# -*- coding: utf-8 -*-

#   The Netwide Assembler: NASM

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#     Appendix A: Intel 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 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,
# |http://www.intel.com/|.

# Instead, this appendix is intended primarily to provide documentation on
# the way the instructions may be used within NASM. For example, looking
# up |LOOP| will tell you that NASM allows |CX| or |ECX| to be specified
# as an optional second argument to the |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.


#       A.1 Key to Operand Specifications

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

#     * Registers: |reg8| denotes an 8-bit general purpose register,
#       |reg16| denotes a 16-bit general purpose register, and |reg32| a
#       32-bit one. |fpureg| denotes one of the eight FPU stack registers,
#       |mmxreg| denotes one of the eight 64-bit MMX registers, and
#       |segreg| denotes a segment register. In addition, some registers
#       (such as |AL|, |DX| or |ECX|) may be specified explicitly.
#     * Immediate operands: |imm| denotes a generic immediate operand.
#       |imm8|, |imm16| and |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, |ADD ESP,16| could be
#       interpreted as either |ADD r/m32,imm32| or |ADD r/m32,imm8|. NASM
#       chooses the former by default, and so you must specify |ADD
#       ESP,BYTE 16| for the latter.
#     * Memory references: |mem| denotes a generic memory reference;
#       |mem8|, |mem16|, |mem32|, |mem64| and |mem80| are used when the
#       operand needs to be a specific size. Again, a specifier is needed
#       in some cases: |DEC [address]| is ambiguous and will be rejected
#       by NASM. You must specify |DEC BYTE [address]|, |DEC WORD
#       [address]| or |DEC DWORD [address]| instead.
#     * Restricted memory references: one form of the |MOV| instruction
#       allows a memory address to be specified /without/ allowing the
#       normal range of register combinations and effective address
#       processing. This is denoted by |memoffs8|, |memoffs16| and
#       |memoffs32|.
#     * Register or memory choices: many instructions can accept either a
#       register /or/ a memory reference as an operand. |r/m8| is a
#       shorthand for |reg8/mem8|; similarly |r/m16| and |r/m32|. |r/m64|
#       is MMX-related, and is a shorthand for |mmxreg/mem64|.


#       A.2 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:

#     * A hex number, such as |3F|, indicates a fixed byte containing that
#       number.
#     * A hex number followed by |+r|, such as |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 |C8+r|, when the register operand is
#       EDX, generates the hex byte |CA|. Register values for specific
#       registers are given in section A.2.1 <#section-A.2.1>.
#     * A hex number followed by |+cc|, such as |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
#       |40+cc|, when the instruction contains the |NE| condition,
#       generates the hex byte |45|. Condition codes and their numeric
#       representations are given in section A.2.2 <#section-A.2.2>.
#     * A slash followed by a digit, such as |/2|, indicates that one of
#       the operands to the instruction is a memory address or register
#       (denoted |mem| or |r/m|, with an optional size). This is to be
#       encoded as an effective address, with a ModR/M byte, an optional
#       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 section A.2.3 <#section-A.2.3>.
#     * The code |/r| combines the above two: it indicates that one of the
#       operands is a memory address or |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 section A.2.3 <#section-A.2.3>; register
#       values are given in section A.2.1 <#section-A.2.1>.
#     * The codes |ib|, |iw| and |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.
#     * The codes |rb|, |rw| and |rd| indicate that one of the operands to
#       the instruction is an immediate value, and that the /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 |rw/rd| appears, it indicates that either |rw| or |rd|
#       should be used according to whether assembly is being performed in
#       |BITS 16| or |BITS 32| state respectively.
#     * The codes |ow| and |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 |MOV| instruction in place of the standard
#       effective-address mechanism. The displacement is encoded as a word
#       or doubleword. Again, |ow/od| denotes that |ow| or |od| should be
#       chosen according to the |BITS| setting.
#     * The codes |o16| and |o32| indicate that the given form of the
#       instruction should be assembled with operand size 16 or 32 bits.
#       In other words, |o16| indicates a |66| prefix in |BITS 32| state,
#       but generates no code in |BITS 16| state; and |o32| indicates a
#       |66| prefix in |BITS 16| state but generates nothing in |BITS 32|.
#     * The codes |a16| and |a32|, similarly to |o16| and |o32|, indicate
#       the address size of the given form of the instruction. Where this
#       does not match the |BITS| setting, a |67| prefix is required.


#         A.2.1 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.

# The encodings for the various classes of register are:

#     * 8-bit general registers: |AL| is 0, |CL| is 1, |DL| is 2, |BL| is
#       3, |AH| is 4, |CH| is 5, |DH| is 6, and |BH| is 7.
#     * 16-bit general registers: |AX| is 0, |CX| is 1, |DX| is 2, |BX| is
#       3, |SP| is 4, |BP| is 5, |SI| is 6, and |DI| is 7.
#     * 32-bit general registers: |EAX| is 0, |ECX| is 1, |EDX| is 2,
#       |EBX| is 3, |ESP| is 4, |EBP| is 5, |ESI| is 6, and |EDI| is 7.
#     * Segment registers: |ES| is 0, |CS| is 1, |SS| is 2, |DS| is 3,
#       |FS| is 4, and |GS| is 5.
#     * {Floating-point registers}: |ST0| is 0, |ST1| is 1, |ST2| is 2,
#       |ST3| is 3, |ST4| is 4, |ST5| is 5, |ST6| is 6, and |ST7| is 7.
#     * 64-bit MMX registers: |MM0| is 0, |MM1| is 1, |MM2| is 2, |MM3| is
#       3, |MM4| is 4, |MM5| is 5, |MM6| is 6, and |MM7| is 7.
#     * Control registers: |CR0| is 0, |CR2| is 2, |CR3| is 3, and |CR4|
#       is 4.
#     * Debug registers: |DR0| is 0, |DR1| is 1, |DR2| is 2, |DR3| is 3,
#       |DR6| is 6, and |DR7| is 7.
#     * Test registers: |TR3| is 3, |TR4| is 4, |TR5| is 5, |TR6| is 6,
#       and |TR7| is 7.

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


#         A.2.2 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.

#     * |O| is 0 (trigger if the overflow flag is set); |NO| is 1.
#     * |B|, |C| and |NAE| are 2 (trigger if the carry flag is set); |AE|,
#       |NB| and |NC| are 3.
#     * |E| and |Z| are 4 (trigger if the zero flag is set); |NE| and |NZ|
#       are 5.
#     * |BE| and |NA| are 6 (trigger if either of the carry or zero flags
#       is set); |A| and |NBE| are 7.
#     * |S| is 8 (trigger if the sign flag is set); |NS| is 9.
#     * |P| and |PE| are 10 (trigger if the parity flag is set); |NP| and
#       |PO| are 11.
#     * |L| and |NGE| are 12 (trigger if exactly one of the sign and
#       overflow flags is set); |GE| and |NL| are 13.
#     * |LE| and |NG| are 14 (trigger if either the zero flag is set, or
#       exactly one of the sign and overflow flags is set); |G| and |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.


#         A.2.3 Effective Address Encoding: ModR/M and SIB

# An 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 |mod| field, ranging from
# 0 to 3, in the upper two bits of the byte, the |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 |mod|
# field to 3 and the |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 |BITS 16| with no |67| prefix, or
# |BITS 32| with a |67| prefix), the SIB byte is never used. The general
# rules for |mod| and |r/m| (there is an exception, given below) are:

#     * The |mod| field gives the length of the displacement field: 0
#       means no displacement, 1 means one byte, and 2 means two bytes.
#     * The |r/m| field encodes the combination of registers to be added
#       to the displacement to give the accessed address: 0 means |BX+SI|,
#       1 means |BX+DI|, 2 means |BP+SI|, 3 means |BP+DI|, 4 means |SI|
#       only, 5 means |DI| only, 6 means |BP| only, and 7 means |BX| only.

# However, there is a special case:

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

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

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

#     * The |mod| field gives the length of the displacement field: 0
#       means no displacement, 1 means one byte, and 2 means four bytes.
#     * If only one register is to be added to the displacement, and it is
#       not |ESP|, the |r/m| field gives its register value, and the SIB
#       byte is absent. If the |r/m| field is 4 (which would encode
#       |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 |scale| field, in the top two bits, the |index|
# field in the next three, and the |base| field in the bottom three. The
# general rules are:

#     * The |base| field encodes the register value of the base register.
#     * The |index| field encodes the register value of the index
#       register, unless it is 4, in which case no index register is used
#       (so |ESP| cannot be used as an index register).
#     * The |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:

#     * If |mod| is 0 and |r/m| is 5, the effective address encoded is not
#       |[EBP]| as the above rules would suggest, but instead |[disp32]|:
#       the displacement field is present and is four bytes long, and no
#       registers are added to the displacement.
#     * If |mod| is 0, |r/m| is 4 (meaning the SIB byte is present) and
#       |base| is 4, the effective address encoded is not |[EBP+index]| as
#       the above rules would suggest, but instead |[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).


#       A.3 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:

#     * |8086|, |186|, |286|, |386|, |486|, |PENT| and |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.
#     * |CYRIX| indicates that the instruction is specific to Cyrix
#       processors, for example the extra MMX instructions in the Cyrix
#       extended MMX instruction set.
#     * |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).
#     * |MMX| indicates that the instruction is an MMX one, and will run
#       on MMX-capable Pentium processors and the Pentium II.
#     * |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.
#     * |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.


#       A.4 |AAA|, |AAS|, |AAM|, |AAD|: ASCII Adjustments

# AAA                           ; 37                   [8086]

# AAS                           ; 3F                   [8086]

# AAD                           ; D5 0A                [8086]
# AAD imm                       ; D5 ib                [8086]

# AAM                           ; D4 0A                [8086]
# 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 /unpacked/ (one BCD digit per byte - easy to translate to
# and from ASCII, hence the instruction names) form. There are also packed
# BCD instructions |DAA| and |DAS|: see section A.23 <#section-A.23>.

# |AAA| should be used after a one-byte |ADD| instruction whose
# destination was the |AL| register: by means of examining the value in
# the low nibble of |AL| and also the auxiliary carry flag |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
# |ADD|/|AAA| on the low digits, then doing |ADC|/|AAA| on each subsequent
# digit.

# |AAS| works similarly to |AAA|, but is for use after |SUB| instructions
# rather than |ADD|.

# |AAM| is for use after you have multiplied two decimal digits together
# and left the result in |AL|: it divides |AL| by ten and stores the
# quotient in |AH|, leaving the remainder in |AL|. The divisor 10 can be
# changed by specifying an operand to the instruction: a particularly
# handy use of this is |AAM 16|, causing the two nibbles in |AL| to be
# separated into |AH| and |AL|.

# |AAD| performs the inverse operation to |AAM|: it multiplies |AH| by
# ten, adds it to |AL|, and sets |AH| to zero. Again, the multiplier 10
# can be changed.


#       A.5 |ADC|: Add with Carry

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

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

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

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

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

# |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 flags are set according to the result of the
# operation: in particular, the carry flag is affected and can be used by
# a subsequent |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
# |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 |ADD| (section A.6 <#section-A.6>).


#       A.6 |ADD|: Add Integers

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

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

# ADD r/m8,imm8                 ; 80 /0 ib             [8086]
# ADD r/m16,imm16               ; o16 81 /0 iw         [8086]
# ADD r/m32,imm32               ; o32 81 /0 id         [386]

# ADD r/m16,imm8                ; o16 83 /0 ib         [8086]
# ADD r/m32,imm8                ; o32 83 /0 ib         [386]

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

# |ADD| performs integer addition: it adds its two operands together, 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 |ADC| instruction (section
# A.5 <#section-A.5>).

