size of the elements.

To perform signed saturation on a number, it is replaced by the largest
signed number (\c{7FFFh} or \c{7Fh}) that \e{will} fit, and if it is too
small it is replaced by the smallest signed number (\c{8000h} or
\c{80h}) that will fit. To perform unsigned saturation, the input is
treated as unsigned, and the input is replaced by the largest unsigned
number that will fit.


\S{insPADDB} \i\c{PADDB}, \i\c{PADDW}, \i\c{PADDD}: Add Packed Integers

\c PADDB mm1,mm2/m64             ; 0F FC /r             [PENT,MMX]
\c PADDW mm1,mm2/m64             ; 0F FD /r             [PENT,MMX]
\c PADDD mm1,mm2/m64             ; 0F FE /r             [PENT,MMX]

\c PADDB xmm1,xmm2/m128          ; 66 0F FC /r     [WILLAMETTE,SSE2]
\c PADDW xmm1,xmm2/m128          ; 66 0F FD /r     [WILLAMETTE,SSE2]
\c PADDD xmm1,xmm2/m128          ; 66 0F FE /r     [WILLAMETTE,SSE2]

\c{PADDx} performs packed addition of the two operands, storing the
result in the destination (first) operand.

\b \c{PADDB} treats the operands as packed bytes, and adds each byte
individually;

\b \c{PADDW} treats the operands as packed words;

\b \c{PADDD} treats its operands as packed doublewords.

When an individual result is too large to fit in its destination, it
is wrapped around and the low bits are stored, with the carry bit
discarded.


\S{insPADDQ} \i\c{PADDQ}: Add Packed Quadword Integers

\c PADDQ mm1,mm2/m64             ; 0F D4 /r             [PENT,MMX]

\c PADDQ xmm1,xmm2/m128          ; 66 0F D4 /r     [WILLAMETTE,SSE2]

\c{PADDQ} adds the quadwords in the source and destination operands, and
stores the result in the destination register.

When an individual result is too large to fit in its destination, it
is wrapped around and the low bits are stored, with the carry bit
discarded.


\S{insPADDSB} \i\c{PADDSB}, \i\c{PADDSW}: Add Packed Signed Integers With Saturation

\c PADDSB mm1,mm2/m64            ; 0F EC /r             [PENT,MMX]
\c PADDSW mm1,mm2/m64            ; 0F ED /r             [PENT,MMX]

\c PADDSB xmm1,xmm2/m128         ; 66 0F EC /r     [WILLAMETTE,SSE2]
\c PADDSW xmm1,xmm2/m128         ; 66 0F ED /r     [WILLAMETTE,SSE2]

\c{PADDSx} performs packed addition of the two operands, storing the
result in the destination (first) operand.
\c{PADDSB} treats the operands as packed bytes, and adds each byte
individually; and \c{PADDSW} treats the operands as packed words.

When an individual result is too large to fit in its destination, a
saturated value is stored. The resulting value is the value with the
largest magnitude of the same sign as the result which will fit in
the available space.


\S{insPADDSIW} \i\c{PADDSIW}: MMX Packed Addition to Implicit Destination

\c PADDSIW mmxreg,r/m64          ; 0F 51 /r             [CYRIX,MMX]

\c{PADDSIW}, specific to the Cyrix extensions to the MMX instruction
set, performs the same function as \c{PADDSW}, except that the result
is placed in an implied register.

To work out the implied register, invert the lowest bit in the register
number. So \c{PADDSIW MM0,MM2} would put the result in \c{MM1}, but
\c{PADDSIW MM1,MM2} would put the result in \c{MM0}.


\S{insPADDUSB} \i\c{PADDUSB}, \i\c{PADDUSW}: Add Packed Unsigned Integers With Saturation

\c PADDUSB mm1,mm2/m64           ; 0F DC /r             [PENT,MMX]
\c PADDUSW mm1,mm2/m64           ; 0F DD /r             [PENT,MMX]

\c PADDUSB xmm1,xmm2/m128         ; 66 0F DC /r    [WILLAMETTE,SSE2]
\c PADDUSW xmm1,xmm2/m128         ; 66 0F DD /r    [WILLAMETTE,SSE2]

\c{PADDUSx} performs packed addition of the two operands, storing the
result in the destination (first) operand.
\c{PADDUSB} treats the operands as packed bytes, and adds each byte
individually; and \c{PADDUSW} treats the operands as packed words.

When an individual result is too large to fit in its destination, a
saturated value is stored. The resulting value is the maximum value
that will fit in the available space.


\S{insPAND} \i\c{PAND}, \i\c{PANDN}: MMX Bitwise AND and AND-NOT

\c PAND mm1,mm2/m64              ; 0F DB /r             [PENT,MMX]
\c PANDN mm1,mm2/m64             ; 0F DF /r             [PENT,MMX]

\c PAND xmm1,xmm2/m128           ; 66 0F DB /r     [WILLAMETTE,SSE2]
\c PANDN xmm1,xmm2/m128          ; 66 0F DF /r     [WILLAMETTE,SSE2]


\c{PAND} performs a bitwise AND operation between its two operands
(i.e. each bit of the result is 1 if and only if the corresponding
bits of the two inputs were both 1), and stores the result in the
destination (first) operand.

\c{PANDN} performs the same operation, but performs a one's
complement operation on the destination (first) operand first.


\S{insPAUSE} \i\c{PAUSE}: Spin Loop Hint

\c PAUSE                         ; F3 90           [WILLAMETTE,SSE2]

\c{PAUSE} provides a hint to the processor that the following code
is a spin loop. This improves processor performance by bypassing
possible memory order violations. On older processors, this instruction
operates as a \c{NOP}.


\S{insPAVEB} \i\c{PAVEB}: MMX Packed Average

\c PAVEB mmxreg,r/m64            ; 0F 50 /r             [CYRIX,MMX]

\c{PAVEB}, specific to the Cyrix MMX extensions, treats its two
operands as vectors of eight unsigned bytes, and calculates the
average of the corresponding bytes in the operands. The resulting
vector of eight averages is stored in the first operand.

This opcode maps to \c{MOVMSKPS r32, xmm} on processors that support
the SSE instruction set.


\S{insPAVGB} \i\c{PAVGB} \i\c{PAVGW}: Average Packed Integers

\c PAVGB mm1,mm2/m64             ; 0F E0 /r        [KATMAI,MMX]
\c PAVGW mm1,mm2/m64             ; 0F E3 /r        [KATMAI,MMX,SM]

\c PAVGB xmm1,xmm2/m128          ; 66 0F E0 /r     [WILLAMETTE,SSE2]
\c PAVGW xmm1,xmm2/m128          ; 66 0F E3 /r     [WILLAMETTE,SSE2]

\c{PAVGB} and \c{PAVGW} add the unsigned data elements of the source
operand to the unsigned data elements of the destination register,
then adds 1 to the temporary results. The results of the add are then
each independently right-shifted by one bit position. The high order
bits of each element are filled with the carry bits of the corresponding
sum.

\b \c{PAVGB} operates on packed unsigned bytes, and

\b \c{PAVGW} operates on packed unsigned words.


\S{insPAVGUSB} \i\c{PAVGUSB}: Average of unsigned packed 8-bit values

\c PAVGUSB mm1,mm2/m64           ; 0F 0F /r BF          [PENT,3DNOW]

\c{PAVGUSB} adds the unsigned data elements of the source operand to
the unsigned data elements of the destination register, then adds 1
to the temporary results. The results of the add are then each
independently right-shifted by one bit position. The high order bits
of each element are filled with the carry bits of the corresponding
sum.

This instruction performs exactly the same operations as the \c{PAVGB}
\c{MMX} instruction (\k{insPAVGB}).


\S{insPCMPEQB} \i\c{PCMPxx}: Compare Packed Integers.

\c PCMPEQB mm1,mm2/m64           ; 0F 74 /r             [PENT,MMX]
\c PCMPEQW mm1,mm2/m64           ; 0F 75 /r             [PENT,MMX]
\c PCMPEQD mm1,mm2/m64           ; 0F 76 /r             [PENT,MMX]

\c PCMPGTB mm1,mm2/m64           ; 0F 64 /r             [PENT,MMX]
\c PCMPGTW mm1,mm2/m64           ; 0F 65 /r             [PENT,MMX]
\c PCMPGTD mm1,mm2/m64           ; 0F 66 /r             [PENT,MMX]

\c PCMPEQB xmm1,xmm2/m128        ; 66 0F 74 /r     [WILLAMETTE,SSE2]
\c PCMPEQW xmm1,xmm2/m128        ; 66 0F 75 /r     [WILLAMETTE,SSE2]
\c PCMPEQD xmm1,xmm2/m128        ; 66 0F 76 /r     [WILLAMETTE,SSE2]

\c PCMPGTB xmm1,xmm2/m128        ; 66 0F 64 /r     [WILLAMETTE,SSE2]
\c PCMPGTW xmm1,xmm2/m128        ; 66 0F 65 /r     [WILLAMETTE,SSE2]
\c PCMPGTD xmm1,xmm2/m128        ; 66 0F 66 /r     [WILLAMETTE,SSE2]

The \c{PCMPxx} instructions all treat their operands as vectors of
bytes, words, or doublewords; corresponding elements of the source
and destination are compared, and the corresponding element of the
destination (first) operand is set to all zeros or all ones
depending on the result of the comparison.

\b \c{PCMPxxB} treats the operands as vectors of bytes;

\b \c{PCMPxxW} treats the operands as vectors of words;

\b \c{PCMPxxD} treats the operands as vectors of doublewords;

\b \c{PCMPEQx} sets the corresponding element of the destination
operand to all ones if the two elements compared are equal;

\b \c{PCMPGTx} sets the destination element to all ones if the element
of the first (destination) operand is greater (treated as a signed
integer) than that of the second (source) operand.


\S{insPDISTIB} \i\c{PDISTIB}: MMX Packed Distance and Accumulate
with Implied Register

\c PDISTIB mm,m64                ; 0F 54 /r             [CYRIX,MMX]

\c{PDISTIB}, specific to the Cyrix MMX extensions, treats its two
input operands as vectors of eight unsigned bytes. For each byte
position, it finds the absolute difference between the bytes in that
position in the two input operands, and adds that value to the byte
in the same position in the implied output register. The addition is
saturated to an unsigned byte in the same way as \c{PADDUSB}.

To work out the implied register, invert the lowest bit in the register
number. So \c{PDISTIB MM0,M64} would put the result in \c{MM1}, but
\c{PDISTIB MM1,M64} would put the result in \c{MM0}.

Note that \c{PDISTIB} cannot take a register as its second source
operand.

Operation:

\c    dstI[0-7]     := dstI[0-7]   + ABS(src0[0-7] - src1[0-7]),
\c    dstI[8-15]    := dstI[8-15]  + ABS(src0[8-15] - src1[8-15]),
\c    .......
\c    .......
\c    dstI[56-63]   := dstI[56-63] + ABS(src0[56-63] - src1[56-63]).


\S{insPEXTRW} \i\c{PEXTRW}: Extract Word

\c PEXTRW reg32,mm,imm8          ; 0F C5 /r ib     [KATMAI,MMX]
\c PEXTRW reg32,xmm,imm8         ; 66 0F C5 /r ib  [WILLAMETTE,SSE2]

\c{PEXTRW} moves the word in the source register (second operand)
that is pointed to by the count operand (third operand), into the
lower half of a 32-bit general purpose register. The upper half of
the register is cleared to all 0s.

When the source operand is an \c{MMX} register, the two least
significant bits of the count specify the source word. When it is
an \c{SSE} register, the three least significant bits specify the
word location.


\S{insPF2ID} \i\c{PF2ID}: Packed Single-Precision FP to Integer Convert

\c PF2ID mm1,mm2/m64             ; 0F 0F /r 1D          [PENT,3DNOW]

\c{PF2ID} converts two single-precision FP values in the source operand
to signed 32-bit integers, using truncation, and stores them in the
destination operand. Source values that are outside the range supported
by the destination are saturated to the largest absolute value of the
same sign.


\S{insPF2IW} \i\c{PF2IW}: Packed Single-Precision FP to Integer Word Convert

\c PF2IW mm1,mm2/m64             ; 0F 0F /r 1C          [PENT,3DNOW]

\c{PF2IW} converts two single-precision FP values in the source operand
to signed 16-bit integers, using truncation, and stores them in the
destination operand. Source values that are outside the range supported
by the destination are saturated to the largest absolute value of the
same sign.

\b In the K6-2 and K6-III, the 16-bit value is zero-extended to 32-bits
before storing.

\b In the K6-2+, K6-III+ and Athlon processors, the value is sign-extended
to 32-bits before storing.


\S{insPFACC} \i\c{PFACC}: Packed Single-Precision FP Accumulate

\c PFACC mm1,mm2/m64             ; 0F 0F /r AE          [PENT,3DNOW]

\c{PFACC} adds the two single-precision FP values from the destination
operand together, then adds the two single-precision FP values from the
source operand, and places the results in the low and high doublewords
of the destination operand.

The operation is:

\c    dst[0-31]   := dst[0-31] + dst[32-63],
\c    dst[32-63]  := src[0-31] + src[32-63].


\S{insPFADD} \i\c{PFADD}: Packed Single-Precision FP Addition

\c PFADD mm1,mm2/m64             ; 0F 0F /r 9E          [PENT,3DNOW]

\c{PFADD} performs addition on each of two packed single-precision
FP value pairs.

\c    dst[0-31]   := dst[0-31]  + src[0-31],
\c    dst[32-63]  := dst[32-63] + src[32-63].


\S{insPFCMP} \i\c{PFCMPxx}: Packed Single-Precision FP Compare
\I\c{PFCMPEQ} \I\c{PFCMPGE} \I\c{PFCMPGT}

\c PFCMPEQ mm1,mm2/m64           ; 0F 0F /r B0          [PENT,3DNOW]
\c PFCMPGE mm1,mm2/m64           ; 0F 0F /r 90          [PENT,3DNOW]
\c PFCMPGT mm1,mm2/m64           ; 0F 0F /r A0          [PENT,3DNOW]

The \c{PFCMPxx} instructions compare the packed single-point FP values
in the source and destination operands, and set the destination
according to the result. If the condition is true, the destination is
set to all 1s, otherwise it's set to all 0s.

\b \c{PFCMPEQ} tests whether dst == src;

\b \c{PFCMPGE} tests whether dst >= src;

\b \c{PFCMPGT} tests whether dst >  src.


\S{insPFMAX} \i\c{PFMAX}: Packed Single-Precision FP Maximum

\c PFMAX mm1,mm2/m64             ; 0F 0F /r A4          [PENT,3DNOW]

\c{PFMAX} returns the higher of each pair of single-precision FP values.
If the higher value is zero, it is returned as positive zero.


\S{insPFMIN} \i\c{PFMIN}: Packed Single-Precision FP Minimum

\c PFMIN mm1,mm2/m64             ; 0F 0F /r 94          [PENT,3DNOW]

\c{PFMIN} returns the lower of each pair of single-precision FP values.
If the lower value is zero, it is returned as positive zero.


\S{insPFMUL} \i\c{PFMUL}: Packed Single-Precision FP Multiply

\c PFMUL mm1,mm2/m64             ; 0F 0F /r B4          [PENT,3DNOW]

\c{PFMUL} returns the product of each pair of single-precision FP values.

\c    dst[0-31]  := dst[0-31]  * src[0-31],
\c    dst[32-63] := dst[32-63] * src[32-63].


\S{insPFNACC} \i\c{PFNACC}: Packed Single-Precision FP Negative Accumulate

\c PFNACC mm1,mm2/m64            ; 0F 0F /r 8A          [PENT,3DNOW]

\c{PFNACC} performs a negative accumulate of the two single-precision
FP values in the source and destination registers. The result of the
accumulate from the destination register is stored in the low doubleword
of the destination, and the result of the source accumulate is stored in
the high doubleword of the destination register.

The operation is:

\c    dst[0-31]  := dst[0-31] - dst[32-63],
\c    dst[32-63] := src[0-31] - src[32-63].


\S{insPFPNACC} \i\c{PFPNACC}: Packed Single-Precision FP Mixed Accumulate

\c PFPNACC mm1,mm2/m64           ; 0F 0F /r 8E          [PENT,3DNOW]

\c{PFPNACC} performs a positive accumulate of the two single-precision
FP values in the source register and a negative accumulate of the
destination register. The result of the accumulate from the destination
register is stored in the low doubleword of the destination, and the
result of the source accumulate is stored in the high doubleword of the
destination register.

The operation is:

\c    dst[0-31]  := dst[0-31] - dst[32-63],
\c    dst[32-63] := src[0-31] + src[32-63].


\S{insPFRCP} \i\c{PFRCP}: Packed Single-Precision FP Reciprocal Approximation

\c PFRCP mm1,mm2/m64             ; 0F 0F /r 96          [PENT,3DNOW]

\c{PFRCP} performs a low precision estimate of the reciprocal of the
low-order single-precision FP value in the source operand, storing the
result in both halves of the destination register. The result is accurate
to 14 bits.

For higher precision reciprocals, this instruction should be followed by
two more instructions: \c{PFRCPIT1} (\k{insPFRCPIT1}) and \c{PFRCPIT2}
(\k{insPFRCPIT1}). This will result in a 24-bit accuracy. For more details,
see the AMD 3DNow! technology manual.


\S{insPFRCPIT1} \i\c{PFRCPIT1}: Packed Single-Precision FP Reciprocal,
First Iteration Step

\c PFRCPIT1 mm1,mm2/m64          ; 0F 0F /r A6          [PENT,3DNOW]

\c{PFRCPIT1} performs the first intermediate step in the calculation of
the reciprocal of a single-precision FP value. The first source value
(\c{mm1} is the original value, and the second source value (\c{mm2/m64}
is the result of a \c{PFRCP} instruction.

For the final step in a reciprocal, returning the full 24-bit accuracy
of a single-precision FP value, see \c{PFRCPIT2} (\k{insPFRCPIT2}). For
more details, see the AMD 3DNow! technology manual.


\S{insPFRCPIT2} \i\c{PFRCPIT2}: Packed Single-Precision FP
Reciprocal/ Reciprocal Square Root, Second Iteration Step

\c PFRCPIT2 mm1,mm2/m64          ; 0F 0F /r B6          [PENT,3DNOW]

\c{PFRCPIT2} performs the second and final intermediate step in the
calculation of a reciprocal or reciprocal square root, refining the
values returned by the \c{PFRCP} and \c{PFRSQRT} instructions,
respectively.

The first source value (\c{mm1}) is the output of either a \c{PFRCPIT1}
or a \c{PFRSQIT1} instruction, and the second source is the output of
either the \c{PFRCP} or the \c{PFRSQRT} instruction. For more details,
see the AMD 3DNow! technology manual.


\S{insPFRSQIT1} \i\c{PFRSQIT1}: Packed Single-Precision FP Reciprocal
Square Root, First Iteration Step

\c PFRSQIT1 mm1,mm2/m64          ; 0F 0F /r A7          [PENT,3DNOW]

\c{PFRSQIT1} performs the first intermediate step in the calculation of
the reciprocal square root of a single-precision FP value. The first
source value (\c{mm1} is the square of the result of a \c{PFRSQRT}
instruction, and the second source value (\c{mm2/m64} is the original
value.

For the final step in a calculation, returning the full 24-bit accuracy
of a single-precision FP value, see \c{PFRCPIT2} (\k{insPFRCPIT2}). For
more details, see the AMD 3DNow! technology manual.


\S{insPFRSQRT} \i\c{PFRSQRT}: Packed Single-Precision FP Reciprocal
Square Root Approximation

\c PFRSQRT mm1,mm2/m64           ; 0F 0F /r 97          [PENT,3DNOW]

\c{PFRSQRT} performs a low precision estimate of the reciprocal square
root of the low-order single-precision FP value in the source operand,
storing the result in both halves of the destination register. The result
is accurate to 15 bits.

For higher precision reciprocals, this instruction should be followed by
two more instructions: \c{PFRSQIT1} (\k{insPFRSQIT1}) and \c{PFRCPIT2}
(\k{insPFRCPIT1}). This will result in a 24-bit accuracy. For more details,
see the AMD 3DNow! technology manual.


\S{insPFSUB} \i\c{PFSUB}: Packed Single-Precision FP Subtract

\c PFSUB mm1,mm2/m64             ; 0F 0F /r 9A          [PENT,3DNOW]

\c{PFSUB} subtracts the single-precision FP values in the source from
those in the destination, and stores the result in the destination
operand.

\c    dst[0-31]  := dst[0-31]  - src[0-31],
\c    dst[32-63] := dst[32-63] - src[32-63].


\S{insPFSUBR} \i\c{PFSUBR}: Packed Single-Precision FP Reverse Subtract

\c PFSUBR mm1,mm2/m64            ; 0F 0F /r AA          [PENT,3DNOW]

\c{PFSUBR} subtracts the single-precision FP values in the destination
from those in the source, and stores the result in the destination
operand.

\c    dst[0-31]  := src[0-31]  - dst[0-31],
\c    dst[32-63] := src[32-63] - dst[32-63].


\S{insPI2FD} \i\c{PI2FD}: Packed Doubleword Integer to Single-Precision FP Convert

\c PI2FD mm1,mm2/m64             ; 0F 0F /r 0D          [PENT,3DNOW]

\c{PF2ID} converts two signed 32-bit integers in the source operand
to single-precision FP values, using truncation of significant digits,
and stores them in the destination operand.


\S{insPF2IW} \i\c{PF2IW}: Packed Word Integer to Single-Precision FP Convert

\c PI2FW mm1,mm2/m64             ; 0F 0F /r 0C          [PENT,3DNOW]

\c{PF2IW} converts two signed 16-bit integers in the source operand
to single-precision FP values, and stores them in the destination
operand. The input values are in the low word of each doubleword.


\S{insPINSRW} \i\c{PINSRW}: Insert Word

\c PINSRW mm,r16/r32/m16,imm8    ;0F C4 /r ib      [KATMAI,MMX]
\c PINSRW xmm,r16/r32/m16,imm8   ;66 0F C4 /r ib   [WILLAMETTE,SSE2]

\c{PINSRW} loads a word from a 16-bit register (or the low half of a
32-bit register), or from memory, and loads it to the word position
in the destination register, pointed at by the count operand (third
operand). If the destination is an \c{MMX} register, the low two bits
of the count byte are used, if it is an \c{XMM} register the low 3
bits are used. The insertion is done in such a way that the other
words from the destination register are left untouched.


\S{insPMACHRIW} \i\c{PMACHRIW}: Packed Multiply and Accumulate with Rounding

\c PMACHRIW mm,m64               ; 0F 5E /r             [CYRIX,MMX]

\c{PMACHRIW} takes two packed 16-bit integer inputs, multiplies the
values in the inputs, rounds on bit 15 of each result, then adds bits
15-30 of each result to the corresponding position of the \e{implied}
destination register.

The operation of this instruction is:

\c    dstI[0-15]  := dstI[0-15]  + (mm[0-15] *m64[0-15]
\c                                           + 0x00004000)[15-30],
\c    dstI[16-31] := dstI[16-31] + (mm[16-31]*m64[16-31]
\c                                           + 0x00004000)[15-30],
\c    dstI[32-47] := dstI[32-47] + (mm[32-47]*m64[32-47]
\c                                           + 0x00004000)[15-30],
\c    dstI[48-63] := dstI[48-63] + (mm[48-63]*m64[48-63]
\c                                           + 0x00004000)[15-30].

Note that \c{PMACHRIW} cannot take a register as its second source
operand.


\S{insPMADDWD} \i\c{PMADDWD}: MMX Packed Multiply and Add

\c PMADDWD mm1,mm2/m64           ; 0F F5 /r             [PENT,MMX]
\c PMADDWD xmm1,xmm2/m128        ; 66 0F F5 /r     [WILLAMETTE,SSE2]

\c{PMADDWD} treats its two inputs as vectors of signed words. It
multiplies corresponding elements of the two operands, giving doubleword
results. These are then added together in pairs and stored in the
destination operand.

The operation of this instruction is:

\c    dst[0-31]   := (dst[0-15] * src[0-15])
\c                                + (dst[16-31] * src[16-31]);
\c    dst[32-63]  := (dst[32-47] * src[32-47])
\c                                + (dst[48-63] * src[48-63]);

The following apply to the \c{SSE} version of the instruction:

\c    dst[64-95]  := (dst[64-79] * src[64-79])
\c                                + (dst[80-95] * src[80-95]);
\c    dst[96-127] := (dst[96-111] * src[96-111])
\c                                + (dst[112-127] * src[112-127]).


\S{insPMAGW} \i\c{PMAGW}: MMX Packed Magnitude

\c PMAGW mm1,mm2/m64             ; 0F 52 /r             [CYRIX,MMX]

\c{PMAGW}, specific to the Cyrix MMX extensions, treats both its
operands as vectors of four signed words. It compares the absolute
values of the words in corresponding positions, and sets each word
of the destination (first) operand to whichever of the two words in
that position had the larger absolute value.


\S{insPMAXSW} \i\c{PMAXSW}: Packed Signed Integer Word Maximum

\c PMAXSW mm1,mm2/m64            ; 0F EE /r        [KATMAI,MMX]
\c PMAXSW xmm1,xmm2/m128         ; 66 0F EE /r     [WILLAMETTE,SSE2]

\c{PMAXSW} compares each pair of words in the two source operands, and
for each pair it stores the maximum value in the destination register.


\S{insPMAXUB} \i\c{PMAXUB}: Packed Unsigned Integer Byte Maximum

\c PMAXUB mm1,mm2/m64            ; 0F DE /r        [KATMAI,MMX]
\c PMAXUB xmm1,xmm2/m128         ; 66 0F DE /r     [WILLAMETTE,SSE2]

\c{PMAXUB} compares each pair of bytes in the two source operands, and
for each pair it stores the maximum value in the destination register.


\S{insPMINSW} \i\c{PMINSW}: Packed Signed Integer Word Minimum

\c PMINSW mm1,mm2/m64            ; 0F EA /r        [KATMAI,MMX]
\c PMINSW xmm1,xmm2/m128         ; 66 0F EA /r     [WILLAMETTE,SSE2]

\c{PMINSW} compares each pair of words in the two source operands, and
for each pair it stores the minimum value in the destination register.


\S{insPMINUB} \i\c{PMINUB}: Packed Unsigned Integer Byte Minimum

\c PMINUB mm1,mm2/m64            ; 0F DA /r        [KATMAI,MMX]
\c PMINUB xmm1,xmm2/m128         ; 66 0F DA /r     [WILLAMETTE,SSE2]

\c{PMINUB} compares each pair of bytes in the two source operands, and
for each pair it stores the minimum value in the destination register.


\S{insPMOVMSKB} \i\c{PMOVMSKB}: Move Byte Mask To Integer

\c PMOVMSKB reg32,mm             ; 0F D7 /r        [KATMAI,MMX]
\c PMOVMSKB reg32,xmm            ; 66 0F D7 /r     [WILLAMETTE,SSE2]

\c{PMOVMSKB} returns an 8-bit or 16-bit mask formed of the most
significant bits of each byte of source operand (8-bits for an
\c{MMX} register, 16-bits for an \c{XMM} register).


\S{insPMULHRW} \i\c{PMULHRWC}, \i\c{PMULHRIW}: Multiply Packed 16-bit Integers
With Rounding, and Store High Word

\c PMULHRWC mm1,mm2/m64         ; 0F 59 /r              [CYRIX,MMX]
\c PMULHRIW mm1,mm2/m64         ; 0F 5D /r              [CYRIX,MMX]

These instructions take two packed 16-bit integer inputs, multiply the
values in the inputs, round on bit 15 of each result, then store bits
15-30 of each result to the corresponding position of the destination
register.