# 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
# |BYTE| qualifier is necessary to force NASM to generate this form of the
# instruction.


#       A.7 |AND|: Bitwise AND

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

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

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

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

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

# |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.

# 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
# |BYTE| qualifier is necessary to force NASM to generate this form of the
# instruction.

# The MMX instruction |PAND| (see section A.116 <#section-A.116>) performs
# the same operation on the 64-bit MMX registers.


#       A.8 |ARPL|: Adjust RPL Field of Selector

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

# |ARPL| expects its two word operands to be segment selectors. It adjusts
# the 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 RPL field of the source
# operand. The zero flag is set if and only if a change had to be made.


#       A.9 |BOUND|: Check Array Index against Bounds

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

# |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 BR exception.
# Otherwise, it does nothing.


#       A.10 |BSF|, |BSR|: Bit Scan

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

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

# |BSF| searches for a set bit in its source (second) operand, starting
# from the bottom, 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.

# |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).


#       A.11 |BSWAP|: Byte Swap

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

# |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 |AX|, |BX|, |CX| or
# |DX|, |XCHG| can be used.


#       A.12 |BT|, |BTC|, |BTR|, |BTS|: Bit Test

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

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

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

# BTS r/m16,reg16               ; o16 0F AB /r         [386]
# BTS r/m32,reg32               ; o32 0F AB /r         [386]
# BTS r/m16,imm                 ; o16 0F BA /5 ib      [386]
# 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, |BTR| also resets (clears) the bit in the operand itself. |BTS|
# sets the bit, and |BTC| complements the bit. |BT| does not modify its
# operands.

# The bit offset should be no greater than the size of the operand.


#       A.13 |CALL|: Call Subroutine

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

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

# |CS| is pushed as well as |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
# |CALL FAR mem| forms.

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

# The |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 |CALL WORD FAR mem| or |CALL DWORD
# FAR mem|.

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

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

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


#       A.14 |CBW|, |CWD|, |CDQ|, |CWDE|: Sign Extensions

# CBW                           ; o16 98               [8086]
# CWD                           ; o16 99               [8086]
# CDQ                           ; o32 99               [386]
# CWDE                          ; o32 98               [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.

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


#       A.15 |CLC|, |CLD|, |CLI|, |CLTS|: Clear Flags

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

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

# To set the carry, direction, or interrupt flags, use the |STC|, |STD|
# and |STI| instructions (section A.156 <#section-A.156>). To invert the
# carry flag, use |CMC| (section A.16 <#section-A.16>).


#       A.16 |CMC|: Complement Carry Flag

# CMC                           ; F5                   [8086]

# |CMC| changes the value of the carry flag: if it was 0, it sets it to 1,
# and vice versa.


#       A.17 |CMOVcc|: Conditional Move

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

# |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 section A.2.2 <#section-A.2.2>.

# Although the |CMOV| instructions are flagged |P6| above, they may not be
# supported by all Pentium Pro processors; the |CPUID| instruction
# (section A.22 <#section-A.22>) will return a bit which indicates whether
# conditional moves are supported.


#       A.18 |CMP|: Compare Integers

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

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

# CMP r/m8,imm8                 ; 80 /0 ib             [8086]
# CMP r/m16,imm16               ; o16 81 /0 iw         [8086]
# CMP r/m32,imm32               ; o32 81 /0 id         [386]

# DEADCMP r/m16,imm8                ; o16 83 /0 ib         [8086]
# DEADCMP r/m32,imm8                ; o32 83 /0 ib         [386]

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

# |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
# |BYTE| qualifier is necessary to force NASM to generate this form of the
# instruction.


#       A.19 |CMPSB|, |CMPSW|, |CMPSD|: Compare Strings

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

# |CMPSB| compares the byte at |[DS:SI]| or |[DS:ESI]| with the byte at
# |[ES:DI]| or |[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) |SI| and |DI| (or |ESI| and
# |EDI|).

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

# The segment register used to load from |[SI]| or |[ESI]| can be
# overridden by using a segment register name as a prefix (for example,
# |es cmpsb|). The use of |ES| for the load from |[DI]| or |[EDI]| cannot
# be overridden.

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


#       A.20 |CMPXCHG|, |CMPXCHG486|: Compare and Exchange

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

# CMPXCHG486 r/m8,reg8          ; 0F A6 /r             [486,UNDOC]
# CMPXCHG486 r/m16,reg16        ; o16 0F A7 /r         [486,UNDOC]
# 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 |CMPXCHG486| form to generate
# the non-standard opcode.

# |CMPXCHG| compares its destination (first) operand to the value in |AL|,
# |AX| or |EAX| (depending on the 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 leaves the
# destination alone.

# |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 |EAX|, load the
# updated value into |EBX|, and then execute the instruction |lock cmpxchg
# [value],ebx|. If |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 |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.


#       A.21 |CMPXCHG8B|: Compare and Exchange Eight Bytes

# CMPXCHG8B mem                 ; 0F C7 /1             [PENT]

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


#       A.22 |CPUID|: Get CPU Identification Code

# CPUID                         ; 0F A2                [PENT]

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

# |CPUID| also acts as a barrier to serialise instruction execution:
# executing the |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:

#     * If |EAX| is zero on input, |EAX| on output holds the maximum
#       acceptable input value of |EAX|, and |EBX:EDX:ECX| contain the
#       string |"GenuineIntel"| (or not, if you have a clone processor).
#       That is to say, |EBX| contains |"Genu"| (in NASM's own sense of
#       character constants, described in section 3.4.2
#       <nasmdoc3.html#section-3.4.2>), |EDX| contains |"ineI"| and |ECX|
#       contains |"ntel"|.
#     * If |EAX| is one on input, |EAX| on output contains version
#       information about the processor, and |EDX| contains a set of
#       feature flags, showing the presence and absence of various
#       features. For example, bit 8 is set if the |CMPXCHG8B| instruction
#       (section A.21 <#section-A.21>) is supported, bit 15 is set if the
#       conditional move instructions (section A.17 <#section-A.17> and
#       section A.34 <#section-A.34>) are supported, and bit 23 is set if
#       MMX instructions are supported.
#     * If |EAX| is two on input, |EAX|, |EBX|, |ECX| and |EDX| all
#       contain information about caches and TLBs (Translation Lookahead
#       Buffers).

# For more information on the data returned from |CPUID|, see the
# documentation on Intel's web site.


#       A.23 |DAA|, |DAS|: Decimal Adjustments

# DAA                           ; 27                   [8086]
# DAS                           ; 2F                   [8086]

# These instructions are used in conjunction with the add and subtract
# instructions to perform binary-coded decimal arithmetic in /packed/ (one
# BCD digit per nibble) form. For the unpacked equivalents, see section
# A.4 <#section-A.4>.

# |DAA| should be used after a one-byte |ADD| instruction whose
# destination was the |AL| register: by means of examining the value in
# the |AL| and also the auxiliary carry flag |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 |ADD|/|DAA| on the low two digits, then doing
# |ADC|/|DAA| on each subsequent pair of digits.

# |DAS| works similarly to |DAA|, but is for use after |SUB| instructions
# rather than |ADD|.


#       A.24 |DEC|: Decrement Integer

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

# |DEC| subtracts 1 from its operand. It does /not/ affect the carry flag:
# to affect the carry flag, use |SUB something,1| (see section A.159
# <#section-A.159>). See also |INC| (section A.79 <#section-A.79>).


#       A.25 |DIV|: Unsigned Integer Divide

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

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

#     * For |DIV r/m8|, |AX| is divided by the given operand; the quotient
#       is stored in |AL| and the remainder in |AH|.
#     * For |DIV r/m16|, |DX:AX| is divided by the given operand; the
#       quotient is stored in |AX| and the remainder in |DX|.
#     * For |DIV r/m32|, |EDX:EAX| is divided by the given operand; the
#       quotient is stored in |EAX| and the remainder in |EDX|.

# Signed integer division is performed by the |IDIV| instruction: see
# section A.76 <#section-A.76>.


#       A.26 |EMMS|: Empty MMX State

# MMS                          ; 0F 77                [PENT,MMX]

# |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 MMX instructions and before
# executing any subsequent floating-point operations.


#       A.27 |ENTER|: Create Stack Frame

# ENTER imm,imm                 ; C8 iw ib             [186]

# |ENTER| constructs a stack frame for a high-level language procedure
# call. The first operand (the |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 |ib| above) gives the nesting level of
# the procedure (for languages like Pascal, with nested procedures).

# The function of |ENTER|, with a nesting level of zero, is equivalent to

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

# This creates a stack frame with the procedure parameters accessible
# upwards from |EBP|, and local variables accessible downwards from |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 |EBP| is accessible in
# memory at |[EBP-4]|.

# This allows |ENTER|, when called with a nesting level of two, to look at
# the stack frame described by the /previous/ value of |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, |[EBP-4]| holds the frame pointer of the most
# recent level-one procedure call and |[EBP-8]| holds that of the most
# recent level-two call. And so on, for nesting levels up to 31.

# Stack frames created by |ENTER| can be destroyed by the |LEAVE|
# instruction: see section A.94 <#section-A.94>.


#       A.28 |F2XM1|: Calculate 2**X-1

# F2XM1                         ; D9 F0                [8086,FPU]

# |F2XM1| raises 2 to the power of |ST0|, subtracts one, and stores the
# result back into |ST0|. The initial contents of |ST0| must be a number
# in the range -1 to +1.


#       A.29 |FABS|: Floating-Point Absolute Value

# FABS                          ; D9 E1                [8086,FPU]

# |FABS| computes the absolute value of |ST0|, storing the result back in
# |ST0|.


#       A.30 |FADD|, |FADDP|: Floating-Point Addition

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

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

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

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

# |FADD|, given one operand, adds the operand to |ST0| and stores the
# result back in |ST0|. If the operand has the |TO| modifier, the result
# is stored in the register given rather than in |ST0|.

# |FADDP| performs the same function as |FADD TO|, but pops the register
# stack after storing the result.

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


#       A.31 |FBLD|, |FBSTP|: BCD Floating-Point Load and Store

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

# |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. |FBSTP| stores the value of |ST0|, in packed BCD, at
# the given address and then pops the register stack.


#       A.32 |FCHS|: Floating-Point Change Sign

# FCHS                          ; D9 E0                [8086,FPU]

# |FCHS| negates the number in |ST0|: negative numbers become positive,
# and vice versa.


#       A.33 |FCLEX|, {FNCLEX}: Clear Floating-Point Exceptions

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

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


#       A.34 |FCMOVcc|: Floating-Point Conditional Move

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

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

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

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

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

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

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

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

# The |FCMOV| instructions perform conditional move operations: each of
# them moves the contents of the given register into |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 |B|, |BE|, |NB|,
# |NBE|, |E| and |NE| are exactly as normal, but none of the other
# standard ones are supported. Instead, the condition |U| and its
# counterpart |NU| are provided; the |U| condition is satisfied if the
# last two floating-point numbers compared were /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 |U| condition is notionally
# equivalent to |PE|, and |NU| is equivalent to |PO|.)

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

# Although the |FCMOV| instructions are flagged |P6| above, they may not
# be supported by all Pentium Pro processors; the |CPUID| instruction
# (section A.22 <#section-A.22>) will return a bit which indicates whether
# conditional moves are supported.


#       A.35 |FCOM|, |FCOMP|, |FCOMPP|, |FCOMI|, |FCOMIP|: Floating-Point
#       Compare

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

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

# FCOMPP                        ; DE D9                [8086,FPU]

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

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

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

# |FCOMP| does the same as |FCOM|, but pops the register stack afterwards.
# |FCOMPP| compares |ST0| with |ST1| and then pops the register stack twice.