\b For \c{PMULHRWC}, the destination is the first source operand.

\b For \c{PMULHRIW}, the destination is an implied register (worked out
as described for \c{PADDSIW} (\k{insPADDSIW})).

The operation of this instruction is:

\c    dst[0-15]  := (src1[0-15] *src2[0-15]  + 0x00004000)[15-30]
\c    dst[16-31] := (src1[16-31]*src2[16-31] + 0x00004000)[15-30]
\c    dst[32-47] := (src1[32-47]*src2[32-47] + 0x00004000)[15-30]
\c    dst[48-63] := (src1[48-63]*src2[48-63] + 0x00004000)[15-30]

See also \c{PMULHRWA} (\k{insPMULHRWA}) for a 3DNow! version of this
instruction.


\S{insPMULHRWA} \i\c{PMULHRWA}: Multiply Packed 16-bit Integers
With Rounding, and Store High Word

\c PMULHRWA mm1,mm2/m64          ; 0F 0F /r B7     [PENT,3DNOW]

\c{PMULHRWA} takes two packed 16-bit integer inputs, multiplies
the values in the inputs, rounds on bit 16 of each result, then
stores bits 16-31 of each result to the corresponding position
of the destination register.

The operation of this instruction is:

\c    dst[0-15]  := (src1[0-15] *src2[0-15]  + 0x00008000)[16-31];
\c    dst[16-31] := (src1[16-31]*src2[16-31] + 0x00008000)[16-31];
\c    dst[32-47] := (src1[32-47]*src2[32-47] + 0x00008000)[16-31];
\c    dst[48-63] := (src1[48-63]*src2[48-63] + 0x00008000)[16-31].

See also \c{PMULHRWC} (\k{insPMULHRW}) for a Cyrix version of this
instruction.


\S{insPMULHUW} \i\c{PMULHUW}: Multiply Packed 16-bit Integers,
and Store High Word

\c PMULHUW mm1,mm2/m64           ; 0F E4 /r        [KATMAI,MMX]
\c PMULHUW xmm1,xmm2/m128        ; 66 0F E4 /r     [WILLAMETTE,SSE2]

\c{PMULHUW} takes two packed unsigned 16-bit integer inputs, multiplies
the values in the inputs, then stores bits 16-31 of each result to the
corresponding position of the destination register.


\S{insPMULHW} \i\c{PMULHW}, \i\c{PMULLW}: Multiply Packed 16-bit Integers,
and Store

\c PMULHW mm1,mm2/m64            ; 0F E5 /r             [PENT,MMX]
\c PMULLW mm1,mm2/m64            ; 0F D5 /r             [PENT,MMX]

\c PMULHW xmm1,xmm2/m128         ; 66 0F E5 /r     [WILLAMETTE,SSE2]
\c PMULLW xmm1,xmm2/m128         ; 66 0F D5 /r     [WILLAMETTE,SSE2]

\c{PMULxW} takes two packed unsigned 16-bit integer inputs, and
multiplies the values in the inputs, forming doubleword results.

\b \c{PMULHW} then stores the top 16 bits of each doubleword in the
destination (first) operand;

\b \c{PMULLW} stores the bottom 16 bits of each doubleword in the
destination operand.


\S{insPMULUDQ} \i\c{PMULUDQ}: Multiply Packed Unsigned
32-bit Integers, and Store.

\c PMULUDQ mm1,mm2/m64           ; 0F F4 /r        [WILLAMETTE,SSE2]
\c PMULUDQ xmm1,xmm2/m128        ; 66 0F F4 /r     [WILLAMETTE,SSE2]

\c{PMULUDQ} takes two packed unsigned 32-bit integer inputs, and
multiplies the values in the inputs, forming quadword results. The
source is either an unsigned doubleword in the low doubleword of a
64-bit operand, or it's two unsigned doublewords in the first and
third doublewords of a 128-bit operand. This produces either one or
two 64-bit results, which are stored in the respective quadword
locations of the destination register.

The operation is:

\c    dst[0-63]   := dst[0-31]  * src[0-31];
\c    dst[64-127] := dst[64-95] * src[64-95].


\S{insPMVccZB} \i\c{PMVccZB}: MMX Packed Conditional Move

\c PMVZB mmxreg,mem64            ; 0F 58 /r             [CYRIX,MMX]
\c PMVNZB mmxreg,mem64           ; 0F 5A /r             [CYRIX,MMX]
\c PMVLZB mmxreg,mem64           ; 0F 5B /r             [CYRIX,MMX]
\c PMVGEZB mmxreg,mem64          ; 0F 5C /r             [CYRIX,MMX]

These instructions, specific to the Cyrix MMX extensions, perform
parallel conditional moves. The two input operands are treated as
vectors of eight bytes. Each byte of the destination (first) operand
is either written from the corresponding byte of the source (second)
operand, or left alone, depending on the value of the byte in the
\e{implied} operand (specified in the same way as \c{PADDSIW}, in
\k{insPADDSIW}).

\b \c{PMVZB} performs each move if the corresponding byte in the
implied operand is zero;

\b \c{PMVNZB} moves if the byte is non-zero;

\b \c{PMVLZB} moves if the byte is less than zero;

\b \c{PMVGEZB} moves if the byte is greater than or equal to zero.

Note that these instructions cannot take a register as their second
source operand.


\S{insPOP} \i\c{POP}: Pop Data from Stack

\c POP reg16                     ; o16 58+r             [8086]
\c POP reg32                     ; o32 58+r             [386]

\c POP r/m16                     ; o16 8F /0            [8086]
\c POP r/m32                     ; o32 8F /0            [386]

\c POP CS                        ; 0F                   [8086,UNDOC]
\c POP DS                        ; 1F                   [8086]
\c POP ES                        ; 07                   [8086]
\c POP SS                        ; 17                   [8086]
\c POP FS                        ; 0F A1                [386]
\c POP GS                        ; 0F A9                [386]

\c{POP} loads a value from the stack (from \c{[SS:SP]} or
\c{[SS:ESP]}) and then increments the stack pointer.

The address-size attribute of the instruction determines whether
\c{SP} or \c{ESP} is used as the stack pointer: to deliberately
override the default given by the \c{BITS} setting, you can use an
\i\c{a16} or \i\c{a32} prefix.

The operand-size attribute of the instruction determines whether the
stack pointer is incremented by 2 or 4: this means that segment
register pops in \c{BITS 32} mode will pop 4 bytes off the stack and
discard the upper two of them. If you need to override that, you can
use an \i\c{o16} or \i\c{o32} prefix.

The above opcode listings give two forms for general-purpose
register pop instructions: for example, \c{POP BX} has the two forms
\c{5B} and \c{8F C3}. NASM will always generate the shorter form
when given \c{POP BX}. NDISASM will disassemble both.

\c{POP CS} is not a documented instruction, and is not supported on
any processor above the 8086 (since they use \c{0Fh} as an opcode
prefix for instruction set extensions). However, at least some 8086
processors do support it, and so NASM generates it for completeness.


\S{insPOPA} \i\c{POPAx}: Pop All General-Purpose Registers

\c POPA                          ; 61                   [186]
\c POPAW                         ; o16 61               [186]
\c POPAD                         ; o32 61               [386]

\b \c{POPAW} pops a word from the stack into each of, successively,
\c{DI}, \c{SI}, \c{BP}, nothing (it discards a word from the stack
which was a placeholder for \c{SP}), \c{BX}, \c{DX}, \c{CX} and
\c{AX}. It is intended to reverse the operation of \c{PUSHAW} (see
\k{insPUSHA}), but it ignores the value for \c{SP} that was pushed
on the stack by \c{PUSHAW}.

\b \c{POPAD} pops twice as much data, and places the results in
\c{EDI}, \c{ESI}, \c{EBP}, nothing (placeholder for \c{ESP}),
\c{EBX}, \c{EDX}, \c{ECX} and \c{EAX}. It reverses the operation of
\c{PUSHAD}.

\c{POPA} is an alias mnemonic for either \c{POPAW} or \c{POPAD},
depending on the current \c{BITS} setting.

Note that the registers are popped in reverse order of their numeric
values in opcodes (see \k{iref-rv}).


\S{insPOPF} \i\c{POPFx}: Pop Flags Register

\c POPF                          ; 9D                   [8086]
\c POPFW                         ; o16 9D               [8086]
\c POPFD                         ; o32 9D               [386]

\b \c{POPFW} pops a word from the stack and stores it in the bottom 16
bits of the flags register (or the whole flags register, on
processors below a 386).

\b \c{POPFD} pops a doubleword and stores it in the entire flags register.

\c{POPF} is an alias mnemonic for either \c{POPFW} or \c{POPFD},
depending on the current \c{BITS} setting.

See also \c{PUSHF} (\k{insPUSHF}).


\S{insPOR} \i\c{POR}: MMX Bitwise OR

\c POR mm1,mm2/m64               ; 0F EB /r             [PENT,MMX]
\c POR xmm1,xmm2/m128            ; 66 0F EB /r     [WILLAMETTE,SSE2]

\c{POR} performs a bitwise OR operation between its two operands
(i.e. each bit of the result is 1 if and only if at least one of the
corresponding bits of the two inputs was 1), and stores the result
in the destination (first) operand.


\S{insPREFETCH} \i\c{PREFETCH}: Prefetch Data Into Caches

\c PREFETCH mem8                 ; 0F 0D /0             [PENT,3DNOW]
\c PREFETCHW mem8                ; 0F 0D /1             [PENT,3DNOW]

\c{PREFETCH} and \c{PREFETCHW} fetch the line of data from memory that
contains the specified byte. \c{PREFETCHW} performs differently on the
Athlon to earlier processors.

For more details, see the 3DNow! Technology Manual.


\S{insPREFETCHh} \i\c{PREFETCHh}: Prefetch Data Into Caches
\I\c{PREFETCHNTA} \I\c{PREFETCHT0} \I\c{PREFETCHT1} \I\c{PREFETCHT2}

\c PREFETCHNTA m8                ; 0F 18 /0        [KATMAI]
\c PREFETCHT0 m8                 ; 0F 18 /1        [KATMAI]
\c PREFETCHT1 m8                 ; 0F 18 /2        [KATMAI]
\c PREFETCHT2 m8                 ; 0F 18 /3        [KATMAI]

The \c{PREFETCHh} instructions fetch the line of data from memory
that contains the specified byte. It is placed in the cache
according to rules specified by locality hints \c{h}:

The hints are:

\b \c{T0} (temporal data) - prefetch data into all levels of the
cache hierarchy.

\b \c{T1} (temporal data with respect to first level cache) -
prefetch data into level 2 cache and higher.

\b \c{T2} (temporal data with respect to second level cache) -
prefetch data into level 2 cache and higher.

\b \c{NTA} (non-temporal data with respect to all cache levels) -
prefetch data into non-temporal cache structure and into a
location close to the processor, minimizing cache pollution.

Note that this group of instructions doesn't provide a guarantee
that the data will be in the cache when it is needed. For more
details, see the Intel IA32 Software Developer Manual, Volume 2.


\S{insPSADBW} \i\c{PSADBW}: Packed Sum of Absolute Differences

\c PSADBW mm1,mm2/m64            ; 0F F6 /r        [KATMAI,MMX]
\c PSADBW xmm1,xmm2/m128         ; 66 0F F6 /r     [WILLAMETTE,SSE2]

\c{PSADBW} The PSADBW instruction computes the absolute value of the
difference of the packed unsigned bytes in the two source operands.
These differences are then summed to produce a word result in the lower
16-bit field of the destination register; the rest of the register is
cleared. The destination operand is an \c{MMX} or an \c{XMM} register.
The source operand can either be a register or a memory operand.


\S{insPSHUFD} \i\c{PSHUFD}: Shuffle Packed Doublewords

\c PSHUFD xmm1,xmm2/m128,imm8    ; 66 0F 70 /r ib  [WILLAMETTE,SSE2]

\c{PSHUFD} shuffles the doublewords in the source (second) operand
according to the encoding specified by imm8, and stores the result
in the destination (first) operand.

Bits 0 and 1 of imm8 encode the source position of the doubleword to
be copied to position 0 in the destination operand. Bits 2 and 3
encode for position 1, bits 4 and 5 encode for position 2, and bits
6 and 7 encode for position 3. For example, an encoding of 10 in
bits 0 and 1 of imm8 indicates that the doubleword at bits 64-95 of
the source operand will be copied to bits 0-31 of the destination.


\S{insPSHUFHW} \i\c{PSHUFHW}: Shuffle Packed High Words

\c PSHUFHW xmm1,xmm2/m128,imm8   ; F3 0F 70 /r ib  [WILLAMETTE,SSE2]

\c{PSHUFW} shuffles the words in the high quadword of the source
(second) operand according to the encoding specified by imm8, and
stores the result in the high quadword of the destination (first)
operand.

The operation of this instruction is similar to the \c{PSHUFW}
instruction, except that the source and destination are the top
quadword of a 128-bit operand, instead of being 64-bit operands.
The low quadword is copied from the source to the destination
without any changes.


\S{insPSHUFLW} \i\c{PSHUFLW}: Shuffle Packed Low Words

\c PSHUFLW xmm1,xmm2/m128,imm8   ; F2 0F 70 /r ib  [WILLAMETTE,SSE2]

\c{PSHUFLW} shuffles the words in the low quadword of the source
(second) operand according to the encoding specified by imm8, and
stores the result in the low quadword of the destination (first)
operand.

The operation of this instruction is similar to the \c{PSHUFW}
instruction, except that the source and destination are the low
quadword of a 128-bit operand, instead of being 64-bit operands.
The high quadword is copied from the source to the destination
without any changes.


\S{insPSHUFW} \i\c{PSHUFW}: Shuffle Packed Words

\c PSHUFW mm1,mm2/m64,imm8       ; 0F 70 /r ib     [KATMAI,MMX]

\c{PSHUFW} shuffles the words in the source (second) operand
according to the encoding specified by imm8, and stores the result
in the destination (first) operand.

Bits 0 and 1 of imm8 encode the source position of the word to be
copied to position 0 in the destination operand. Bits 2 and 3 encode
for position 1, bits 4 and 5 encode for position 2, and bits 6 and 7
encode for position 3. For example, an encoding of 10 in bits 0 and 1
of imm8 indicates that the word at bits 32-47 of the source operand
will be copied to bits 0-15 of the destination.


\S{insPSLLD} \i\c{PSLLx}: Packed Data Bit Shift Left Logical

\c PSLLW mm1,mm2/m64             ; 0F F1 /r             [PENT,MMX]
\c PSLLW mm,imm8                 ; 0F 71 /6 ib          [PENT,MMX]

\c PSLLW xmm1,xmm2/m128          ; 66 0F F1 /r     [WILLAMETTE,SSE2]
\c PSLLW xmm,imm8                ; 66 0F 71 /6 ib  [WILLAMETTE,SSE2]

\c PSLLD mm1,mm2/m64             ; 0F F2 /r             [PENT,MMX]
\c PSLLD mm,imm8                 ; 0F 72 /6 ib          [PENT,MMX]

\c PSLLD xmm1,xmm2/m128          ; 66 0F F2 /r     [WILLAMETTE,SSE2]
\c PSLLD xmm,imm8                ; 66 0F 72 /6 ib  [WILLAMETTE,SSE2]

\c PSLLQ mm1,mm2/m64             ; 0F F3 /r             [PENT,MMX]
\c PSLLQ mm,imm8                 ; 0F 73 /6 ib          [PENT,MMX]

\c PSLLQ xmm1,xmm2/m128          ; 66 0F F3 /r     [WILLAMETTE,SSE2]
\c PSLLQ xmm,imm8                ; 66 0F 73 /6 ib  [WILLAMETTE,SSE2]

\c PSLLDQ xmm1,imm8              ; 66 0F 73 /7 ib  [WILLAMETTE,SSE2]

\c{PSLLx} performs logical left shifts of the data elements in the
destination (first) operand, moving each bit in the separate elements
left by the number of bits specified in the source (second) operand,
clearing the low-order bits as they are vacated. \c{PSLLDQ} 
shifts bytes, not bits.

\b \c{PSLLW} shifts word sized elements.

\b \c{PSLLD} shifts doubleword sized elements.

\b \c{PSLLQ} shifts quadword sized elements.

\b \c{PSLLDQ} shifts double quadword sized elements.


\S{insPSRAD} \i\c{PSRAx}: Packed Data Bit Shift Right Arithmetic

\c PSRAW mm1,mm2/m64             ; 0F E1 /r             [PENT,MMX]
\c PSRAW mm,imm8                 ; 0F 71 /4 ib          [PENT,MMX]

\c PSRAW xmm1,xmm2/m128          ; 66 0F E1 /r     [WILLAMETTE,SSE2]
\c PSRAW xmm,imm8                ; 66 0F 71 /4 ib  [WILLAMETTE,SSE2]

\c PSRAD mm1,mm2/m64             ; 0F E2 /r             [PENT,MMX]
\c PSRAD mm,imm8                 ; 0F 72 /4 ib          [PENT,MMX]

\c PSRAD xmm1,xmm2/m128          ; 66 0F E2 /r     [WILLAMETTE,SSE2]
\c PSRAD xmm,imm8                ; 66 0F 72 /4 ib  [WILLAMETTE,SSE2]

\c{PSRAx} performs arithmetic right shifts of the data elements in the
destination (first) operand, moving each bit in the separate elements
right by the number of bits specified in the source (second) operand,
setting the high-order bits to the value of the original sign bit.

\b \c{PSRAW} shifts word sized elements.

\b \c{PSRAD} shifts doubleword sized elements.


\S{insPSRLD} \i\c{PSRLx}: Packed Data Bit Shift Right Logical

\c PSRLW mm1,mm2/m64             ; 0F D1 /r             [PENT,MMX]
\c PSRLW mm,imm8                 ; 0F 71 /2 ib          [PENT,MMX]

\c PSRLW xmm1,xmm2/m128          ; 66 0F D1 /r     [WILLAMETTE,SSE2]
\c PSRLW xmm,imm8                ; 66 0F 71 /2 ib  [WILLAMETTE,SSE2]

\c PSRLD mm1,mm2/m64             ; 0F D2 /r             [PENT,MMX]
\c PSRLD mm,imm8                 ; 0F 72 /2 ib          [PENT,MMX]

\c PSRLD xmm1,xmm2/m128          ; 66 0F D2 /r     [WILLAMETTE,SSE2]
\c PSRLD xmm,imm8                ; 66 0F 72 /2 ib  [WILLAMETTE,SSE2]

\c PSRLQ mm1,mm2/m64             ; 0F D3 /r             [PENT,MMX]
\c PSRLQ mm,imm8                 ; 0F 73 /2 ib          [PENT,MMX]

\c PSRLQ xmm1,xmm2/m128          ; 66 0F D3 /r     [WILLAMETTE,SSE2]
\c PSRLQ xmm,imm8                ; 66 0F 73 /2 ib  [WILLAMETTE,SSE2]

\c PSRLDQ xmm1,imm8              ; 66 0F 73 /3 ib  [WILLAMETTE,SSE2]

\c{PSRLx} performs logical right shifts of the data elements in the
destination (first) operand, moving each bit in the separate elements
right by the number of bits specified in the source (second) operand,
clearing the high-order bits as they are vacated. \c{PSRLDQ} 
shifts bytes, not bits.

\b \c{PSRLW} shifts word sized elements.

\b \c{PSRLD} shifts doubleword sized elements.

\b \c{PSRLQ} shifts quadword sized elements.

\b \c{PSRLDQ} shifts double quadword sized elements.


\S{insPSUBB} \i\c{PSUBx}: Subtract Packed Integers

\c PSUBB mm1,mm2/m64             ; 0F F8 /r             [PENT,MMX]
\c PSUBW mm1,mm2/m64             ; 0F F9 /r             [PENT,MMX]
\c PSUBD mm1,mm2/m64             ; 0F FA /r             [PENT,MMX]
\c PSUBQ mm1,mm2/m64             ; 0F FB /r        [WILLAMETTE,SSE2]

\c PSUBB xmm1,xmm2/m128          ; 66 0F F8 /r     [WILLAMETTE,SSE2]
\c PSUBW xmm1,xmm2/m128          ; 66 0F F9 /r     [WILLAMETTE,SSE2]
\c PSUBD xmm1,xmm2/m128          ; 66 0F FA /r     [WILLAMETTE,SSE2]
\c PSUBQ xmm1,xmm2/m128          ; 66 0F FB /r     [WILLAMETTE,SSE2]

\c{PSUBx} subtracts packed integers in the source operand from those
in the destination operand. It doesn't differentiate between signed
and unsigned integers, and doesn't set any of the flags.

\b \c{PSUBB} operates on byte sized elements.

\b \c{PSUBW} operates on word sized elements.

\b \c{PSUBD} operates on doubleword sized elements.

\b \c{PSUBQ} operates on quadword sized elements.


\S{insPSUBSB} \i\c{PSUBSxx}, \i\c{PSUBUSx}: Subtract Packed Integers With Saturation

\c PSUBSB mm1,mm2/m64            ; 0F E8 /r             [PENT,MMX]
\c PSUBSW mm1,mm2/m64            ; 0F E9 /r             [PENT,MMX]

\c PSUBSB xmm1,xmm2/m128         ; 66 0F E8 /r     [WILLAMETTE,SSE2]
\c PSUBSW xmm1,xmm2/m128         ; 66 0F E9 /r     [WILLAMETTE,SSE2]

\c PSUBUSB mm1,mm2/m64           ; 0F D8 /r             [PENT,MMX]
\c PSUBUSW mm1,mm2/m64           ; 0F D9 /r             [PENT,MMX]

\c PSUBUSB xmm1,xmm2/m128        ; 66 0F D8 /r     [WILLAMETTE,SSE2]
\c PSUBUSW xmm1,xmm2/m128        ; 66 0F D9 /r     [WILLAMETTE,SSE2]

\c{PSUBSx} and \c{PSUBUSx} subtracts packed integers in the source
operand from those in the destination operand, and use saturation for
results that are outside the range supported by the destination operand.

\b \c{PSUBSB} operates on signed bytes, and uses signed saturation on the
results.

\b \c{PSUBSW} operates on signed words, and uses signed saturation on the
results.

\b \c{PSUBUSB} operates on unsigned bytes, and uses signed saturation on
the results.

\b \c{PSUBUSW} operates on unsigned words, and uses signed saturation on
the results.


\S{insPSUBSIW} \i\c{PSUBSIW}: MMX Packed Subtract with Saturation to
Implied Destination

\c PSUBSIW mm1,mm2/m64           ; 0F 55 /r             [CYRIX,MMX]

\c{PSUBSIW}, specific to the Cyrix extensions to the MMX instruction
set, performs the same function as \c{PSUBSW}, except that the
result is not placed in the register specified by the first operand,
but instead in the implied destination register, specified as for
\c{PADDSIW} (\k{insPADDSIW}).


\S{insPSWAPD} \i\c{PSWAPD}: Swap Packed Data
\I\c{PSWAPW}

\c PSWAPD mm1,mm2/m64            ; 0F 0F /r BB     [PENT,3DNOW]

\c{PSWAPD} swaps the packed doublewords in the source operand, and
stores the result in the destination operand.

In the \c{K6-2} and \c{K6-III} processors, this opcode uses the
mnemonic \c{PSWAPW}, and it swaps the order of words when copying
from the source to the destination.

The operation in the \c{K6-2} and \c{K6-III} processors is

\c    dst[0-15]  = src[48-63];
\c    dst[16-31] = src[32-47];
\c    dst[32-47] = src[16-31];
\c    dst[48-63] = src[0-15].

The operation in the \c{K6-x+}, \c{ATHLON} and later processors is:

\c    dst[0-31]  = src[32-63];
\c    dst[32-63] = src[0-31].


\S{insPUNPCKHBW} \i\c{PUNPCKxxx}: Unpack and Interleave Data

\c PUNPCKHBW mm1,mm2/m64         ; 0F 68 /r             [PENT,MMX]
\c PUNPCKHWD mm1,mm2/m64         ; 0F 69 /r             [PENT,MMX]
\c PUNPCKHDQ mm1,mm2/m64         ; 0F 6A /r             [PENT,MMX]

\c PUNPCKHBW xmm1,xmm2/m128      ; 66 0F 68 /r     [WILLAMETTE,SSE2]
\c PUNPCKHWD xmm1,xmm2/m128      ; 66 0F 69 /r     [WILLAMETTE,SSE2]
\c PUNPCKHDQ xmm1,xmm2/m128      ; 66 0F 6A /r     [WILLAMETTE,SSE2]
\c PUNPCKHQDQ xmm1,xmm2/m128     ; 66 0F 6D /r     [WILLAMETTE,SSE2]

\c PUNPCKLBW mm1,mm2/m32         ; 0F 60 /r             [PENT,MMX]
\c PUNPCKLWD mm1,mm2/m32         ; 0F 61 /r             [PENT,MMX]
\c PUNPCKLDQ mm1,mm2/m32         ; 0F 62 /r             [PENT,MMX]

\c PUNPCKLBW xmm1,xmm2/m128      ; 66 0F 60 /r     [WILLAMETTE,SSE2]
\c PUNPCKLWD xmm1,xmm2/m128      ; 66 0F 61 /r     [WILLAMETTE,SSE2]
\c PUNPCKLDQ xmm1,xmm2/m128      ; 66 0F 62 /r     [WILLAMETTE,SSE2]
\c PUNPCKLQDQ xmm1,xmm2/m128     ; 66 0F 6C /r     [WILLAMETTE,SSE2]

\c{PUNPCKxx} all treat their operands as vectors, and produce a new
vector generated by interleaving elements from the two inputs. The
\c{PUNPCKHxx} instructions start by throwing away the bottom half of
each input operand, and the \c{PUNPCKLxx} instructions throw away
the top half.

The remaining elements, are then interleaved into the destination,
alternating elements from the second (source) operand and the first
(destination) operand: so the leftmost part of each element in the
result always comes from the second operand, and the rightmost from
the destination.

\b \c{PUNPCKxBW} works a byte at a time, producing word sized output
elements.

\b \c{PUNPCKxWD} works a word at a time, producing doubleword sized
output elements.

\b \c{PUNPCKxDQ} works a doubleword at a time, producing quadword sized
output elements.

\b \c{PUNPCKxQDQ} works a quadword at a time, producing double quadword
sized output elements.

So, for example, for \c{MMX} operands, if the first operand held
\c{0x7A6A5A4A3A2A1A0A} and the second held \c{0x7B6B5B4B3B2B1B0B},
then:

\b \c{PUNPCKHBW} would return \c{0x7B7A6B6A5B5A4B4A}.

\b \c{PUNPCKHWD} would return \c{0x7B6B7A6A5B4B5A4A}.

\b \c{PUNPCKHDQ} would return \c{0x7B6B5B4B7A6A5A4A}.

\b \c{PUNPCKLBW} would return \c{0x3B3A2B2A1B1A0B0A}.

\b \c{PUNPCKLWD} would return \c{0x3B2B3A2A1B0B1A0A}.

\b \c{PUNPCKLDQ} would return \c{0x3B2B1B0B3A2A1A0A}.