# |FCOMI| and |FCOMIP| work like the corresponding forms of |FCOM| and
# |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 |FCOM| instructions differ from the |FUCOM| instructions (section
# A.69 <#section-A.69>) only in the way they handle quiet NaNs: |FUCOM|
# will handle them silently and set the condition code flags to an
# `unordered' result, whereas |FCOM| will generate an exception.


#       A.36 |FCOS|: Cosine

# FCOS                          ; D9 FF                [386,FPU]

# |FCOS| computes the cosine of |ST0| (in radians), and stores the result
# in |ST0|. See also |FSINCOS| (section A.61 <#section-A.61>).


#       A.37 |FDECSTP|: Decrement Floating-Point Stack Pointer

# FDECSTP                       ; D9 F6                [8086,FPU]

# |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 |ST7| had been pushed on the stack. See also |FINCSTP|
# (section A.46 <#section-A.46>).


#       A.38 |FxDISI|, |FxENI|: Disable and Enable Floating-Point Interrupts

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

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

# |FDISI| and |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.

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


#       A.39 |FDIV|, |FDIVP|, |FDIVR|, |FDIVRP|: Floating-Point Division

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

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

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

# FDIVR mem32                   ; D8 /0                [8086,FPU]
# FDIVR mem64                   ; DC /0                [8086,FPU]

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

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

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

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

# |FDIV| divides |ST0| by the given operand and stores the result back in
# |ST0|, unless the |TO| qualifier is given, in which case it divides the
# given operand by |ST0| and stores the result in the operand.

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

# |FDIVP| operates like |FDIV TO|, but pops the register stack once it has
# finished. |FDIVRP| operates like |FDIVR TO|, but pops the register stack
# once it has finished.


#       A.40 |FFREE|: Flag Floating-Point Register as Unused

# FFREE fpureg                  ; DD C0+r              [8086,FPU]

# |FFREE| marks the given register as being empty.


#       A.41 |FIADD|: Floating-Point/Integer Addition

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

# |FIADD| adds the 16-bit or 32-bit integer stored in the given memory
# location to |ST0|, storing the result in |ST0|.


#       A.42 |FICOM|, |FICOMP|: Floating-Point/Integer Compare

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

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

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


#       A.43 |FIDIV|, |FIDIVR|: Floating-Point/Integer Division

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

# FIDIVR mem16                  ; DE /0                [8086,FPU]
# FIDIVR mem32                  ; DA /0                [8086,FPU]

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


#       A.44 |FILD|, |FIST|, |FISTP|: Floating-Point/Integer Conversion

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

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

# FISTP mem16                   ; DF /3                [8086,FPU]
# FISTP mem32                   ; DB /3                [8086,FPU]
# FISTP mem64                   ; DF /0                [8086,FPU]

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


#       A.45 |FIMUL|: Floating-Point/Integer Multiplication

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

# |FIMUL| multiplies |ST0| by the 16-bit or 32-bit integer stored in the
# given memory location, and stores the result in |ST0|.


#       A.46 |FINCSTP|: Increment Floating-Point Stack Pointer

# FINCSTP                       ; D9 F7                [8086,FPU]

# |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 |ST7|
# (previously |ST0|) as empty. See also |FDECSTP| (section A.37
# <#section-A.37>).


#       A.47 |FINIT|, |FNINIT|: Initialise Floating-Point Unit

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

# |FINIT| initialises the FPU to its default state. It flags all registers
# as empty, though it does not actually change their values. |FNINIT| does
# the same, without first waiting for pending exceptions to clear.


#       A.48 |FISUB|: Floating-Point/Integer Subtraction

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

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

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


#       A.49 |FLD|: Floating-Point Load

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

# |FLD| loads a floating-point value out of the given register or memory
# location, and pushes it on the FPU register stack.


#       A.50 |FLDxx|: Floating-Point Load Constants

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

# These instructions push specific standard constants on the FPU register
# stack. |FLD1| pushes the value 1; |FLDL2E| pushes the base-2 logarithm
# of e; |FLDL2T| pushes the base-2 log of 10; |FLDLG2| pushes the base-10
# log of 2; |FLDLN2| pushes the base-e log of 2; |FLDPI| pushes pi; and
# |FLDZ| pushes zero.


#       A.51 |FLDCW|: Load Floating-Point Control Word

# FLDCW mem16                   ; D9 /5                [8086,FPU]

# |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 |FSTCW| (section A.64 <#section-A.64>).


#       A.52 |FLDENV|: Load Floating-Point Environment

# FLDENV mem                    ; D9 /4                [8086,FPU]

# |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 |FSTENV| (section A.65 <#section-A.65>).


#       A.53 |FMUL|, |FMULP|: Floating-Point Multiply

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

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

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

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

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


#       A.54 |FNOP|: Floating-Point No Operation

# FNOP                          ; D9 D0                [8086,FPU]

# |FNOP| does nothing.


#       A.55 |FPATAN|, |FPTAN|: Arctangent and Tangent

# FPATAN                        ; D9 F3                [8086,FPU]
# FPTAN                         ; D9 F2                [8086,FPU]

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

# |FPTAN| computes the tangent of the value in |ST0| (in radians), and
# stores the result back into |ST0|.


#       A.56 |FPREM|, |FPREM1|: Floating-Point Partial Remainder

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

# These instructions both produce the remainder obtained by dividing |ST0|
# by |ST1|. This is calculated, notionally, by dividing |ST0| by |ST1|,
# rounding the result to an integer, multiplying by |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 |ST0|.

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

# Both instructions calculate /partial/ remainders, meaning that they may
# not manage to provide the final result, but might leave intermediate
# results in |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 |FPREM| or |FPREM1| until C2 becomes clear.


#       A.57 |FRNDINT|: Floating-Point Round to Integer

# FRNDINT                       ; D9 FC                [8086,FPU]

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


#       A.58 |FSAVE|, |FRSTOR|: Save/Restore Floating-Point State

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

# FRSTOR mem                    ; DD /4                [8086,FPU]

# |FSAVE| saves the entire floating-point unit state, including all the
# information saved by |FSTENV| (section A.65 <#section-A.65>) plus the
# contents of all the registers, to a 94 or 108 byte area of memory
# (depending on the CPU mode). |FRSTOR| restores the floating-point state
# from the same area of memory.

# |FNSAVE| does the same as |FSAVE|, without first waiting for pending
# floating-point exceptions to clear.


#       A.59 |FSCALE|: Scale Floating-Point Value by Power of Two

# FSCALE                        ; D9 FD                [8086,FPU]

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


#       A.60 |FSETPM|: Set Protected Mode

# FSETPM                        ; DB E4                [286,FPU]

# This instruction initalises 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.


#       A.61 |FSIN|, |FSINCOS|: Sine and Cosine

# FSIN                          ; D9 FE                [386,FPU]
# FSINCOS                       ; D9 FB                [386,FPU]

# |FSIN| calculates the sine of |ST0| (in radians) and stores the result
# in |ST0|. |FSINCOS| does the same, but then pushes the cosine of the
# same value on the register stack, so that the sine ends up in |ST1| and
# the cosine in |ST0|. |FSINCOS| is faster than executing |FSIN| and
# |FCOS| (see section A.36 <#section-A.36>) in succession.


#       A.62 |FSQRT|: Floating-Point Square Root

# FSQRT                         ; D9 FA                [8086,FPU]

# |FSQRT| calculates the square root of |ST0| and stores the result in |ST0|.


#       A.63 |FST|, |FSTP|: Floating-Point Store

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

# FSTP mem32                    ; D9 /3                [8086,FPU]
# FSTP mem64                    ; DD /3                [8086,FPU]
# FSTP mem80                    ; DB /0                [8086,FPU]
# FSTP fpureg                   ; DD D8+r              [8086,FPU]

# |FST| stores the value in |ST0| into the given memory location or other
# FPU register. |FSTP| does the same, but then pops the register stack.


#       A.64 |FSTCW|: Store Floating-Point Control Word

# FSTCW mem16                   ; 9B D9 /0             [8086,FPU]
# FNSTCW mem16                  ; D9 /0                [8086,FPU]

# |FSTCW| stores the FPU control word (governing things like the rounding
# mode, the precision, and the exception masks) into a 2-byte memory area.
# See also |FLDCW| (section A.51 <#section-A.51>).

# |FNSTCW| does the same thing as |FSTCW|, without first waiting for
# pending floating-point exceptions to clear.


#       A.65 |FSTENV|: Store Floating-Point Environment

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

# |FSTENV| stores the 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 |FLDENV| (section A.52 <#section-A.52>).

# |FNSTENV| does the same thing as |FSTENV|, without first waiting for
# pending floating-point exceptions to clear.


#       A.66 |FSTSW|: Store Floating-Point Status Word

# FSTSW mem16                   ; 9B DD /0             [8086,FPU]
# FSTSW AX                      ; 9B DF E0             [286,FPU]

# FNSTSW mem16                  ; DD /0                [8086,FPU]
# FNSTSW AX                     ; DF E0                [286,FPU]

# |FSTSW| stores the FPU status word into |AX| or into a 2-byte memory area.

# |FNSTSW| does the same thing as |FSTSW|, without first waiting for
# pending floating-point exceptions to clear.


#       A.67 |FSUB|, |FSUBP|, |FSUBR|, |FSUBRP|: Floating-Point Subtract

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

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

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

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

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

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

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

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

# |FSUB| subtracts the given operand from |ST0| and stores the result back
# in |ST0|, unless the |TO| qualifier is given, in which case it subtracts
# |ST0| from the given operand and stores the result in the operand.

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

# |FSUBP| operates like |FSUB TO|, but pops the register stack once it has
# finished. |FSUBRP| operates like |FSUBR TO|, but pops the register stack
# once it has finished.


#       A.68 |FTST|: Test |ST0| Against Zero

# FTST                          ; D9 E4                [8086,FPU]

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


#       A.69 |FUCOMxx|: Floating-Point Unordered Compare

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

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

# FUCOMPP                       ; DA E9                [386,FPU]

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

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

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

# |FUCOMP| does the same as |FUCOM|, but pops the register stack
# afterwards. |FUCOMPP| compares |ST0| with |ST1| and then pops the
# register stack twice.

# |FUCOMI| and |FUCOMIP| work like the corresponding forms of |FUCOM| and
# |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 |FUCOM| instructions differ from the |FCOM| instructions (section
# A.35 <#section-A.35>) only in the way they handle quiet NaNs: |FUCOM|
# will handle them silently and set the condition code flags to an
# `unordered' result, whereas |FCOM| will generate an exception.


#       A.70 |FXAM|: Examine Class of Value in |ST0|

# FXAM                          ; D9 E5                [8086,FPU]

# |FXAM| sets the FPU flags C3, C2 and C0 depending on the type of value
# stored in |ST0|: 000 (respectively) for an unsupported format, 001 for a
# NaN, 010 for a normal finite number, 011 for an infinity, 100 for a
# zero, 101 for an empty register, and 110 for a denormal. It also sets
# the C1 flag to the sign of the number.


#       A.71 |FXCH|: Floating-Point Exchange

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

# |FXCH| exchanges |ST0| with a given FPU register. The no-operand form
# exchanges |ST0| with |ST1|.


#       A.72 |FXTRACT|: Extract Exponent and Significand

# FXTRACT                       ; D9 F4                [8086,FPU]

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


#       A.73 |FYL2X|, |FYL2XP1|: Compute Y times Log2(X) or Log2(X+1)

# FYL2X                         ; D9 F1                [8086,FPU]
# FYL2XP1                       ; D9 F9                [8086,FPU]

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

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


#       A.74 |HLT|: Halt Processor

# HLT                           ; F4                   [8086]

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


#       A.75 |IBTS|: Insert Bit String

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

# No clear documentation seems to be available for this instruction: the
# best I've been able to find reads `Takes a string of bits from the
# second operand and puts them in the first operand'. It is present only
# in early 386 processors, and conflicts with the opcodes for
# |CMPXCHG486|. NASM supports it only for completeness. Its counterpart is
# |XBTS| (see section A.167 <#section-A.167>).