\S{insPUSH} \i\c{PUSH}: Push Data on Stack

\c PUSH reg16                    ; o16 50+r             [8086]
\c PUSH reg32                    ; o32 50+r             [386]

\c PUSH r/m16                    ; o16 FF /6            [8086]
\c PUSH r/m32                    ; o32 FF /6            [386]

\c PUSH CS                       ; 0E                   [8086]
\c PUSH DS                       ; 1E                   [8086]
\c PUSH ES                       ; 06                   [8086]
\c PUSH SS                       ; 16                   [8086]
\c PUSH FS                       ; 0F A0                [386]
\c PUSH GS                       ; 0F A8                [386]

\c PUSH imm8                     ; 6A ib                [186]
\c PUSH imm16                    ; o16 68 iw            [186]
\c PUSH imm32                    ; o32 68 id            [386]

\c{PUSH} decrements the stack pointer (\c{SP} or \c{ESP}) by 2 or 4,
and then stores the given value at \c{[SS:SP]} or \c{[SS:ESP]}.

The address-size attribute of the instruction determines whether
\c{SP} or \c{ESP} is used as the stack pointer: to deliberately
override the default given by the \c{BITS} setting, you can use an
\i\c{a16} or \i\c{a32} prefix.

The operand-size attribute of the instruction determines whether the
stack pointer is decremented by 2 or 4: this means that segment
register pushes in \c{BITS 32} mode will push 4 bytes on the stack,
of which the upper two are undefined. If you need to override that,
you can use an \i\c{o16} or \i\c{o32} prefix.

The above opcode listings give two forms for general-purpose
\i{register push} instructions: for example, \c{PUSH BX} has the two
forms \c{53} and \c{FF F3}. NASM will always generate the shorter
form when given \c{PUSH BX}. NDISASM will disassemble both.

Unlike the undocumented and barely supported \c{POP CS}, \c{PUSH CS}
is a perfectly valid and sensible instruction, supported on all
processors.

The instruction \c{PUSH SP} may be used to distinguish an 8086 from
later processors: on an 8086, the value of \c{SP} stored is the
value it has \e{after} the push instruction, whereas on later
processors it is the value \e{before} the push instruction.


\S{insPUSHA} \i\c{PUSHAx}: Push All General-Purpose Registers

\c PUSHA                         ; 60                   [186]
\c PUSHAD                        ; o32 60               [386]
\c PUSHAW                        ; o16 60               [186]

\c{PUSHAW} pushes, in succession, \c{AX}, \c{CX}, \c{DX}, \c{BX},
\c{SP}, \c{BP}, \c{SI} and \c{DI} on the stack, decrementing the
stack pointer by a total of 16.

\c{PUSHAD} pushes, in succession, \c{EAX}, \c{ECX}, \c{EDX},
\c{EBX}, \c{ESP}, \c{EBP}, \c{ESI} and \c{EDI} on the stack,
decrementing the stack pointer by a total of 32.

In both cases, the value of \c{SP} or \c{ESP} pushed is its
\e{original} value, as it had before the instruction was executed.

\c{PUSHA} is an alias mnemonic for either \c{PUSHAW} or \c{PUSHAD},
depending on the current \c{BITS} setting.

Note that the registers are pushed in order of their numeric values
in opcodes (see \k{iref-rv}).

See also \c{POPA} (\k{insPOPA}).


\S{insPUSHF} \i\c{PUSHFx}: Push Flags Register

\c PUSHF                         ; 9C                   [8086]
\c PUSHFD                        ; o32 9C               [386]
\c PUSHFW                        ; o16 9C               [8086]

\b \c{PUSHFW} pushes the bottom 16 bits of the flags register 
(or the whole flags register, on processors below a 386) onto
the stack.

\b \c{PUSHFD} pushes the entire flags register onto the stack.

\c{PUSHF} is an alias mnemonic for either \c{PUSHFW} or \c{PUSHFD},
depending on the current \c{BITS} setting.

See also \c{POPF} (\k{insPOPF}).


\S{insPXOR} \i\c{PXOR}: MMX Bitwise XOR

\c PXOR mm1,mm2/m64              ; 0F EF /r             [PENT,MMX]
\c PXOR xmm1,xmm2/m128           ; 66 0F EF /r     [WILLAMETTE,SSE2]

\c{PXOR} performs a bitwise XOR operation between its two operands
(i.e. each bit of the result is 1 if and only if exactly one of the
corresponding bits of the two inputs was 1), and stores the result
in the destination (first) operand.


\S{insRCL} \i\c{RCL}, \i\c{RCR}: Bitwise Rotate through Carry Bit

\c RCL r/m8,1                    ; D0 /2                [8086]
\c RCL r/m8,CL                   ; D2 /2                [8086]
\c RCL r/m8,imm8                 ; C0 /2 ib             [186]
\c RCL r/m16,1                   ; o16 D1 /2            [8086]
\c RCL r/m16,CL                  ; o16 D3 /2            [8086]
\c RCL r/m16,imm8                ; o16 C1 /2 ib         [186]
\c RCL r/m32,1                   ; o32 D1 /2            [386]
\c RCL r/m32,CL                  ; o32 D3 /2            [386]
\c RCL r/m32,imm8                ; o32 C1 /2 ib         [386]

\c RCR r/m8,1                    ; D0 /3                [8086]
\c RCR r/m8,CL                   ; D2 /3                [8086]
\c RCR r/m8,imm8                 ; C0 /3 ib             [186]
\c RCR r/m16,1                   ; o16 D1 /3            [8086]
\c RCR r/m16,CL                  ; o16 D3 /3            [8086]
\c RCR r/m16,imm8                ; o16 C1 /3 ib         [186]
\c RCR r/m32,1                   ; o32 D1 /3            [386]
\c RCR r/m32,CL                  ; o32 D3 /3            [386]
\c RCR r/m32,imm8                ; o32 C1 /3 ib         [386]

\c{RCL} and \c{RCR} perform a 9-bit, 17-bit or 33-bit bitwise
rotation operation, involving the given source/destination (first)
operand and the carry bit. Thus, for example, in the operation
\c{RCL AL,1}, a 9-bit rotation is performed in which \c{AL} is
shifted left by 1, the top bit of \c{AL} moves into the carry flag,
and the original value of the carry flag is placed in the low bit of
\c{AL}.

The number of bits to rotate by is given by the second operand. Only
the bottom five bits of the rotation count are considered by
processors above the 8086.

You can force the longer (286 and upwards, beginning with a \c{C1}
byte) form of \c{RCL foo,1} by using a \c{BYTE} prefix: \c{RCL
foo,BYTE 1}. Similarly with \c{RCR}.


\S{insRCPPS} \i\c{RCPPS}: Packed Single-Precision FP Reciprocal

\c RCPPS xmm1,xmm2/m128          ; 0F 53 /r        [KATMAI,SSE]

\c{RCPPS} returns an approximation of the reciprocal of the packed
single-precision FP values from xmm2/m128. The maximum error for this
approximation is: |Error| <= 1.5 x 2^-12


\S{insRCPSS} \i\c{RCPSS}: Scalar Single-Precision FP Reciprocal

\c RCPSS xmm1,xmm2/m128          ; F3 0F 53 /r     [KATMAI,SSE]

\c{RCPSS} returns an approximation of the reciprocal of the lower
single-precision FP value from xmm2/m32; the upper three fields are
passed through from xmm1. The maximum error for this approximation is:
|Error| <= 1.5 x 2^-12


\S{insRDMSR} \i\c{RDMSR}: Read Model-Specific Registers

\c RDMSR                         ; 0F 32                [PENT,PRIV]

\c{RDMSR} reads the processor Model-Specific Register (MSR) whose
index is stored in \c{ECX}, and stores the result in \c{EDX:EAX}.
See also \c{WRMSR} (\k{insWRMSR}).


\S{insRDPMC} \i\c{RDPMC}: Read Performance-Monitoring Counters

\c RDPMC                         ; 0F 33                [P6]

\c{RDPMC} reads the processor performance-monitoring counter whose
index is stored in \c{ECX}, and stores the result in \c{EDX:EAX}.

This instruction is available on P6 and later processors and on MMX
class processors.


\S{insRDSHR} \i\c{RDSHR}: Read SMM Header Pointer Register

\c RDSHR r/m32                   ; 0F 36 /0        [386,CYRIX,SMM]

\c{RDSHR} reads the contents of the SMM header pointer register and
saves it to the destination operand, which can be either a 32 bit
memory location or a 32 bit register.

See also \c{WRSHR} (\k{insWRSHR}).


\S{insRDTSC} \i\c{RDTSC}: Read Time-Stamp Counter

\c RDTSC                         ; 0F 31                [PENT]

\c{RDTSC} reads the processor's time-stamp counter into \c{EDX:EAX}.


\S{insRET} \i\c{RET}, \i\c{RETF}, \i\c{RETN}: Return from Procedure Call

\c RET                           ; C3                   [8086]
\c RET imm16                     ; C2 iw                [8086]

\c RETF                          ; CB                   [8086]
\c RETF imm16                    ; CA iw                [8086]

\c RETN                          ; C3                   [8086]
\c RETN imm16                    ; C2 iw                [8086]

\b \c{RET}, and its exact synonym \c{RETN}, pop \c{IP} or \c{EIP} from
the stack and transfer control to the new address. Optionally, if a
numeric second operand is provided, they increment the stack pointer
by a further \c{imm16} bytes after popping the return address.

\b \c{RETF} executes a far return: after popping \c{IP}/\c{EIP}, it
then pops \c{CS}, and \e{then} increments the stack pointer by the
optional argument if present.


\S{insROL} \i\c{ROL}, \i\c{ROR}: Bitwise Rotate

\c ROL r/m8,1                    ; D0 /0                [8086]
\c ROL r/m8,CL                   ; D2 /0                [8086]
\c ROL r/m8,imm8                 ; C0 /0 ib             [186]
\c ROL r/m16,1                   ; o16 D1 /0            [8086]
\c ROL r/m16,CL                  ; o16 D3 /0            [8086]
\c ROL r/m16,imm8                ; o16 C1 /0 ib         [186]
\c ROL r/m32,1                   ; o32 D1 /0            [386]
\c ROL r/m32,CL                  ; o32 D3 /0            [386]
\c ROL r/m32,imm8                ; o32 C1 /0 ib         [386]

\c ROR r/m8,1                    ; D0 /1                [8086]
\c ROR r/m8,CL                   ; D2 /1                [8086]
\c ROR r/m8,imm8                 ; C0 /1 ib             [186]
\c ROR r/m16,1                   ; o16 D1 /1            [8086]
\c ROR r/m16,CL                  ; o16 D3 /1            [8086]
\c ROR r/m16,imm8                ; o16 C1 /1 ib         [186]
\c ROR r/m32,1                   ; o32 D1 /1            [386]
\c ROR r/m32,CL                  ; o32 D3 /1            [386]
\c ROR r/m32,imm8                ; o32 C1 /1 ib         [386]

\c{ROL} and \c{ROR} perform a bitwise rotation operation on the given
source/destination (first) operand. Thus, for example, in the
operation \c{ROL AL,1}, an 8-bit rotation is performed in which
\c{AL} is shifted left by 1 and the original top bit of \c{AL} moves
round into the low bit.

The number of bits to rotate by is given by the second operand. Only
the bottom five bits of the rotation count are considered by processors
above the 8086.

You can force the longer (286 and upwards, beginning with a \c{C1}
byte) form of \c{ROL foo,1} by using a \c{BYTE} prefix: \c{ROL
foo,BYTE 1}. Similarly with \c{ROR}.


\S{insRSDC} \i\c{RSDC}: Restore Segment Register and Descriptor

\c RSDC segreg,m80               ; 0F 79 /r        [486,CYRIX,SMM]

\c{RSDC} restores a segment register (DS, ES, FS, GS, or SS) from mem80,
and sets up its descriptor.


\S{insRSLDT} \i\c{RSLDT}: Restore Segment Register and Descriptor

\c RSLDT m80                     ; 0F 7B /0        [486,CYRIX,SMM]

\c{RSLDT} restores the Local Descriptor Table (LDTR) from mem80.


\S{insRSM} \i\c{RSM}: Resume from System-Management Mode

\c RSM                           ; 0F AA                [PENT]

\c{RSM} returns the processor to its normal operating mode when it
was in System-Management Mode.


\S{insRSQRTPS} \i\c{RSQRTPS}: Packed Single-Precision FP Square Root Reciprocal

\c RSQRTPS xmm1,xmm2/m128        ; 0F 52 /r        [KATMAI,SSE]

\c{RSQRTPS} computes the approximate reciprocals of the square
roots of the packed single-precision floating-point values in the
source and stores the results in xmm1. The maximum error for this
approximation is: |Error| <= 1.5 x 2^-12


\S{insRSQRTSS} \i\c{RSQRTSS}: Scalar Single-Precision FP Square Root Reciprocal

\c RSQRTSS xmm1,xmm2/m128        ; F3 0F 52 /r     [KATMAI,SSE]

\c{RSQRTSS} returns an approximation of the reciprocal of the
square root of the lowest order single-precision FP value from
the source, and stores it in the low doubleword of the destination
register. The upper three fields of xmm1 are preserved. The maximum
error for this approximation is: |Error| <= 1.5 x 2^-12


\S{insRSTS} \i\c{RSTS}: Restore TSR and Descriptor

\c RSTS m80                      ; 0F 7D /0        [486,CYRIX,SMM]

\c{RSTS} restores Task State Register (TSR) from mem80.


\S{insSAHF} \i\c{SAHF}: Store AH to Flags

\c SAHF                          ; 9E                   [8086]

\c{SAHF} sets the low byte of the flags word according to the
contents of the \c{AH} register.

The operation of \c{SAHF} is:

\c  AH --> SF:ZF:0:AF:0:PF:1:CF

See also \c{LAHF} (\k{insLAHF}).


\S{insSAL} \i\c{SAL}, \i\c{SAR}: Bitwise Arithmetic Shifts

\c SAL r/m8,1                    ; D0 /4                [8086]
\c SAL r/m8,CL                   ; D2 /4                [8086]
\c SAL r/m8,imm8                 ; C0 /4 ib             [186]
\c SAL r/m16,1                   ; o16 D1 /4            [8086]
\c SAL r/m16,CL                  ; o16 D3 /4            [8086]
\c SAL r/m16,imm8                ; o16 C1 /4 ib         [186]
\c SAL r/m32,1                   ; o32 D1 /4            [386]
\c SAL r/m32,CL                  ; o32 D3 /4            [386]
\c SAL r/m32,imm8                ; o32 C1 /4 ib         [386]

\c SAR r/m8,1                    ; D0 /7                [8086]
\c SAR r/m8,CL                   ; D2 /7                [8086]
\c SAR r/m8,imm8                 ; C0 /7 ib             [186]
\c SAR r/m16,1                   ; o16 D1 /7            [8086]
\c SAR r/m16,CL                  ; o16 D3 /7            [8086]
\c SAR r/m16,imm8                ; o16 C1 /7 ib         [186]
\c SAR r/m32,1                   ; o32 D1 /7            [386]
\c SAR r/m32,CL                  ; o32 D3 /7            [386]
\c SAR r/m32,imm8                ; o32 C1 /7 ib         [386]

\c{SAL} and \c{SAR} perform an arithmetic shift operation on the given
source/destination (first) operand. The vacated bits are filled with
zero for \c{SAL}, and with copies of the original high bit of the
source operand for \c{SAR}.

\c{SAL} is a synonym for \c{SHL} (see \k{insSHL}). NASM will
assemble either one to the same code, but NDISASM will always
disassemble that code as \c{SHL}.

The number of bits to shift by is given by the second operand. Only
the bottom five bits of the shift count are considered by processors
above the 8086.

You can force the longer (286 and upwards, beginning with a \c{C1}
byte) form of \c{SAL foo,1} by using a \c{BYTE} prefix: \c{SAL
foo,BYTE 1}. Similarly with \c{SAR}.


\S{insSALC} \i\c{SALC}: Set AL from Carry Flag

\c SALC                          ; D6                  [8086,UNDOC]

\c{SALC} is an early undocumented instruction similar in concept to
\c{SETcc} (\k{insSETcc}). Its function is to set \c{AL} to zero if
the carry flag is clear, or to \c{0xFF} if it is set.


\S{insSBB} \i\c{SBB}: Subtract with Borrow

\c SBB r/m8,reg8                 ; 18 /r                [8086]
\c SBB r/m16,reg16               ; o16 19 /r            [8086]
\c SBB r/m32,reg32               ; o32 19 /r            [386]

\c SBB reg8,r/m8                 ; 1A /r                [8086]
\c SBB reg16,r/m16               ; o16 1B /r            [8086]
\c SBB reg32,r/m32               ; o32 1B /r            [386]

\c SBB r/m8,imm8                 ; 80 /3 ib             [8086]
\c SBB r/m16,imm16               ; o16 81 /3 iw         [8086]
\c SBB r/m32,imm32               ; o32 81 /3 id         [386]

\c SBB r/m16,imm8                ; o16 83 /3 ib         [8086]
\c SBB r/m32,imm8                ; o32 83 /3 ib         [386]

\c SBB AL,imm8                   ; 1C ib                [8086]
\c SBB AX,imm16                  ; o16 1D iw            [8086]
\c SBB EAX,imm32                 ; o32 1D id            [386]

\c{SBB} performs integer subtraction: it subtracts its second
operand, plus the value of the carry flag, from its first, and
leaves the result in its destination (first) operand. The flags are
set according to the result of the operation: in particular, the
carry flag is affected and can be used by a subsequent \c{SBB}
instruction.

In the forms with an 8-bit immediate second operand and a longer
first operand, the second operand is considered to be signed, and is
sign-extended to the length of the first operand. In these cases,
the \c{BYTE} qualifier is necessary to force NASM to generate this
form of the instruction.

To subtract one number from another without also subtracting the
contents of the carry flag, use \c{SUB} (\k{insSUB}).


\S{insSCASB} \i\c{SCASB}, \i\c{SCASW}, \i\c{SCASD}: Scan String

\c SCASB                         ; AE                   [8086]
\c SCASW                         ; o16 AF               [8086]
\c SCASD                         ; o32 AF               [386]

\c{SCASB} compares the byte in \c{AL} with the byte at \c{[ES:DI]}
or \c{[ES:EDI]}, and sets the flags accordingly. It then increments
or decrements (depending on the direction flag: increments if the
flag is clear, decrements if it is set) \c{DI} (or \c{EDI}).

The register used is \c{DI} if the address size is 16 bits, and
\c{EDI} if it is 32 bits. If you need to use an address size not
equal to the current \c{BITS} setting, you can use an explicit
\i\c{a16} or \i\c{a32} prefix.

Segment override prefixes have no effect for this instruction: the
use of \c{ES} for the load from \c{[DI]} or \c{[EDI]} cannot be
overridden.

\c{SCASW} and \c{SCASD} work in the same way, but they compare a
word to \c{AX} or a doubleword to \c{EAX} instead of a byte to
\c{AL}, and increment or decrement the addressing registers by 2 or
4 instead of 1.

The \c{REPE} and \c{REPNE} prefixes (equivalently, \c{REPZ} and
\c{REPNZ}) may be used to repeat the instruction up to \c{CX} (or
\c{ECX} - again, the address size chooses which) times until the
first unequal or equal byte is found.


\S{insSETcc} \i\c{SETcc}: Set Register from Condition

\c SETcc r/m8                    ; 0F 90+cc /2          [386]

\c{SETcc} sets the given 8-bit operand to zero if its condition is
not satisfied, and to 1 if it is.


\S{insSFENCE} \i\c{SFENCE}: Store Fence

\c SFENCE                 ; 0F AE /7               [KATMAI]

\c{SFENCE} performs a serialising operation on all writes to memory
that were issued before the \c{SFENCE} instruction. This guarantees that
all memory writes before the \c{SFENCE} instruction are visible before any
writes after the \c{SFENCE} instruction.

\c{SFENCE} is ordered respective to other \c{SFENCE} instruction, \c{MFENCE},
any memory write and any other serialising instruction (such as \c{CPUID}).

Weakly ordered memory types can be used to achieve higher processor
performance through such techniques as out-of-order issue,
write-combining, and write-collapsing. The degree to which a consumer
of data recognizes or knows that the data is weakly ordered varies
among applications and may be unknown to the producer of this data.
The \c{SFENCE} instruction provides a performance-efficient way of
insuring store ordering between routines that produce weakly-ordered
results and routines that consume this data.

\c{SFENCE} uses the following ModRM encoding:

\c           Mod (7:6)        = 11B
\c           Reg/Opcode (5:3) = 111B
\c           R/M (2:0)        = 000B

All other ModRM encodings are defined to be reserved, and use
of these encodings risks incompatibility with future processors.

See also \c{LFENCE} (\k{insLFENCE}) and \c{MFENCE} (\k{insMFENCE}).


\S{insSGDT} \i\c{SGDT}, \i\c{SIDT}, \i\c{SLDT}: Store Descriptor Table Pointers

\c SGDT mem                      ; 0F 01 /0             [286,PRIV]
\c SIDT mem                      ; 0F 01 /1             [286,PRIV]
\c SLDT r/m16                    ; 0F 00 /0             [286,PRIV]

\c{SGDT} and \c{SIDT} both take a 6-byte memory area as an operand:
they store the contents of the GDTR (global descriptor table
register) or IDTR (interrupt descriptor table register) into that
area as a 32-bit linear address and a 16-bit size limit from that
area (in that order). These are the only instructions which directly
use \e{linear} addresses, rather than segment/offset pairs.

\c{SLDT} stores the segment selector corresponding to the LDT (local
descriptor table) into the given operand.

See also \c{LGDT}, \c{LIDT} and \c{LLDT} (\k{insLGDT}).


\S{insSHL} \i\c{SHL}, \i\c{SHR}: Bitwise Logical Shifts

\c SHL r/m8,1                    ; D0 /4                [8086]
\c SHL r/m8,CL                   ; D2 /4                [8086]
\c SHL r/m8,imm8                 ; C0 /4 ib             [186]
\c SHL r/m16,1                   ; o16 D1 /4            [8086]
\c SHL r/m16,CL                  ; o16 D3 /4            [8086]
\c SHL r/m16,imm8                ; o16 C1 /4 ib         [186]
\c SHL r/m32,1                   ; o32 D1 /4            [386]
\c SHL r/m32,CL                  ; o32 D3 /4            [386]
\c SHL r/m32,imm8                ; o32 C1 /4 ib         [386]

\c SHR r/m8,1                    ; D0 /5                [8086]
\c SHR r/m8,CL                   ; D2 /5                [8086]
\c SHR r/m8,imm8                 ; C0 /5 ib             [186]
\c SHR r/m16,1                   ; o16 D1 /5            [8086]
\c SHR r/m16,CL                  ; o16 D3 /5            [8086]
\c SHR r/m16,imm8                ; o16 C1 /5 ib         [186]
\c SHR r/m32,1                   ; o32 D1 /5            [386]
\c SHR r/m32,CL                  ; o32 D3 /5            [386]
\c SHR r/m32,imm8                ; o32 C1 /5 ib         [386]

\c{SHL} and \c{SHR} perform a logical shift operation on the given
source/destination (first) operand. The vacated bits are filled with
zero.

A synonym for \c{SHL} is \c{SAL} (see \k{insSAL}). NASM will
assemble either one to the same code, but NDISASM will always
disassemble that code as \c{SHL}.

The number of bits to shift by is given by the second operand. Only
the bottom five bits of the shift count are considered by processors
above the 8086.

You can force the longer (286 and upwards, beginning with a \c{C1}
byte) form of \c{SHL foo,1} by using a \c{BYTE} prefix: \c{SHL
foo,BYTE 1}. Similarly with \c{SHR}.


\S{insSHLD} \i\c{SHLD}, \i\c{SHRD}: Bitwise Double-Precision Shifts

\c SHLD r/m16,reg16,imm8         ; o16 0F A4 /r ib      [386]
\c SHLD r/m16,reg32,imm8         ; o32 0F A4 /r ib      [386]
\c SHLD r/m16,reg16,CL           ; o16 0F A5 /r         [386]
\c SHLD r/m16,reg32,CL           ; o32 0F A5 /r         [386]

\c SHRD r/m16,reg16,imm8         ; o16 0F AC /r ib      [386]
\c SHRD r/m32,reg32,imm8         ; o32 0F AC /r ib      [386]
\c SHRD r/m16,reg16,CL           ; o16 0F AD /r         [386]
\c SHRD r/m32,reg32,CL           ; o32 0F AD /r         [386]

\b \c{SHLD} performs a double-precision left shift. It notionally
places its second operand to the right of its first, then shifts
the entire bit string thus generated to the left by a number of
bits specified in the third operand. It then updates only the
\e{first} operand according to the result of this. The second
operand is not modified.

\b \c{SHRD} performs the corresponding right shift: it notionally
places the second operand to the \e{left} of the first, shifts the
whole bit string right, and updates only the first operand.

For example, if \c{EAX} holds \c{0x01234567} and \c{EBX} holds
\c{0x89ABCDEF}, then the instruction \c{SHLD EAX,EBX,4} would update
\c{EAX} to hold \c{0x12345678}. Under the same conditions, \c{SHRD
EAX,EBX,4} would update \c{EAX} to hold \c{0xF0123456}.

The number of bits to shift by is given by the third operand. Only
the bottom five bits of the shift count are considered.


\S{insSHUFPD} \i\c{SHUFPD}: Shuffle Packed Double-Precision FP Values

\c SHUFPD xmm1,xmm2/m128,imm8    ; 66 0F C6 /r ib  [WILLAMETTE,SSE2]

\c{SHUFPD} moves one of the packed double-precision FP values from
the destination operand into the low quadword of the destination
operand; the upper quadword is generated by moving one of the
double-precision FP values from the source operand into the
destination. The select (third) operand selects which of the values
are moved to the destination register.

The select operand is an 8-bit immediate: bit 0 selects which value
is moved from the destination operand to the result (where 0 selects
the low quadword and 1 selects the high quadword) and bit 1 selects
which value is moved from the source operand to the result.
Bits 2 through 7 of the shuffle operand are reserved.


\S{insSHUFPS} \i\c{SHUFPS}: Shuffle Packed Single-Precision FP Values

\c SHUFPS xmm1,xmm2/m128,imm8    ; 0F C6 /r ib     [KATMAI,SSE]

\c{SHUFPS} moves two of the packed single-precision FP values from
the destination operand into the low quadword of the destination
operand; the upper quadword is generated by moving two of the
single-precision FP values from the source operand into the
destination. The select (third) operand selects which of the
values are moved to the destination register.

The select operand is an 8-bit immediate: bits 0 and 1 select the
value to be moved from the destination operand the low doubleword of
the result, bits 2 and 3 select the value to be moved from the
destination operand the second doubleword of the result, bits 4 and
5 select the value to be moved from the source operand the third
doubleword of the result, and bits 6 and 7 select the value to be
moved from the source operand to the high doubleword of the result.


\S{insSMI} \i\c{SMI}: System Management Interrupt

\c SMI                           ; F1                   [386,UNDOC]

\c{SMI} puts some AMD processors into SMM mode. It is available on some
386 and 486 processors, and is only available when DR7 bit 12 is set,
otherwise it generates an Int 1.


\S{insSMINT} \i\c{SMINT}, \i\c{SMINTOLD}: Software SMM Entry (CYRIX)

\c SMINT                         ; 0F 38                [PENT,CYRIX]
\c SMINTOLD                      ; 0F 7E                [486,CYRIX]

\c{SMINT} puts the processor into SMM mode. The CPU state information is
saved in the SMM memory header, and then execution begins at the SMM base
address.

\c{SMINTOLD} is the same as \c{SMINT}, but was the opcode used on the 486.

This pair of opcodes are specific to the Cyrix and compatible range of
processors (Cyrix, IBM, Via).