#       A.76 |IDIV|: Signed Integer Divide

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

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

#     * For |IDIV r/m8|, |AX| is divided by the given operand; the
#       quotient is stored in |AL| and the remainder in |AH|.
#     * For |IDIV r/m16|, |DX:AX| is divided by the given operand; the
#       quotient is stored in |AX| and the remainder in |DX|.
#     * For |IDIV r/m32|, |EDX:EAX| is divided by the given operand; the
#       quotient is stored in |EAX| and the remainder in |EDX|.

# Unsigned integer division is performed by the |DIV| instruction: see
# section A.25 <#section-A.25>.


#       A.77 |IMUL|: Signed Integer Multiply

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

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

# IMUL reg16,imm8               ; o16 6B /r ib         [286]
# IMUL reg16,imm16              ; o16 69 /r iw         [286]
# IMUL reg32,imm8               ; o32 6B /r ib         [386]
# IMUL reg32,imm32              ; o32 69 /r id         [386]

# IMUL reg16,r/m16,imm8         ; o16 6B /r ib         [286]
# IMUL reg16,r/m16,imm16        ; o16 69 /r iw         [286]
# IMUL reg32,r/m32,imm8         ; o32 6B /r ib         [386]
# IMUL reg32,r/m32,imm32        ; o32 69 /r id         [386]

# |IMUL| performs signed integer multiplication. For the single-operand
# form, the other operand and destination are implicit, in the following way:

#     * For |IMUL r/m8|, |AL| is multiplied by the given operand; the
#       product is stored in |AX|.
#     * For |IMUL r/m16|, |AX| is multiplied by the given operand; the
#       product is stored in |DX:AX|.
#     * For |IMUL r/m32|, |EAX| is multiplied by the given operand; the
#       product is stored in |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 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 |/r| takes both its register and |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 |BYTE| qualifier is necessary to force NASM to generate this form of
# the instruction.

# Unsigned integer multiplication is performed by the |MUL| instruction:
# see section A.107 <#section-A.107>.


#       A.78 |IN|: Input from I/O Port

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

# |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 |DX|. See also |OUT| (section A.111
# <#section-A.111>).


#       A.79 |INC|: Increment Integer

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

# |INC| adds 1 to its operand. It does /not/ affect the carry flag: to
# affect the carry flag, use |ADD something,1| (see section A.6
# <#section-A.6>). See also |DEC| (section A.24 <#section-A.24>).


#       A.80 |INSB|, |INSW|, |INSD|: Input String from I/O Port

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

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

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

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

# |INSW| and |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 |REP| prefix may be used to repeat the instruction |CX| (or |ECX| -
# again, the address size chooses which) times.

# See also |OUTSB|, |OUTSW| and |OUTSD| (section A.112 <#section-A.112>).


#       A.81 |INT|: Software Interrupt

# INT imm8                      ; CD ib                [8086]

# |INT| causes a software interrupt through a specified vector number from
# 0 to 255.

# The code generated by the |INT| instruction is always two bytes long:
# although there are short forms for some |INT| instructions, NASM does
# not generate them when it sees the |INT| mnemonic. In order to generate
# single-byte breakpoint instructions, use the |INT3| or |INT1|
# instructions (see section A.82 <#section-A.82>) instead.


#       A.82 |INT3|, |INT1|, |ICEBP|, |INT01|: Breakpoints

# INT1                          ; F1                   [P6]
# ICEBP                         ; F1                   [P6]
# INT01                         ; F1                   [P6]

# INT3                          ; CC                   [8086]

# |INT1| and |INT3| are short one-byte forms of the instructions |INT 1|
# and |INT 3| (see section A.81 <#section-A.81>). They perform a similar
# function to their longer counterparts, but take up less code space. They
# are used as breakpoints by debuggers.

# |INT1|, and its alternative synonyms |INT01| and |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. |INT3| is the instruction normally used
# as a breakpoint by debuggers.

# |INT3| is not precisely equivalent to |INT 3|: the short form, since it
# is designed to be used as a breakpoint, bypasses the normal IOPL checks
# in virtual-8086 mode, and also does not go through interrupt redirection.


#       A.83 |INTO|: Interrupt if Overflow

# INTO                          ; CE                   [8086]

# |INTO| performs an |INT 4| software interrupt (see section A.81
# <#section-A.81>) if and only if the overflow flag is set.


#       A.84 |INVD|: Invalidate Internal Caches

# INVD                          ; 0F 08                [486]

# |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
# |WBINVD| (section A.164 <#section-A.164>).


#       A.85 |INVLPG|: Invalidate TLB Entry

# INVLPG mem                    ; 0F 01 /0             [486]

# |INVLPG| invalidates the translation lookahead buffer (TLB) entry
# associated with the supplied memory address.


#       A.86 |IRET|, |IRETW|, |IRETD|: Return from Interrupt

# IRET                          ; CF                   [8086]
# IRETW                         ; o16 CF               [8086]
# IRETD                         ; o32 CF               [386]

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

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

# |IRET| is a shorthand for either |IRETW| or |IRETD|, depending on the
# default |BITS| setting at the time.


#       A.87 |JCXZ|, |JECXZ|: Jump if CX/ECX Zero

# JCXZ imm                      ; o16 E3 rb            [8086]
# JECXZ imm                     ; o32 E3 rb            [386]

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


#       A.88 |JMP|: Jump

# JMP imm                       ; E9 rw/rd             [8086]

# JMP SHORT imm                 ; EB rb                [8086]
# JMP imm:imm16                 ; o16 EA iw iw         [8086]
# JMP imm:imm32                 ; o32 EA id iw         [386]

# JMP FAR mem                   ; o16 FF /5            [8086]
# JMP FAR mem                   ; o32 FF /5            [386]
# JMP r/m16                     ; o16 FF /4            [8086]
# JMP r/m32                     ; o32 FF /4            [386]

# |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.

# |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 |JMP SHORT| for you: you must explicitly code
# |SHORT| every time you want a short jump.

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

# The |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 |JMP WORD FAR mem| or |JMP DWORD
# FAR mem|.

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

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

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


#       A.89 |Jcc|: Conditional Branch

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

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

# The ordinary form of the instructions has only a 128-byte range; the
# |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 |Jcc NEAR|, you have to use the |NEAR| keyword.

# The |SHORT| keyword is allowed on the first form of the instruction, for
# clarity, but is not necessary.


#       A.90 |LAHF|: Load AH from Flags

# LAHF                          ; 9F                   [8086]

# |LAHF| sets the |AH| register according to the contents of the low byte
# of the flags word. See also |SAHF| (section A.145 <#section-A.145>).


#       A.91 |LAR|: Load Access Rights

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

# |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.


#       A.92 |LDS|, |LES|, |LFS|, |LGS|, |LSS|: Load Far Pointer

# LDS reg16,mem                 ; o16 C5 /r            [8086]
# LDS reg32,mem                 ; o32 C5 /r            [8086]

# LES reg16,mem                 ; o16 C4 /r            [8086]
# LES reg32,mem                 ; o32 C4 /r            [8086]

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

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

# LSS reg16,mem                 ; o16 0F B2 /r         [386]
# 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. |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 /next/
# 16 bits from memory into |DS|. |LES|, |LFS|, |LGS| and |LSS| work in the
# same way but use the other segment registers.


#       A.93 |LEA|: Load Effective Address

# LEA reg16,mem                 ; o16 8D /r            [8086]
# LEA reg32,mem                 ; o32 8D /r            [8086]

# |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. |LEA EAX,[EBX+ECX*4+100]|) in
# one instruction.

# |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.


#       A.94 |LEAVE|: Destroy Stack Frame

# LEAVE                         ; C9                   [186]

# |LEAVE| destroys a stack frame of the form created by the |ENTER|
# instruction (see section A.27 <#section-A.27>). It is functionally
# equivalent to |MOV ESP,EBP| followed by |POP EBP| (or |MOV SP,BP|
# followed by |POP BP| in 16-bit mode).


#       A.95 |LGDT|, |LIDT|, |LLDT|: Load Descriptor Tables

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

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

# |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 LDTR (local descriptor table register).

# See also |SGDT|, |SIDT| and |SLDT| (section A.151 <#section-A.151>).


#       A.96 |LMSW|: Load/Store Machine Status Word

# LMSW r/m16                    ; 0F 01 /6             [286,PRIV]

# |LMSW| loads the bottom four bits of the source operand into the bottom
# four bits of the |CR0| control register (or the Machine Status Word, on
# 286 processors). See also |SMSW| (section A.155 <#section-A.155>).


#       A.97 |LOADALL|, |LOADALL286|: Load Processor State

# LOADALL                       ; 0F 07                [386,UNDOC]
# 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 |0x800|, and on the 386
# and 486 it is at |[ES:EDI]|.


#       A.98 |LODSB|, |LODSW|, |LODSD|: Load from String

# LODSB                         ; AC                   [8086]
# LODSW                         ; o16 AD               [8086]
# LODSD                         ; o32 AD               [386]

# |LODSB| loads a byte from |[DS:SI]| or |[DS:ESI]| into |AL|. It then
# increments or decrements (depending on the direction flag: increments if
# the flag is clear, decrements if it is set) |SI| or |ESI|.

# The register used is |SI| if the address size is 16 bits, and |ESI| if
# it is 32 bits. If you need to use an address size not equal to the
# current |BITS| setting, you can use an explicit |a16| or |a32| prefix.

# The segment register used to load from |[SI]| or |[ESI]| can be
# overridden by using a segment register name as a prefix (for example,
# |es lodsb|).

# |LODSW| and |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.


#       A.99 |LOOP|, |LOOPE|, |LOOPZ|, |LOOPNE|, |LOOPNZ|: Loop with Counter

# LOOP imm                      ; E2 rb                [8086]
# LOOP imm,CX                   ; a16 E2 rb            [8086]
# LOOP imm,ECX                  ; a32 E2 rb            [386]

# LOOPE imm                     ; E1 rb                [8086]
# LOOPE imm,CX                  ; a16 E1 rb            [8086]
# LOOPE imm,ECX                 ; a32 E1 rb            [386]
# LOOPZ imm                     ; E1 rb                [8086]
# LOOPZ imm,CX                  ; a16 E1 rb            [8086]
# LOOPZ imm,ECX                 ; a32 E1 rb            [386]

# LOOPNE imm                    ; E0 rb                [8086]
# LOOPNE imm,CX                 ; a16 E0 rb            [8086]
# LOOPNE imm,ECX                ; a32 E0 rb            [386]
# LOOPNZ imm                    ; E0 rb                [8086]
# LOOPNZ imm,CX                 ; a16 E0 rb            [8086]
# LOOPNZ imm,ECX                ; a32 E0 rb            [386]

# |LOOP| decrements its counter register (either |CX| or |ECX| - if one is
# not specified explicitly, the |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.

# |LOOPE| (or its synonym |LOOPZ|) adds the additional condition that it
# only jumps if the counter is nonzero /and/ the zero flag is set.
# Similarly, |LOOPNE| (and |LOOPNZ|) jumps only if the counter is nonzero
# and the zero flag is clear.


#       A.100 |LSL|: Load Segment Limit

# LSL reg16,r/m16               ; o16 0F 03 /r         [286,PRIV]
# LSL reg32,r/m32               ; o32 0F 03 /r         [286,PRIV]

# |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 GDT or 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.


#       A.101 |LTR|: Load Task Register

# LTR r/m16                     ; 0F 00 /3             [286,PRIV]

# |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.


#       A.102 |MOV|: Move Data

# MOV r/m8,reg8                 ; 88 /r                [8086]
# MOV r/m16,reg16               ; o16 89 /r            [8086]
# MOV r/m32,reg32               ; o32 89 /r            [386]
# MOV reg8,r/m8                 ; 8A /r                [8086]
# MOV reg16,r/m16               ; o16 8B /r            [8086]
# MOV reg32,r/m32               ; o32 8B /r            [386]

# MOV reg8,imm8                 ; B0+r ib              [8086]
# MOV reg16,imm16               ; o16 B8+r iw          [8086]
# MOV reg32,imm32               ; o32 B8+r id          [386]
# MOV r/m8,imm8                 ; C6 /0 ib             [8086]
# MOV r/m16,imm16               ; o16 C7 /0 iw         [8086]
# MOV r/m32,imm32               ; o32 C7 /0 id         [386]

# MOV AL,memoffs8               ; A0 ow/od             [8086]
# MOV AX,memoffs16              ; o16 A1 ow/od         [8086]
# MOV EAX,memoffs32             ; o32 A1 ow/od         [386]
# MOV memoffs8,AL               ; A2 ow/od             [8086]
# MOV memoffs16,AX              ; o16 A3 ow/od         [8086]
# MOV memoffs32,EAX             ; o32 A3 ow/od         [386]

# MOV r/m16,segreg              ; o16 8C /r            [8086]
# MOV r/m32,segreg              ; o32 8C /r            [386]
# MOV segreg,r/m16              ; o16 8E /r            [8086]
# MOV segreg,r/m32              ; o32 8E /r            [386]

# MOV reg32,CR0/2/3/4           ; 0F 20 /r             [386]
# MOV reg32,DR0/1/2/3/6/7       ; 0F 21 /r             [386]
# MOV reg32,TR3/4/5/6/7         ; 0F 24 /r             [386]
# MOV CR0/2/3/4,reg32           ; 0F 22 /r             [386]
# MOV DR0/1/2/3/6/7,reg32       ; 0F 23 /r             [386]
# MOV TR3/4/5/6/7,reg32         ; 0F 26 /r             [386]

# |MOV| copies the contents of its source (second) operand into its
# destination (first) operand.

# In all forms of the |MOV| instruction, the two operands are the same
# size, except for moving between a segment register and an |r/m32|
# operand. These instructions are treated exactly like the corresponding
# 16-bit equivalent (so that, for example, |MOV DS,EAX| functions
# identically to |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.

# |MOV| may not use |CS| as a destination.

# |CR4| is only a supported register on the Pentium and above.


#       A.103 |MOVD|: Move Doubleword to/from MMX Register

# MOVD mmxreg,r/m32             ; 0F 6E /r             [PENT,MMX]
# MOVD r/m32,mmxreg             ; 0F 7E /r             [PENT,MMX]

# |MOVD| copies 32 bits from its source (second) operand into its
# destination (first) operand. When the destination is a 64-bit MMX
# register, the top 32 bits are set to zero.


#       A.104 |MOVQ|: Move Quadword to/from MMX Register

# MOVQ mmxreg,r/m64             ; 0F 6F /r             [PENT,MMX]
# MOVQ r/m64,mmxreg             ; 0F 7F /r             [PENT,MMX]

# |MOVQ| copies 64 bits from its source (second) operand into its
# destination (first) operand.


#       A.105 |MOVSB|, |MOVSW|, |MOVSD|: Move String

# MOVSB                         ; A4                   [8086]
# MOVSW                         ; o16 A5               [8086]
# MOVSD                         ; o32 A5               [386]

# |MOVSB| copies the byte at |[ES:DI]| or |[ES:EDI]| to |[DS:SI]| or
# |[DS:ESI]|. It then increments or decrements (depending on the direction
# flag: increments if the flag is clear, decrements if it is set) |SI| and
# |DI| (or |ESI| and |EDI|).

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

# The segment register used to load from |[SI]| or |[ESI]| can be
# overridden by using a segment register name as a prefix (for example,
# |es movsb|). The use of |ES| for the store to |[DI]| or |[EDI]| cannot
# be overridden.

# |MOVSW| and |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 |REP| prefix may be used to repeat the instruction |CX| (or |ECX| -
# again, the address size chooses which) times.


#       A.106 |MOVSX|, |MOVZX|: Move Data with Sign or Zero Extend

# MOVSX reg16,r/m8              ; o16 0F BE /r         [386]
# MOVSX reg32,r/m8              ; o32 0F BE /r         [386]
# MOVSX reg32,r/m16             ; o32 0F BF /r         [386]

# MOVZX reg16,r/m8              ; o16 0F B6 /r         [386]
# MOVZX reg32,r/m8              ; o32 0F B6 /r         [386]
# MOVZX reg32,r/m16             ; o32 0F B7 /r         [386]

# |MOVSX| sign-extends its source (second) operand to the length of its
# destination (first) operand, and copies the result into the destination
# operand. |MOVZX| does the same, but zero-extends rather than
# sign-extending.


#       A.107 |MUL|: Unsigned Integer Multiply

# MUL r/m8                      ; F6 /4                [8086]
# MUL r/m16                     ; o16 F7 /4            [8086]
# MUL r/m32                     ; o32 F7 /4            [386]

# |MUL| performs unsigned integer multiplication. The other operand to the
# multiplication, and the destination operand, are implicit, in the
# following way:

#     * For |MUL r/m8|, |AL| is multiplied by the given operand; the
#       product is stored in |AX|.
#     * For |MUL r/m16|, |AX| is multiplied by the given operand; the
#       product is stored in |DX:AX|.
#     * For |MUL r/m32|, |EAX| is multiplied by the given operand; the
#       product is stored in |EDX:EAX|.

# Signed integer multiplication is performed by the |IMUL| instruction:
# see section A.77 <#section-A.77>.


#       A.108 |NEG|, |NOT|: Two's and One's Complement

# NEG r/m8                      ; F6 /3                [8086]
# NEG r/m16                     ; o16 F7 /3            [8086]
# NEG r/m32                     ; o32 F7 /3            [386]

# NOT r/m8                      ; F6 /2                [8086]
# NOT r/m16                     ; o16 F7 /2            [8086]
# NOT r/m32                     ; o32 F7 /2            [386]

# |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.
# |NOT|, similarly, performs one's complement (inverts all the bits).


#       A.109 |NOP|: No Operation

# NOP                           ; 90                   [8086]

# |NOP| performs no operation. Its opcode is the same as that generated by
# |XCHG AX,AX| or |XCHG EAX,EAX| (depending on the processor mode; see
# section A.168 <#section-A.168>).


#       A.110 |OR|: Bitwise OR

# OR r/m8,reg8                  ; 08 /r                [8086]
# OR r/m16,reg16                ; o16 09 /r            [8086]
# OR r/m32,reg32                ; o32 09 /r            [386]

# OR reg8,r/m8                  ; 0A /r                [8086]
# OR reg16,r/m16                ; o16 0B /r            [8086]
# OR reg32,r/m32                ; o32 0B /r            [386]

# OR r/m8,imm8                  ; 80 /1 ib             [8086]
# OR r/m16,imm16                ; o16 81 /1 iw         [8086]
# OR r/m32,imm32                ; o32 81 /1 id         [386]

# OR r/m16,imm8                 ; o16 83 /1 ib         [8086]
# OR r/m32,imm8                 ; o32 83 /1 ib         [386]

# OR AL,imm8                    ; 0C ib                [8086]
# OR AX,imm16                   ; o16 0D iw            [8086]
# OR EAX,imm32                  ; o32 0D id            [386]

# |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
# |BYTE| qualifier is necessary to force NASM to generate this form of the
# instruction.

# The MMX instruction |POR| (see section A.129 <#section-A.129>) performs
# the same operation on the 64-bit MMX registers.


#       A.111 |OUT|: Output Data to I/O Port

# OUT imm8,AL                   ; E6 ib                [8086]
# OUT imm8,AX                   ; o16 E7 ib            [8086]
# OUT imm8,EAX                  ; o32 E7 ib            [386]
# OUT DX,AL                     ; EE                   [8086]
# OUT DX,AX                     ; o16 EF               [8086]
# OUT DX,EAX                    ; o32 EF               [386]

# |IN| 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 |DX|. See also
# |IN| (section A.78 <#section-A.78>).


#       A.112 |OUTSB|, |OUTSW|, |OUTSD|: Output String to I/O Port

# OUTSB                         ; 6E                   [186]

# OUTSW                         ; o16 6F               [186]

# OUTSD                         ; o32 6F               [386]

# |OUTSB| loads a byte from |[DS:SI]| or |[DS:ESI]| and writes it to the
# I/O port specified in |DX|. It then increments or decrements (depending
# on the direction flag: increments if the flag is clear, decrements if it
# is set) |SI| or |ESI|.

# The register used is |SI| if the address size is 16 bits, and |ESI| if
# it is 32 bits. If you need to use an address size not equal to the
# current |BITS| setting, you can use an explicit |a16| or |a32| prefix.

# The segment register used to load from |[SI]| or |[ESI]| can be
# overridden by using a segment register name as a prefix (for example,
# |es outsb|).

# |OUTSW| and |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 |REP| prefix may be used to repeat the instruction |CX| (or |ECX| -
# again, the address size chooses which) times.


#       A.113 |PACKSSDW|, |PACKSSWB|, |PACKUSWB|: Pack Data

# PACKSSDW mmxreg,r/m64         ; 0F 6B /r             [PENT,MMX]
# PACKSSWB mmxreg,r/m64         ; 0F 63 /r             [PENT,MMX]
# PACKUSWB mmxreg,r/m64         ; 0F 67 /r             [PENT,MMX]

# All these instructions start by forming a notional 128-bit word by
# placing the source (second) operand on the left of the destination
# (first) operand. |PACKSSDW| then splits this 128-bit word into four
# doublewords, converts each to a word, and loads them side by side into
# the destination register; |PACKSSWB| and |PACKUSWB| both split the
# 128-bit word into eight words, converts each to a byte, and loads
# /those/ side by side into the destination register.

# |PACKSSDW| and |PACKSSWB| perform signed saturation when reducing the
# length of numbers: if the number is too large to fit into the reduced
# space, they replace it by the largest signed number (|7FFFh| or |7Fh|)
# that /will/ fit, and if it is too small then they replace it by the
# smallest signed number (|8000h| or |80h|) that will fit. |PACKUSWB|
# performs unsigned saturation: it treats its input as unsigned, and
# replaces it by the largest unsigned number that will fit.


#       A.114 |PADDxx|: MMX Packed Addition

# PADDB mmxreg,r/m64            ; 0F FC /r             [PENT,MMX]
# PADDW mmxreg,r/m64            ; 0F FD /r             [PENT,MMX]
# PADDD mmxreg,r/m64            ; 0F FE /r             [PENT,MMX]

# PADDSB mmxreg,r/m64           ; 0F EC /r             [PENT,MMX]
# PADDSW mmxreg,r/m64           ; 0F ED /r             [PENT,MMX]

# PADDUSB mmxreg,r/m64          ; 0F DC /r             [PENT,MMX]
# PADDUSW mmxreg,r/m64          ; 0F DD /r             [PENT,MMX]

# |PADDxx| all perform packed addition between their two 64-bit operands,
# storing the result in the destination (first) operand. The |PADDxB|
# forms treat the 64-bit operands as vectors of eight bytes, and add each
# byte individually; |PADDxW| treat the operands as vectors of four words;
# and |PADDD| treats its operands as vectors of two doublewords.