\S{insSMSW} \i\c{SMSW}: Store Machine Status Word

\c SMSW r/m16                    ; 0F 01 /4             [286,PRIV]

\c{SMSW} stores the bottom half of the \c{CR0} control register (or
the Machine Status Word, on 286 processors) into the destination
operand. See also \c{LMSW} (\k{insLMSW}).

For 32-bit code, this would store all of \c{CR0} in the specified
register (or the bottom 16 bits if the destination is a memory location),
 without needing an operand size override byte.


\S{insSQRTPD} \i\c{SQRTPD}: Packed Double-Precision FP Square Root

\c SQRTPD xmm1,xmm2/m128         ; 66 0F 51 /r     [WILLAMETTE,SSE2]

\c{SQRTPD} calculates the square root of the packed double-precision
FP value from the source operand, and stores the double-precision
results in the destination register.


\S{insSQRTPS} \i\c{SQRTPS}: Packed Single-Precision FP Square Root

\c SQRTPS xmm1,xmm2/m128         ; 0F 51 /r        [KATMAI,SSE]

\c{SQRTPS} calculates the square root of the packed single-precision
FP value from the source operand, and stores the single-precision
results in the destination register.


\S{insSQRTSD} \i\c{SQRTSD}: Scalar Double-Precision FP Square Root

\c SQRTSD xmm1,xmm2/m128         ; F2 0F 51 /r     [WILLAMETTE,SSE2]

\c{SQRTSD} calculates the square root of the low-order double-precision
FP value from the source operand, and stores the double-precision
result in the destination register. The high-quadword remains unchanged.


\S{insSQRTSS} \i\c{SQRTSS}: Scalar Single-Precision FP Square Root

\c SQRTSS xmm1,xmm2/m128         ; F3 0F 51 /r     [KATMAI,SSE]

\c{SQRTSS} calculates the square root of the low-order single-precision
FP value from the source operand, and stores the single-precision
result in the destination register. The three high doublewords remain
unchanged.


\S{insSTC} \i\c{STC}, \i\c{STD}, \i\c{STI}: Set Flags

\c STC                           ; F9                   [8086]
\c STD                           ; FD                   [8086]
\c STI                           ; FB                   [8086]

These instructions set various flags. \c{STC} sets the carry flag;
\c{STD} sets the direction flag; and \c{STI} sets the interrupt flag
(thus enabling interrupts).

To clear the carry, direction, or interrupt flags, use the \c{CLC},
\c{CLD} and \c{CLI} instructions (\k{insCLC}). To invert the carry
flag, use \c{CMC} (\k{insCMC}).


\S{insSTMXCSR} \i\c{STMXCSR}: Store Streaming SIMD Extension
 Control/Status

\c STMXCSR m32                   ; 0F AE /3        [KATMAI,SSE]

\c{STMXCSR} stores the contents of the \c{MXCSR} control/status
register to the specified memory location. \c{MXCSR} is used to
enable masked/unmasked exception handling, to set rounding modes,
to set flush-to-zero mode, and to view exception status flags.
The reserved bits in the \c{MXCSR} register are stored as 0s.

For details of the \c{MXCSR} register, see the Intel processor docs.

See also \c{LDMXCSR} (\k{insLDMXCSR}).


\S{insSTOSB} \i\c{STOSB}, \i\c{STOSW}, \i\c{STOSD}: Store Byte to String

\c STOSB                         ; AA                   [8086]
\c STOSW                         ; o16 AB               [8086]
\c STOSD                         ; o32 AB               [386]

\c{STOSB} stores the byte in \c{AL} at \c{[ES:DI]} or \c{[ES:EDI]},
and sets the flags accordingly. It then increments or decrements
(depending on the direction flag: increments if the flag is clear,
decrements if it is set) \c{DI} (or \c{EDI}).

The register used is \c{DI} if the address size is 16 bits, and
\c{EDI} if it is 32 bits. If you need to use an address size not
equal to the current \c{BITS} setting, you can use an explicit
\i\c{a16} or \i\c{a32} prefix.

Segment override prefixes have no effect for this instruction: the
use of \c{ES} for the store to \c{[DI]} or \c{[EDI]} cannot be
overridden.

\c{STOSW} and \c{STOSD} work in the same way, but they store the
word in \c{AX} or the doubleword in \c{EAX} instead of the byte in
\c{AL}, and increment or decrement the addressing registers by 2 or
4 instead of 1.

The \c{REP} prefix may be used to repeat the instruction \c{CX} (or
\c{ECX} - again, the address size chooses which) times.


\S{insSTR} \i\c{STR}: Store Task Register

\c STR r/m16                     ; 0F 00 /1             [286,PRIV]

\c{STR} stores the segment selector corresponding to the contents of
the Task Register into its operand. When the operand size is 32 bit and
the destination is a register, the upper 16-bits are cleared to 0s. 
When the destination operand is a memory location, 16 bits are
written regardless of the  operand size.


\S{insSUB} \i\c{SUB}: Subtract Integers

\c SUB r/m8,reg8                 ; 28 /r                [8086]
\c SUB r/m16,reg16               ; o16 29 /r            [8086]
\c SUB r/m32,reg32               ; o32 29 /r            [386]

\c SUB reg8,r/m8                 ; 2A /r                [8086]
\c SUB reg16,r/m16               ; o16 2B /r            [8086]
\c SUB reg32,r/m32               ; o32 2B /r            [386]

\c SUB r/m8,imm8                 ; 80 /5 ib             [8086]
\c SUB r/m16,imm16               ; o16 81 /5 iw         [8086]
\c SUB r/m32,imm32               ; o32 81 /5 id         [386]

\c SUB r/m16,imm8                ; o16 83 /5 ib         [8086]
\c SUB r/m32,imm8                ; o32 83 /5 ib         [386]

\c SUB AL,imm8                   ; 2C ib                [8086]
\c SUB AX,imm16                  ; o16 2D iw            [8086]
\c SUB EAX,imm32                 ; o32 2D id            [386]

\c{SUB} performs integer subtraction: it subtracts its second
operand from its first, and leaves the result in its destination
(first) operand. The flags are set according to the result of the
operation: in particular, the carry flag is affected and can be used
by a subsequent \c{SBB} instruction (\k{insSBB}).

In the forms with an 8-bit immediate second operand and a longer
first operand, the second operand is considered to be signed, and is
sign-extended to the length of the first operand. In these cases,
the \c{BYTE} qualifier is necessary to force NASM to generate this
form of the instruction.


\S{insSUBPD} \i\c{SUBPD}: Packed Double-Precision FP Subtract

\c SUBPD xmm1,xmm2/m128          ; 66 0F 5C /r     [WILLAMETTE,SSE2]

\c{SUBPD} subtracts the packed double-precision FP values of
the source operand from those of the destination operand, and
stores the result in the destination operation.


\S{insSUBPS} \i\c{SUBPS}: Packed Single-Precision FP Subtract

\c SUBPS xmm1,xmm2/m128          ; 0F 5C /r        [KATMAI,SSE]

\c{SUBPS} subtracts the packed single-precision FP values of
the source operand from those of the destination operand, and
stores the result in the destination operation.


\S{insSUBSD} \i\c{SUBSD}: Scalar Single-FP Subtract

\c SUBSD xmm1,xmm2/m128          ; F2 0F 5C /r     [WILLAMETTE,SSE2]

\c{SUBSD} subtracts the low-order double-precision FP value of
the source operand from that of the destination operand, and
stores the result in the destination operation. The high
quadword is unchanged.


\S{insSUBSS} \i\c{SUBSS}: Scalar Single-FP Subtract

\c SUBSS xmm1,xmm2/m128          ; F3 0F 5C /r     [KATMAI,SSE]

\c{SUBSS} subtracts the low-order single-precision FP value of
the source operand from that of the destination operand, and
stores the result in the destination operation. The three high
doublewords are unchanged.


\S{insSVDC} \i\c{SVDC}: Save Segment Register and Descriptor

\c SVDC m80,segreg               ; 0F 78 /r        [486,CYRIX,SMM]

\c{SVDC} saves a segment register (DS, ES, FS, GS, or SS) and its
descriptor to mem80.


\S{insSVLDT} \i\c{SVLDT}: Save LDTR and Descriptor

\c SVLDT m80                     ; 0F 7A /0        [486,CYRIX,SMM]

\c{SVLDT} saves the Local Descriptor Table (LDTR) to mem80.


\S{insSVTS} \i\c{SVTS}: Save TSR and Descriptor

\c SVTS m80                      ; 0F 7C /0        [486,CYRIX,SMM]

\c{SVTS} saves the Task State Register (TSR) to mem80.


\S{insSYSCALL} \i\c{SYSCALL}: Call Operating System

\c SYSCALL                       ; 0F 05                [P6,AMD]

\c{SYSCALL} provides a fast method of transferring control to a fixed
entry point in an operating system.

\b The \c{EIP} register is copied into the \c{ECX} register.

\b Bits [31-0] of the 64-bit SYSCALL/SYSRET Target Address Register
(\c{STAR}) are copied into the \c{EIP} register.

\b Bits [47-32] of the \c{STAR} register specify the selector that is
copied into the \c{CS} register.

\b Bits [47-32]+1000b of the \c{STAR} register specify the selector that
is copied into the SS register.

The \c{CS} and \c{SS} registers should not be modified by the operating
system between the execution of the \c{SYSCALL} instruction and its
corresponding \c{SYSRET} instruction.

For more information, see the \c{SYSCALL and SYSRET Instruction Specification}
(AMD document number 21086.pdf).


\S{insSYSENTER} \i\c{SYSENTER}: Fast System Call

\c SYSENTER                      ; 0F 34                [P6]

\c{SYSENTER} executes a fast call to a level 0 system procedure or
routine. Before using this instruction, various MSRs need to be set
up:

\b \c{SYSENTER_CS_MSR} contains the 32-bit segment selector for the
privilege level 0 code segment. (This value is also used to compute
the segment selector of the privilege level 0 stack segment.)

\b \c{SYSENTER_EIP_MSR} contains the 32-bit offset into the privilege
level 0 code segment to the first instruction of the selected operating
procedure or routine.

\b \c{SYSENTER_ESP_MSR} contains the 32-bit stack pointer for the
privilege level 0 stack.

\c{SYSENTER} performs the following sequence of operations:

\b Loads the segment selector from the \c{SYSENTER_CS_MSR} into the
\c{CS} register.

\b Loads the instruction pointer from the \c{SYSENTER_EIP_MSR} into
the \c{EIP} register.

\b Adds 8 to the value in \c{SYSENTER_CS_MSR} and loads it into the
\c{SS} register.

\b Loads the stack pointer from the \c{SYSENTER_ESP_MSR} into the
\c{ESP} register.

\b Switches to privilege level 0.

\b Clears the \c{VM} flag in the \c{EFLAGS} register, if the flag
is set.

\b Begins executing the selected system procedure.

In particular, note that this instruction des not save the values of
\c{CS} or \c{(E)IP}. If you need to return to the calling code, you
need to write your code to cater for this.

For more information, see the Intel Architecture Software Developer's
Manual, Volume 2.


\S{insSYSEXIT} \i\c{SYSEXIT}: Fast Return From System Call

\c SYSEXIT                       ; 0F 35                [P6,PRIV]

\c{SYSEXIT} executes a fast return to privilege level 3 user code.
This instruction is a companion instruction to the \c{SYSENTER}
instruction, and can only be executed by privilege level 0 code.
Various registers need to be set up before calling this instruction:

\b \c{SYSENTER_CS_MSR} contains the 32-bit segment selector for the
privilege level 0 code segment in which the processor is currently
executing. (This value is used to compute the segment selectors for
the privilege level 3 code and stack segments.)

\b \c{EDX} contains the 32-bit offset into the privilege level 3 code
segment to the first instruction to be executed in the user code.

\b \c{ECX} contains the 32-bit stack pointer for the privilege level 3
stack.

\c{SYSEXIT} performs the following sequence of operations:

\b Adds 16 to the value in \c{SYSENTER_CS_MSR} and loads the sum into
the \c{CS} selector register.

\b Loads the instruction pointer from the \c{EDX} register into the
\c{EIP} register.

\b Adds 24 to the value in \c{SYSENTER_CS_MSR} and loads the sum
into the \c{SS} selector register.

\b Loads the stack pointer from the \c{ECX} register into the \c{ESP}
register.

\b Switches to privilege level 3.

\b Begins executing the user code at the \c{EIP} address.

For more information on the use of the \c{SYSENTER} and \c{SYSEXIT}
instructions, see the Intel Architecture Software Developer's
Manual, Volume 2.


\S{insSYSRET} \i\c{SYSRET}: Return From Operating System

\c SYSRET                        ; 0F 07                [P6,AMD,PRIV]

\c{SYSRET} is the return instruction used in conjunction with the
\c{SYSCALL} instruction to provide fast entry/exit to an operating system.

\b The \c{ECX} register, which points to the next sequential instruction
after the corresponding \c{SYSCALL} instruction, is copied into the \c{EIP}
register.

\b Bits [63-48] of the \c{STAR} register specify the selector that is copied
into the \c{CS} register.

\b Bits [63-48]+1000b of the \c{STAR} register specify the selector that is
copied into the \c{SS} register.

\b Bits [1-0] of the \c{SS} register are set to 11b (RPL of 3) regardless of
the value of bits [49-48] of the \c{STAR} register.

The \c{CS} and \c{SS} registers should not be modified by the operating
system between the execution of the \c{SYSCALL} instruction and its
corresponding \c{SYSRET} instruction.

For more information, see the \c{SYSCALL and SYSRET Instruction Specification}
(AMD document number 21086.pdf).