# |PADDSB| and |PADDSW| perform signed saturation on the sum of each pair
# of bytes or words: if the result of an addition is too large or too
# small to fit into a signed byte or word result, it is clipped
# (saturated) to the largest or smallest value which /will/ fit. |PADDUSB|
# and |PADDUSW| similarly perform unsigned saturation, clipping to |0FFh|
# or |0FFFFh| if the result is larger than that.


#       A.115 |PADDSIW|: MMX Packed Addition to Implicit Destination

# PADDSIW mmxreg,r/m64          ; 0F 51 /r             [CYRIX,MMX]

# |PADDSIW|, specific to the Cyrix extensions to the MMX instruction set,
# performs the same function as |PADDSW|, except that the result is not
# placed in the register specified by the first operand, but instead in
# the register whose number differs from the first operand only in the
# last bit. So |PADDSIW MM0,MM2| would put the result in |MM1|, but
# |PADDSIW MM1,MM2| would put the result in |MM0|.


#       A.116 |PAND|, |PANDN|: MMX Bitwise AND and AND-NOT

# PAND mmxreg,r/m64             ; 0F DB /r             [PENT,MMX]
# PANDN mmxreg,r/m64            ; 0F DF /r             [PENT,MMX]

# |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.

# |PANDN| performs the same operation, but performs a one's complement
# operation on the destination (first) operand first.


#       A.117 |PAVEB|: MMX Packed Average

# PAVEB mmxreg,r/m64            ; 0F 50 /r             [CYRIX,MMX]

# |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.


#       A.118 |PCMPxx|: MMX Packed Comparison

# PCMPEQB mmxreg,r/m64          ; 0F 74 /r             [PENT,MMX]
# PCMPEQW mmxreg,r/m64          ; 0F 75 /r             [PENT,MMX]
# PCMPEQD mmxreg,r/m64          ; 0F 76 /r             [PENT,MMX]

# PCMPGTB mmxreg,r/m64          ; 0F 64 /r             [PENT,MMX]
# PCMPGTW mmxreg,r/m64          ; 0F 65 /r             [PENT,MMX]
# PCMPGTD mmxreg,r/m64          ; 0F 66 /r             [PENT,MMX]

# The |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.

# |PCMPxxB| treats the operands as vectors of eight bytes, |PCMPxxW|
# treats them as vectors of four words, and |PCMPxxD| as two doublewords.

# |PCMPEQx| sets the corresponding element of the destination operand to
# all ones if the two elements compared are equal; |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.


#       A.119 |PDISTIB|: MMX Packed Distance and Accumulate with Implied
#       Register

# PDISTIB mmxreg,mem64          ; 0F 54 /r             [CYRIX,MMX]

# |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 |PADDUSB|.

# The implied output register is found in the same way as |PADDSIW|
# (section A.115 <#section-A.115>).

# Note that |PDISTIB| cannot take a register as its second source operand.


#       A.120 |PMACHRIW|: MMX Packed Multiply and Accumulate with Rounding

# PMACHRIW mmxreg,mem64         ; 0F 5E /r             [CYRIX,MMX]

# |PMACHRIW| acts almost identically to |PMULHRIW| (section A.123
# <#section-A.123>), but instead of /storing/ its result in the implied
# destination register, it /adds/ its result, as four packed words, to the
# implied destination register. No saturation is done: the addition can
# wrap around.

# Note that |PMACHRIW| cannot take a register as its second source operand.


#       A.121 |PMADDWD|: MMX Packed Multiply and Add

# PMADDWD mmxreg,r/m64          ; 0F F5 /r             [PENT,MMX]

# |PMADDWD| treats its two inputs as vectors of four signed words. It
# multiplies corresponding elements of the two operands, giving four
# signed doubleword results. The top two of these are added and placed in
# the top 32 bits of the destination (first) operand; the bottom two are
# added and placed in the bottom 32 bits.


#       A.122 |PMAGW|: MMX Packed Magnitude

# PMAGW mmxreg,r/m64            ; 0F 52 /r             [CYRIX,MMX]

# |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.


#       A.123 |PMULHRW|, |PMULHRIW|: MMX Packed Multiply High with Rounding

# PMULHRW mmxreg,r/m64          ; 0F 59 /r             [CYRIX,MMX]
# PMULHRIW mmxreg,r/m64         ; 0F 5D /r             [CYRIX,MMX]

# These instructions, specific to the Cyrix MMX extensions, treat their
# operands as vectors of four signed words. Words in corresponding
# positions are multiplied, to give a 32-bit value in which bits 30 and 31
# are guaranteed equal. Bits 30 to 15 of this value (bit mask
# |0x7FFF8000|) are taken and stored in the corresponding position of the
# destination operand, after first rounding the low bit (equivalent to
# adding |0x4000| before extracting bits 30 to 15).

# For |PMULHRW|, the destination operand is the first operand; for
# |PMULHRIW| the destination operand is implied by the first operand in
# the manner of |PADDSIW| (section A.115 <#section-A.115>).


#       A.124 |PMULHW|, |PMULLW|: MMX Packed Multiply

# PMULHW mmxreg,r/m64           ; 0F E5 /r             [PENT,MMX]
# PMULLW mmxreg,r/m64           ; 0F D5 /r             [PENT,MMX]

# |PMULxW| treats its two inputs as vectors of four signed words. It
# multiplies corresponding elements of the two operands, giving four
# signed doubleword results.

# |PMULHW| then stores the top 16 bits of each doubleword in the
# destination (first) operand; |PMULLW| stores the bottom 16 bits of each
# doubleword in the destination operand.


#       A.125 |PMVccZB|: MMX Packed Conditional Move

# PMVZB mmxreg,mem64            ; 0F 58 /r             [CYRIX,MMX]
# PMVNZB mmxreg,mem64           ; 0F 5A /r             [CYRIX,MMX]
# PMVLZB mmxreg,mem64           ; 0F 5B /r             [CYRIX,MMX]
# 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
# /implied/ operand (specified in the same way as |PADDSIW|, in section
# A.115 <#section-A.115>).

# |PMVZB| performs each move if the corresponding byte in the implied
# operand is zero. |PMVNZB| moves if the byte is non-zero. |PMVLZB| moves
# if the byte is less than zero, and |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.


#       A.126 |POP|: Pop Data from Stack

# POP reg16                     ; o16 58+r             [8086]
# POP reg32                     ; o32 58+r             [386]

# POP r/m16                     ; o16 8F /0            [8086]
# POP r/m32                     ; o32 8F /0            [386]

# POP CS                        ; 0F                   [8086,UNDOC]
# POP DS                        ; 1F                   [8086]
# POP ES                        ; 07                   [8086]
# POP SS                        ; 17                   [8086]
# POP FS                        ; 0F A1                [386]
# POP GS                        ; 0F A9                [386]

# |POP| loads a value from the stack (from |[SS:SP]| or |[SS:ESP]|) and
# then increments the stack pointer.

# The address-size attribute of the instruction determines whether |SP| or
# |ESP| is used as the stack pointer: to deliberately override the default
# given by the |BITS| setting, you can use an |a16| or |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 |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 |o16| or
# |o32| prefix.

# The above opcode listings give two forms for general-purpose register
# pop instructions: for example, |POP BX| has the two forms |5B| and |8F
# C3|. NASM will always generate the shorter form when given |POP BX|.
# NDISASM will disassemble both.

# |POP CS| is not a documented instruction, and is not supported on any
# processor above the 8086 (since they use |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.


#       A.127 |POPAx|: Pop All General-Purpose Registers

# POPA                          ; 61                   [186]
# POPAW                         ; o16 61               [186]
# POPAD                         ; o32 61               [386]

# |POPAW| pops a word from the stack into each of, successively, |DI|,
# |SI|, |BP|, nothing (it discards a word from the stack which was a
# placeholder for |SP|), |BX|, |DX|, |CX| and |AX|. It is intended to
# reverse the operation of |PUSHAW| (see section A.135 <#section-A.135>),
# but it ignores the value for |SP| that was pushed on the stack by |PUSHAW|.

# |POPAD| pops twice as much data, and places the results in |EDI|, |ESI|,
# |EBP|, nothing (placeholder for |ESP|), |EBX|, |EDX|, |ECX| and |EAX|.
# It reverses the operation of |PUSHAD|.

# |POPA| is an alias mnemonic for either |POPAW| or |POPAD|, depending on
# the current |BITS| setting.

# Note that the registers are popped in reverse order of their numeric
# values in opcodes (see section A.2.1 <#section-A.2.1>).


#       A.128 |POPFx|: Pop Flags Register

# POPF                          ; 9D                   [186]
# POPFW                         ; o16 9D               [186]
# POPFD                         ; o32 9D               [386]

# |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). |POPFD| pops a doubleword and stores it in the entire flags
# register.

# |POPF| is an alias mnemonic for either |POPFW| or |POPFD|, depending on
# the current |BITS| setting.

# See also |PUSHF| (section A.136 <#section-A.136>).


#       A.129 |POR|: MMX Bitwise OR

# POR mmxreg,r/m64              ; 0F EB /r             [PENT,MMX]

# |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.


#       A.130 |PSLLx|, |PSRLx|, |PSRAx|: MMX Bit Shifts

# PSLLW mmxreg,r/m64            ; 0F F1 /r             [PENT,MMX]
# PSLLW mmxreg,imm8             ; 0F 71 /6 ib          [PENT,MMX]

# PSLLD mmxreg,r/m64            ; 0F F2 /r             [PENT,MMX]
# PSLLD mmxreg,imm8             ; 0F 72 /6 ib          [PENT,MMX]

# PSLLQ mmxreg,r/m64            ; 0F F3 /r             [PENT,MMX]
# PSLLQ mmxreg,imm8             ; 0F 73 /6 ib          [PENT,MMX]

# PSRAW mmxreg,r/m64            ; 0F E1 /r             [PENT,MMX]
# PSRAW mmxreg,imm8             ; 0F 71 /4 ib          [PENT,MMX]

# PSRAD mmxreg,r/m64            ; 0F E2 /r             [PENT,MMX]
# PSRAD mmxreg,imm8             ; 0F 72 /4 ib          [PENT,MMX]

# PSRLW mmxreg,r/m64            ; 0F D1 /r             [PENT,MMX]
# PSRLW mmxreg,imm8             ; 0F 71 /2 ib          [PENT,MMX]

# PSRLD mmxreg,r/m64            ; 0F D2 /r             [PENT,MMX]
# PSRLD mmxreg,imm8             ; 0F 72 /2 ib          [PENT,MMX]

# PSRLQ mmxreg,r/m64            ; 0F D3 /r             [PENT,MMX]
# PSRLQ mmxreg,imm8             ; 0F 73 /2 ib          [PENT,MMX]

# |PSxxQ| perform simple bit shifts on the 64-bit MMX registers: the
# destination (first) operand is shifted left or right by the number of
# bits given in the source (second) operand, and the vacated bits are
# filled in with zeros (for a logical shift) or copies of the original
# sign bit (for an arithmetic right shift).

# |PSxxW| and |PSxxD| perform packed bit shifts: the destination operand
# is treated as a vector of four words or two doublewords, and each
# element is shifted individually, so bits shifted out of one element do
# not interfere with empty bits coming into the next.

# |PSLLx| and |PSRLx| perform logical shifts: the vacated bits at one end
# of the shifted number are filled with zeros. |PSRAx| performs an
# arithmetic right shift: the vacated bits at the top of the shifted
# number are filled with copies of the original top (sign) bit.


#       A.131 |PSUBxx|: MMX Packed Subtraction

# PSUBB mmxreg,r/m64            ; 0F F8 /r             [PENT,MMX]
# PSUBW mmxreg,r/m64            ; 0F F9 /r             [PENT,MMX]
# PSUBD mmxreg,r/m64            ; 0F FA /r             [PENT,MMX]

# PSUBSB mmxreg,r/m64           ; 0F E8 /r             [PENT,MMX]
# PSUBSW mmxreg,r/m64           ; 0F E9 /r             [PENT,MMX]

# PSUBUSB mmxreg,r/m64          ; 0F D8 /r             [PENT,MMX]
# PSUBUSW mmxreg,r/m64          ; 0F D9 /r             [PENT,MMX]

# |PSUBxx| all perform packed subtraction between their two 64-bit
# operands, storing the result in the destination (first) operand. The
# |PSUBxB| forms treat the 64-bit operands as vectors of eight bytes, and
# subtract each byte individually; |PSUBxW| treat the operands as vectors
# of four words; and |PSUBD| treats its operands as vectors of two
# doublewords.

# In all cases, the elements of the operand on the right are subtracted
# from the corresponding elements of the operand on the left, not the
# other way round.

# |PSUBSB| and |PSUBSW| perform signed saturation on the sum of each pair
# of bytes or words: if the result of a subtraction is too large or too
# small to fit into a signed byte or word result, it is clipped
# (saturated) to the largest or smallest value which /will/ fit. |PSUBUSB|
# and |PSUBUSW| similarly perform unsigned saturation, clipping to |0FFh|
# or |0FFFFh| if the result is larger than that.


#       A.132 |PSUBSIW|: MMX Packed Subtract with Saturation to Implied
#       Destination

# PSUBSIW mmxreg,r/m64          ; 0F 55 /r             [CYRIX,MMX]

# |PSUBSIW|, specific to the Cyrix extensions to the MMX instruction set,
# performs the same function as |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 |PADDSIW| (section
# A.115 <#section-A.115>).


#       A.133 |PUNPCKxxx|: Unpack Data

# PUNPCKHBW mmxreg,r/m64        ; 0F 68 /r             [PENT,MMX]
# PUNPCKHWD mmxreg,r/m64        ; 0F 69 /r             [PENT,MMX]
# PUNPCKHDQ mmxreg,r/m64        ; 0F 6A /r             [PENT,MMX]

# PUNPCKLBW mmxreg,r/m64        ; 0F 60 /r             [PENT,MMX]
# PUNPCKLWD mmxreg,r/m64        ; 0F 61 /r             [PENT,MMX]
# PUNPCKLDQ mmxreg,r/m64        ; 0F 62 /r             [PENT,MMX]

# |PUNPCKxx| all treat their operands as vectors, and produce a new vector
# generated by interleaving elements from the two inputs. The |PUNPCKHxx|
# instructions start by throwing away the bottom half of each input
# operand, and the |PUNPCKLxx| instructions throw away the top half.

# The remaining elements, totalling 64 bits, are then interleaved into the
# destination, alternating elements from the second (source) operand and
# the first (destination) operand: so the leftmost element in the result
# always comes from the second operand, and the rightmost from the
# destination.

# |PUNPCKxBW| works a byte at a time, |PUNPCKxWD| a word at a time, and
# |PUNPCKxDQ| a doubleword at a time.

# So, for example, if the first operand held |0x7A6A5A4A3A2A1A0A| and the
# second held |0x7B6B5B4B3B2B1B0B|, then:

#     * |PUNPCKHBW| would return |0x7B7A6B6A5B5A4B4A|.
#     * |PUNPCKHWD| would return |0x7B6B7A6A5B4B5A4A|.
#     * |PUNPCKHDQ| would return |0x7B6B5B4B7A6A5A4A|.
#     * |PUNPCKLBW| would return |0x3B3A2B2A1B1A0B0A|.
#     * |PUNPCKLWD| would return |0x3B2B3A2A1B0B1A0A|.
#     * |PUNPCKLDQ| would return |0x3B2B1B0B3A2A1A0A|.


#       A.134 |PUSH|: Push Data on Stack

# PUSH reg16                    ; o16 50+r             [8086]
# PUSH reg32                    ; o32 50+r             [386]

# PUSH r/m16                    ; o16 FF /6            [8086]
# PUSH r/m32                    ; o32 FF /6            [386]

# PUSH CS                       ; 0E                   [8086]
# PUSH DS                       ; 1E                   [8086]
# PUSH ES                       ; 06                   [8086]
# PUSH SS                       ; 16                   [8086]
# PUSH FS                       ; 0F A0                [386]
# PUSH GS                       ; 0F A8                [386]

# PUSH imm8                     ; 6A ib                [286]
# PUSH imm16                    ; o16 68 iw            [286]
# PUSH imm32                    ; o32 68 id            [386]

# |PUSH| decrements the stack pointer (|SP| or |ESP|) by 2 or 4, and then
# stores the given value at |[SS:SP]| or |[SS:ESP]|.

# The address-size attribute of the instruction determines whether |SP| or
# |ESP| is used as the stack pointer: to deliberately override the default
# given by the |BITS| setting, you can use an |a16| or |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 |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
# |o16| or |o32| prefix.

# The above opcode listings give two forms for general-purpose register
# push instructions: for example, |PUSH BX| has the two forms |53| and |FF
# F3|. NASM will always generate the shorter form when given |PUSH BX|.
# NDISASM will disassemble both.

# Unlike the undocumented and barely supported |POP CS|, |PUSH CS| is a
# perfectly valid and sensible instruction, supported on all processors.

# The instruction |PUSH SP| may be used to distinguish an 8086 from later
# processors: on an 8086, the value of |SP| stored is the value it has
# /after/ the push instruction, whereas on later processors it is the
# value /before/ the push instruction.


#       A.135 |PUSHAx|: Push All General-Purpose Registers

# PUSHA                         ; 60                   [186]
# PUSHAD                        ; o32 60               [386]
# PUSHAW                        ; o16 60               [186]

# |PUSHAW| pushes, in succession, |AX|, |CX|, |DX|, |BX|, |SP|, |BP|, |SI|
# and |DI| on the stack, decrementing the stack pointer by a total of 16.

# |PUSHAD| pushes, in succession, |EAX|, |ECX|, |EDX|, |EBX|, |ESP|,
# |EBP|, |ESI| and |EDI| on the stack, decrementing the stack pointer by a
# total of 32.

# In both cases, the value of |SP| or |ESP| pushed is its /original/
# value, as it had before the instruction was executed.

# |PUSHA| is an alias mnemonic for either |PUSHAW| or |PUSHAD|, depending
# on the current |BITS| setting.

# Note that the registers are pushed in order of their numeric values in
# opcodes (see section A.2.1 <#section-A.2.1>).

# See also |POPA| (section A.127 <#section-A.127>).


#       A.136 |PUSHFx|: Push Flags Register

# PUSHF                         ; 9C                   [186]
# PUSHFD                        ; o32 9C               [386]
# PUSHFW                        ; o16 9C               [186]

# |PUSHFW| 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). |PUSHFD| pops a doubleword and stores it in the entire flags
# register.

# |PUSHF| is an alias mnemonic for either |PUSHFW| or |PUSHFD|, depending
# on the current |BITS| setting.

# See also |POPF| (section A.128 <#section-A.128>).


#       A.137 |PXOR|: MMX Bitwise XOR

# PXOR mmxreg,r/m64             ; 0F EF /r             [PENT,MMX]

# |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.


#       A.138 |RCL|, |RCR|: Bitwise Rotate through Carry Bit

# RCL r/m8,1                    ; D0 /2                [8086]
# RCL r/m8,CL                   ; D2 /2                [8086]
# RCL r/m8,imm8                 ; C0 /2 ib             [286]
# RCL r/m16,1                   ; o16 D1 /2            [8086]
# RCL r/m16,CL                  ; o16 D3 /2            [8086]
# RCL r/m16,imm8                ; o16 C1 /2 ib         [286]
# RCL r/m32,1                   ; o32 D1 /2            [386]
# RCL r/m32,CL                  ; o32 D3 /2            [386]
# RCL r/m32,imm8                ; o32 C1 /2 ib         [386]

# RCR r/m8,1                    ; D0 /3                [8086]
# RCR r/m8,CL                   ; D2 /3                [8086]
# RCR r/m8,imm8                 ; C0 /3 ib             [286]
# RCR r/m16,1                   ; o16 D1 /3            [8086]
# RCR r/m16,CL                  ; o16 D3 /3            [8086]
# RCR r/m16,imm8                ; o16 C1 /3 ib         [286]
# RCR r/m32,1                   ; o32 D1 /3            [386]
# RCR r/m32,CL                  ; o32 D3 /3            [386]
# RCR r/m32,imm8                ; o32 C1 /3 ib         [386]

# |RCL| and |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 |RCR AL,1|, a 9-bit
# rotation is performed in which |AL| is shifted left by 1, the top bit of
# |AL| moves into the carry flag, and the original value of the carry flag
# is placed in the low bit of |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 |C1| byte)
# form of |RCL foo,1| by using a |BYTE| prefix: |RCL foo,BYTE 1|.
# Similarly with |RCR|.


#       A.139 |RDMSR|: Read Model-Specific Registers

# RDMSR                         ; 0F 32                [PENT]

# |RDMSR| reads the processor Model-Specific Register (MSR) whose index is
# stored in |ECX|, and stores the result in |EDX:EAX|. See also |WRMSR|
# (section A.165 <#section-A.165>).


#       A.140 |RDPMC|: Read Performance-Monitoring Counters

# RDPMC                         ; 0F 33                [P6]

# |RDPMC| reads the processor performance-monitoring counter whose index
# is stored in |ECX|, and stores the result in |EDX:EAX|.


#       A.141 |RDTSC|: Read Time-Stamp Counter

# RDTSC                         ; 0F 31                [PENT]

# |RDTSC| reads the processor's time-stamp counter into |EDX:EAX|.


#       A.142 |RET|, |RETF|, |RETN|: Return from Procedure Call

# RET                           ; C3                   [8086]
# RET imm16                     ; C2 iw                [8086]

# RETF                          ; CB                   [8086]
# RETF imm16                    ; CA iw                [8086]

# RETN                          ; C3                   [8086]
# RETN imm16                    ; C2 iw                [8086]

# |RET|, and its exact synonym |RETN|, pop |IP| or |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
# |imm16| bytes after popping the return address.

# |RETF| executes a far return: after popping |IP|/|EIP|, it then pops
# |CS|, and /then/ increments the stack pointer by the optional argument
# if present.


#       A.143 |ROL|, |ROR|: Bitwise Rotate

# ROL r/m8,1                    ; D0 /0                [8086]
# ROL r/m8,CL                   ; D2 /0                [8086]
# ROL r/m8,imm8                 ; C0 /0 ib             [286]
# ROL r/m16,1                   ; o16 D1 /0            [8086]
# ROL r/m16,CL                  ; o16 D3 /0            [8086]
# ROL r/m16,imm8                ; o16 C1 /0 ib         [286]
# ROL r/m32,1                   ; o32 D1 /0            [386]
# ROL r/m32,CL                  ; o32 D3 /0            [386]
# ROL r/m32,imm8                ; o32 C1 /0 ib         [386]

# ROR r/m8,1                    ; D0 /1                [8086]
# ROR r/m8,CL                   ; D2 /1                [8086]
# ROR r/m8,imm8                 ; C0 /1 ib             [286]
# ROR r/m16,1                   ; o16 D1 /1            [8086]
# ROR r/m16,CL                  ; o16 D3 /1            [8086]
# ROR r/m16,imm8                ; o16 C1 /1 ib         [286]
# ROR r/m32,1                   ; o32 D1 /1            [386]
# ROR r/m32,CL                  ; o32 D3 /1            [386]
# ROR r/m32,imm8                ; o32 C1 /1 ib         [386]

# |ROL| and |ROR| perform a bitwise rotation operation on the given
# source/destination (first) operand. Thus, for example, in the operation
# |ROR AL,1|, an 8-bit rotation is performed in which |AL| is shifted left
# by 1 and the original top bit of |AL| moves round into the low bit.