\S{insTEST} \i\c{TEST}: Test Bits (notional bitwise AND)

\c TEST r/m8,reg8                ; 84 /r                [8086]
\c TEST r/m16,reg16              ; o16 85 /r            [8086]
\c TEST r/m32,reg32              ; o32 85 /r            [386]

\c TEST r/m8,imm8                ; F6 /0 ib             [8086]
\c TEST r/m16,imm16              ; o16 F7 /0 iw         [8086]
\c TEST r/m32,imm32              ; o32 F7 /0 id         [386]

\c TEST AL,imm8                  ; A8 ib                [8086]
\c TEST AX,imm16                 ; o16 A9 iw            [8086]
\c TEST EAX,imm32                ; o32 A9 id            [386]

\c{TEST} performs a `mental' bitwise AND of its two operands, and
affects the flags as if the operation had taken place, but does not
store the result of the operation anywhere.


\S{insUCOMISD} \i\c{UCOMISD}: Unordered Scalar Double-Precision FP
compare and set EFLAGS

\c UCOMISD xmm1,xmm2/m128        ; 66 0F 2E /r     [WILLAMETTE,SSE2]

\c{UCOMISD} compares the low-order double-precision FP numbers in the
two operands, and sets the \c{ZF}, \c{PF} and \c{CF} bits in the
\c{EFLAGS} register. In addition, the \c{OF}, \c{SF} and \c{AF} bits
in the \c{EFLAGS} register are zeroed out. The unordered predicate
(\c{ZF}, \c{PF} and \c{CF} all set) is returned if either source
operand is a \c{NaN} (\c{qNaN} or \c{sNaN}).


\S{insUCOMISS} \i\c{UCOMISS}: Unordered Scalar Single-Precision FP
compare and set EFLAGS

\c UCOMISS xmm1,xmm2/m128        ; 0F 2E /r        [KATMAI,SSE]

\c{UCOMISS} compares the low-order single-precision FP numbers in the
two operands, and sets the \c{ZF}, \c{PF} and \c{CF} bits in the
\c{EFLAGS} register. In addition, the \c{OF}, \c{SF} and \c{AF} bits
in the \c{EFLAGS} register are zeroed out. The unordered predicate
(\c{ZF}, \c{PF} and \c{CF} all set) is returned if either source
operand is a \c{NaN} (\c{qNaN} or \c{sNaN}).


\S{insUD2} \i\c{UD0}, \i\c{UD1}, \i\c{UD2}: Undefined Instruction

\c UD0                           ; 0F FF                [186,UNDOC]
\c UD1                           ; 0F B9                [186,UNDOC]
\c UD2                           ; 0F 0B                [186]

\c{UDx} can be used to generate an invalid opcode exception, for testing
purposes.

\c{UD0} is specifically documented by AMD as being reserved for this
purpose.

\c{UD1} is documented by Intel as being available for this purpose.

\c{UD2} is specifically documented by Intel as being reserved for this
purpose. Intel document this as the preferred method of generating an
invalid opcode exception.

All these opcodes can be used to generate invalid opcode exceptions on
all currently available processors.


\S{insUMOV} \i\c{UMOV}: User Move Data

\c UMOV r/m8,reg8                ; 0F 10 /r             [386,UNDOC]
\c UMOV r/m16,reg16              ; o16 0F 11 /r         [386,UNDOC]
\c UMOV r/m32,reg32              ; o32 0F 11 /r         [386,UNDOC]

\c UMOV reg8,r/m8                ; 0F 12 /r             [386,UNDOC]
\c UMOV reg16,r/m16              ; o16 0F 13 /r         [386,UNDOC]
\c UMOV reg32,r/m32              ; o32 0F 13 /r         [386,UNDOC]

This undocumented instruction is used by in-circuit emulators to
access user memory (as opposed to host memory). It is used just like
an ordinary memory/register or register/register \c{MOV}
instruction, but accesses user space.

This instruction is only available on some AMD and IBM 386 and 486
processors.


\S{insUNPCKHPD} \i\c{UNPCKHPD}: Unpack and Interleave High Packed
Double-Precision FP Values

\c UNPCKHPD xmm1,xmm2/m128       ; 66 0F 15 /r     [WILLAMETTE,SSE2]

\c{UNPCKHPD} performs an interleaved unpack of the high-order data
elements of the source and destination operands, saving the result
in \c{xmm1}. It ignores the lower half of the sources.

The operation of this instruction is:

\c    dst[63-0]   := dst[127-64];
\c    dst[127-64] := src[127-64].


\S{insUNPCKHPS} \i\c{UNPCKHPS}: Unpack and Interleave High Packed
Single-Precision FP Values

\c UNPCKHPS xmm1,xmm2/m128       ; 0F 15 /r        [KATMAI,SSE]

\c{UNPCKHPS} performs an interleaved unpack of the high-order data
elements of the source and destination operands, saving the result
in \c{xmm1}. It ignores the lower half of the sources.

The operation of this instruction is:

\c    dst[31-0]   := dst[95-64];
\c    dst[63-32]  := src[95-64];
\c    dst[95-64]  := dst[127-96];
\c    dst[127-96] := src[127-96].


\S{insUNPCKLPD} \i\c{UNPCKLPD}: Unpack and Interleave Low Packed
Double-Precision FP Data

\c UNPCKLPD xmm1,xmm2/m128       ; 66 0F 14 /r     [WILLAMETTE,SSE2]

\c{UNPCKLPD} performs an interleaved unpack of the low-order data
elements of the source and destination operands, saving the result
in \c{xmm1}. It ignores the lower half of the sources.

The operation of this instruction is:

\c    dst[63-0]   := dst[63-0];
\c    dst[127-64] := src[63-0].


\S{insUNPCKLPS} \i\c{UNPCKLPS}: Unpack and Interleave Low Packed
Single-Precision FP Data

\c UNPCKLPS xmm1,xmm2/m128       ; 0F 14 /r        [KATMAI,SSE]

\c{UNPCKLPS} performs an interleaved unpack of the low-order data
elements of the source and destination operands, saving the result
in \c{xmm1}. It ignores the lower half of the sources.

The operation of this instruction is:

\c    dst[31-0]   := dst[31-0];
\c    dst[63-32]  := src[31-0];
\c    dst[95-64]  := dst[63-32];
\c    dst[127-96] := src[63-32].


\S{insVERR} \i\c{VERR}, \i\c{VERW}: Verify Segment Readability/Writability

\c VERR r/m16                    ; 0F 00 /4             [286,PRIV]

\c VERW r/m16                    ; 0F 00 /5             [286,PRIV]

\b \c{VERR} sets the zero flag if the segment specified by the selector
in its operand can be read from at the current privilege level.
Otherwise it is cleared.

\b \c{VERW} sets the zero flag if the segment can be written.


\S{insWAIT} \i\c{WAIT}: Wait for Floating-Point Processor

\c WAIT                          ; 9B                   [8086]
\c FWAIT                         ; 9B                   [8086]

\c{WAIT}, on 8086 systems with a separate 8087 FPU, waits for the
FPU to have finished any operation it is engaged in before
continuing main processor operations, so that (for example) an FPU
store to main memory can be guaranteed to have completed before the
CPU tries to read the result back out.

On higher processors, \c{WAIT} is unnecessary for this purpose, and
it has the alternative purpose of ensuring that any pending unmasked
FPU exceptions have happened before execution continues.


\S{insWBINVD} \i\c{WBINVD}: Write Back and Invalidate Cache

\c WBINVD                        ; 0F 09                [486]

\c{WBINVD} invalidates and empties the processor's internal caches,
and causes the processor to instruct external caches to do the same.
It writes the contents of the caches back to memory first, so no
data is lost. To flush the caches quickly without bothering to write
the data back first, use \c{INVD} (\k{insINVD}).


\S{insWRMSR} \i\c{WRMSR}: Write Model-Specific Registers

\c WRMSR                         ; 0F 30                [PENT]

\c{WRMSR} writes the value in \c{EDX:EAX} to the processor
Model-Specific Register (MSR) whose index is stored in \c{ECX}.
See also \c{RDMSR} (\k{insRDMSR}).


\S{insWRSHR} \i\c{WRSHR}: Write SMM Header Pointer Register

\c WRSHR r/m32                   ; 0F 37 /0        [386,CYRIX,SMM]

\c{WRSHR} loads the contents of either a 32-bit memory location or a
32-bit register into the SMM header pointer register.

See also \c{RDSHR} (\k{insRDSHR}).


\S{insXADD} \i\c{XADD}: Exchange and Add

\c XADD r/m8,reg8                ; 0F C0 /r             [486]
\c XADD r/m16,reg16              ; o16 0F C1 /r         [486]
\c XADD r/m32,reg32              ; o32 0F C1 /r         [486]

\c{XADD} exchanges the values in its two operands, and then adds
them together and writes the result into the destination (first)
operand. This instruction can be used with a \c{LOCK} prefix for
multi-processor synchronisation purposes.


\S{insXBTS} \i\c{XBTS}: Extract Bit String

\c XBTS reg16,r/m16              ; o16 0F A6 /r         [386,UNDOC]
\c XBTS reg32,r/m32              ; o32 0F A6 /r         [386,UNDOC]

The implied operation of this instruction is:

\c XBTS r/m16,reg16,AX,CL
\c XBTS r/m32,reg32,EAX,CL

Writes a bit string from the source operand to the destination. \c{CL}
indicates the number of bits to be copied, and \c{(E)AX} indicates the
low order bit offset in the source. The bits are written to the low
order bits of the destination register. For example, if \c{CL} is set
to 4 and \c{AX} (for 16-bit code) is set to 5, bits 5-8 of \c{src} will
be copied to bits 0-3 of \c{dst}. This instruction is very poorly
documented, and I have been unable to find any official source of
documentation on it.

\c{XBTS} is supported only on the early Intel 386s, and conflicts with
the opcodes for \c{CMPXCHG486} (on early Intel 486s). NASM supports it
only for completeness. Its counterpart is \c{IBTS} (see \k{insIBTS}).


\S{insXCHG} \i\c{XCHG}: Exchange

\c XCHG reg8,r/m8                ; 86 /r                [8086]
\c XCHG reg16,r/m8               ; o16 87 /r            [8086]
\c XCHG reg32,r/m32              ; o32 87 /r            [386]

\c XCHG r/m8,reg8                ; 86 /r                [8086]
\c XCHG r/m16,reg16              ; o16 87 /r            [8086]
\c XCHG r/m32,reg32              ; o32 87 /r            [386]

\c XCHG AX,reg16                 ; o16 90+r             [8086]
\c XCHG EAX,reg32                ; o32 90+r             [386]
\c XCHG reg16,AX                 ; o16 90+r             [8086]
\c XCHG reg32,EAX                ; o32 90+r             [386]

\c{XCHG} exchanges the values in its two operands. It can be used
with a \c{LOCK} prefix for purposes of multi-processor
synchronisation.

\c{XCHG AX,AX} or \c{XCHG EAX,EAX} (depending on the \c{BITS}
setting) generates the opcode \c{90h}, and so is a synonym for
\c{NOP} (\k{insNOP}).


\S{insXLATB} \i\c{XLATB}: Translate Byte in Lookup Table

\c XLAT                          ; D7                   [8086]
\c XLATB                         ; D7                   [8086]

\c{XLATB} adds the value in \c{AL}, treated as an unsigned byte, to
\c{BX} or \c{EBX}, and loads the byte from the resulting address (in
the segment specified by \c{DS}) back into \c{AL}.

The base register used is \c{BX} if the address size is 16 bits, and
\c{EBX} if it is 32 bits. If you need to use an address size not
equal to the current \c{BITS} setting, you can use an explicit
\i\c{a16} or \i\c{a32} prefix.

The segment register used to load from \c{[BX+AL]} or \c{[EBX+AL]}
can be overridden by using a segment register name as a prefix (for
example, \c{es xlatb}).


\S{insXOR} \i\c{XOR}: Bitwise Exclusive OR

\c XOR r/m8,reg8                 ; 30 /r                [8086]
\c XOR r/m16,reg16               ; o16 31 /r            [8086]
\c XOR r/m32,reg32               ; o32 31 /r            [386]

\c XOR reg8,r/m8                 ; 32 /r                [8086]
\c XOR reg16,r/m16               ; o16 33 /r            [8086]
\c XOR reg32,r/m32               ; o32 33 /r            [386]

\c XOR r/m8,imm8                 ; 80 /6 ib             [8086]
\c XOR r/m16,imm16               ; o16 81 /6 iw         [8086]
\c XOR r/m32,imm32               ; o32 81 /6 id         [386]

\c XOR r/m16,imm8                ; o16 83 /6 ib         [8086]
\c XOR r/m32,imm8                ; o32 83 /6 ib         [386]

\c XOR AL,imm8                   ; 34 ib                [8086]
\c XOR AX,imm16                  ; o16 35 iw            [8086]
\c XOR EAX,imm32                 ; o32 35 id            [386]

\c{XOR} performs a bitwise XOR operation between its two operands
(i.e. each bit of the result is 1 if and only if exactly one of the
corresponding bits of the two inputs was 1), and stores the result
in the destination (first) operand.

In the forms with an 8-bit immediate second operand and a longer
first operand, the second operand is considered to be signed, and is
sign-extended to the length of the first operand. In these cases,
the \c{BYTE} qualifier is necessary to force NASM to generate this
form of the instruction.

The \c{MMX} instruction \c{PXOR} (see \k{insPXOR}) performs the same
operation on the 64-bit \c{MMX} registers.


\S{insXORPD} \i\c{XORPD}: Bitwise Logical XOR of Double-Precision FP Values

\c XORPD xmm1,xmm2/m128          ; 66 0F 57 /r     [WILLAMETTE,SSE2]

\c{XORPD} returns a bit-wise logical XOR between the source and
destination operands, storing the result in the destination operand.


\S{insXORPS} \i\c{XORPS}: Bitwise Logical XOR of Single-Precision FP Values

\c XORPS xmm1,xmm2/m128          ; 0F 57 /r        [KATMAI,SSE]

\c{XORPS} returns a bit-wise logical XOR between the source and
destination operands, storing the result in the destination operand.