# The number of bits to rotate by is given by the second operand. Only the
# bottom 3, 4 or 5 bits (depending on the source operand size) of the
# rotation count are considered by processors above the 8086.

# You can force the longer (286 and upwards, beginning with a |C1| byte)
# form of |ROL foo,1| by using a |BYTE| prefix: |ROL foo,BYTE 1|.
# Similarly with |ROR|.


#       A.144 |RSM|: Resume from System-Management Mode

# RSM                           ; 0F AA                [PENT]

# |RSM| returns the processor to its normal operating mode when it was in
# System-Management Mode.


#       A.145 |SAHF|: Store AH to Flags

# SAHF                          ; 9E                   [8086]

# |SAHF| sets the low byte of the flags word according to the contents of
# the |AH| register. See also |LAHF| (section A.90 <#section-A.90>).


#       A.146 |SAL|, |SAR|: Bitwise Arithmetic Shifts

# SAL r/m8,1                    ; D0 /4                [8086]
# SAL r/m8,CL                   ; D2 /4                [8086]
# SAL r/m8,imm8                 ; C0 /4 ib             [286]
# SAL r/m16,1                   ; o16 D1 /4            [8086]
# SAL r/m16,CL                  ; o16 D3 /4            [8086]
# SAL r/m16,imm8                ; o16 C1 /4 ib         [286]
# SAL r/m32,1                   ; o32 D1 /4            [386]
# SAL r/m32,CL                  ; o32 D3 /4            [386]
# SAL r/m32,imm8                ; o32 C1 /4 ib         [386]

# SAR r/m8,1                    ; D0 /0                [8086]
# SAR r/m8,CL                   ; D2 /0                [8086]
# SAR r/m8,imm8                 ; C0 /0 ib             [286]
# xxSAR r/m16,1                   ; o16 D1 /0            [8086]
# SAR r/m16,CL                  ; o16 D3 /0            [8086]
# SAR r/m16,imm8                ; o16 C1 /0 ib         [286]
# xxSAR r/m32,1                   ; o32 D1 /0            [386]
# SAR r/m32,CL                  ; o32 D3 /0            [386]
# SAR r/m32,imm8                ; o32 C1 /0 ib         [386]

# |SAL| and |SAR| perform an arithmetic shift operation on the given
# source/destination (first) operand. The vacated bits are filled with
# zero for |SAL|, and with copies of the original high bit of the source
# operand for |SAR|.

# |SAL| is a synonym for |SHL| (see section A.152 <#section-A.152>). NASM
# will assemble either one to the same code, but NDISASM will always
# disassemble that code as |SHL|.

# The number of bits to shift by is given by the second operand. Only the
# bottom 3, 4 or 5 bits (depending on the source operand size) of the
# shift count are considered by processors above the 8086.

# You can force the longer (286 and upwards, beginning with a |C1| byte)
# form of |SAL foo,1| by using a |BYTE| prefix: |SAL foo,BYTE 1|.
# Similarly with |SAR|.


#       A.147 |SALC|: Set AL from Carry Flag

# SALC                          ; D6                   [8086,UNDOC]

# |SALC| is an early undocumented instruction similar in concept to
# |SETcc| (section A.150 <#section-A.150>). Its function is to set |AL| to
# zero if the carry flag is clear, or to |0xFF| if it is set.


#       A.148 |SBB|: Subtract with Borrow

# SBB r/m8,reg8                 ; 18 /r                [8086]
# SBB r/m16,reg16               ; o16 19 /r            [8086]
# SBB r/m32,reg32               ; o32 19 /r            [386]

# SBB reg8,r/m8                 ; 1A /r                [8086]
# SBB reg16,r/m16               ; o16 1B /r            [8086]
# SBB reg32,r/m32               ; o32 1B /r            [386]

# SBB r/m8,imm8                 ; 80 /3 ib             [8086]
# SBB r/m16,imm16               ; o16 81 /3 iw         [8086]
# SBB r/m32,imm32               ; o32 81 /3 id         [386]

# SBB r/m16,imm8                ; o16 83 /3 ib         [8086]
# SBB r/m32,imm8                ; o32 83 /3 ib         [8086]

# SBB AL,imm8                   ; 1C ib                [8086]
# SBB AX,imm16                  ; o16 1D iw            [8086]
# SBB EAX,imm32                 ; o32 1D id            [386]

# |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 |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
# |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 |SUB| (section A.159 <#section-A.159>).


#       A.149 |SCASB|, |SCASW|, |SCASD|: Scan String

# SCASB                         ; AE                   [8086]
# SCASW                         ; o16 AF               [8086]
# SCASD                         ; o32 AF               [386]

# |SCASB| compares the byte in |AL| with the byte at |[ES:DI]| or
# |[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) |DI| (or |EDI|).

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

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

# |SCASW| and |SCASD| work in the same way, but they compare a word to
# |AX| or a doubleword to |EAX| instead of a byte to |AL|, and increment
# or decrement the addressing registers by 2 or 4 instead of 1.

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


#       A.150 |SETcc|: Set Register from Condition

# SETcc r/m8                    ; 0F 90+cc /2          [386]

# |SETcc| sets the given 8-bit operand to zero if its condition is not
# satisfied, and to 1 if it is.


#       A.151 |SGDT|, |SIDT|, |SLDT|: Store Descriptor Table Pointers

# SGDT mem                      ; 0F 01 /0             [286,PRIV]
# SIDT mem                      ; 0F 01 /1             [286,PRIV]
# SLDT r/m16                    ; 0F 00 /0             [286,PRIV]

# |SGDT| and |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 /linear/ addresses,
# rather than segment/offset pairs.

# |SLDT| stores the segment selector corresponding to the LDT (local
# descriptor table) into the given operand.

# See also |LGDT|, |LIDT| and |LLDT| (section A.95 <#section-A.95>).


#       A.152 |SHL|, |SHR|: Bitwise Logical Shifts

# SHL r/m8,1                    ; D0 /4                [8086]
# SHL r/m8,CL                   ; D2 /4                [8086]
# SHL r/m8,imm8                 ; C0 /4 ib             [286]
# SHL r/m16,1                   ; o16 D1 /4            [8086]
# SHL r/m16,CL                  ; o16 D3 /4            [8086]
# SHL r/m16,imm8                ; o16 C1 /4 ib         [286]
# SHL r/m32,1                   ; o32 D1 /4            [386]
# SHL r/m32,CL                  ; o32 D3 /4            [386]
# SHL r/m32,imm8                ; o32 C1 /4 ib         [386]

# SHR r/m8,1                    ; D0 /5                [8086]
# SHR r/m8,CL                   ; D2 /5                [8086]
# SHR r/m8,imm8                 ; C0 /5 ib             [286]
# SHR r/m16,1                   ; o16 D1 /5            [8086]
# SHR r/m16,CL                  ; o16 D3 /5            [8086]
# SHR r/m16,imm8                ; o16 C1 /5 ib         [286]
# SHR r/m32,1                   ; o32 D1 /5            [386]
# SHR r/m32,CL                  ; o32 D3 /5            [386]
# SHR r/m32,imm8                ; o32 C1 /5 ib         [386]

# |SHL| and |SHR| perform a logical shift operation on the given
# source/destination (first) operand. The vacated bits are filled with zero.

# A synonym for |SHL| is |SAL| (see section A.146 <#section-A.146>). NASM
# will assemble either one to the same code, but NDISASM will always
# disassemble that code as |SHL|.

# The number of bits to shift by is given by the second operand. Only the
# bottom 3, 4 or 5 bits (depending on the source operand size) of the
# shift count are considered by processors above the 8086.

# You can force the longer (286 and upwards, beginning with a |C1| byte)
# form of |SHL foo,1| by using a |BYTE| prefix: |SHL foo,BYTE 1|.
# Similarly with |SHR|.


#       A.153 |SHLD|, |SHRD|: Bitwise Double-Precision Shifts

# SHLD r/m16,reg16,imm8         ; o16 0F A4 /r ib      [386]
# SHLD r/m16,reg32,imm8         ; o32 0F A4 /r ib      [386]
# SHLD r/m16,reg16,CL           ; o16 0F A5 /r         [386]
# SHLD r/m16,reg32,CL           ; o32 0F A5 /r         [386]

# SHRD r/m16,reg16,imm8         ; o16 0F AC /r ib      [386]
# SHRD r/m32,reg32,imm8         ; o32 0F AC /r ib      [386]
# SHRD r/m16,reg16,CL           ; o16 0F AD /r         [386]
# SHRD r/m32,reg32,CL           ; o32 0F AD /r         [386]

# |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 /first/ operand according to the
# result of this. The second operand is not modified.

# |SHRD| performs the corresponding right shift: it notionally places the
# second operand to the /left/ of the first, shifts the whole bit string
# right, and updates only the first operand.

# For example, if |EAX| holds |0x01234567| and |EBX| holds |0x89ABCDEF|,
# then the instruction |SHLD EAX,EBX,4| would update |EAX| to hold
# |0x12345678|. Under the same conditions, |SHRD EAX,EBX,4| would update
# |EAX| to hold |0xF0123456|.

# The number of bits to shift by is given by the third operand. Only the
# bottom 5 bits of the shift count are considered.


#       A.154 |SMI|: System Management Interrupt

# SMI                           ; F1                   [386,UNDOC]

# This is an opcode apparently supported by some AMD processors (which is
# why it can generate the same opcode as |INT1|), and places the machine
# into system-management mode, a special debugging mode.


#       A.155 |SMSW|: Store Machine Status Word

# SMSW r/m16                    ; 0F 01 /4             [286,PRIV]

# |SMSW| stores the bottom half of the |CR0| control register (or the
# Machine Status Word, on 286 processors) into the destination operand.
# See also |LMSW| (section A.96 <#section-A.96>).


#       A.156 |STC|, |STD|, |STI|: Set Flags

# STC                           ; F9                   [8086]
# STD                           ; FD                   [8086]
# STI                           ; FB                   [8086]

# These instructions set various flags. |STC| sets the carry flag; |STD|
# sets the direction flag; and |STI| sets the interrupt flag (thus
# enabling interrupts).

# To clear the carry, direction, or interrupt flags, use the |CLC|, |CLD|
# and |CLI| instructions (section A.15 <#section-A.15>). To invert the
# carry flag, use |CMC| (section A.16 <#section-A.16>).


#       A.157 |STOSB|, |STOSW|, |STOSD|: Store Byte to String

# STOSB                         ; AA                   [8086]
# STOSW                         ; o16 AB               [8086]
# STOSD                         ; o32 AB               [386]

# |STOSB| stores the byte in |AL| at |[ES:DI]| or |[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) |DI| (or |EDI|).

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

# Segment override prefixes have no effect for this instruction: the use
# of |ES| for the store to |[DI]| or |[EDI]| cannot be overridden.

# |STOSW| and |STOSD| work in the same way, but they store the word in
# |AX| or the doubleword in |EAX| instead of the byte in |AL|, and
# increment or decrement the addressing registers by 2 or 4 instead of 1.

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


#       A.158 |STR|: Store Task Register

# STR r/m16                     ; 0F 00 /1             [286,PRIV]

# |STR| stores the segment selector corresponding to the contents of the
# Task Register into its operand.


#       A.159 |SUB|: Subtract Integers

# SUB r/m8,reg8                 ; 28 /r                [8086]
# SUB r/m16,reg16               ; o16 29 /r            [8086]
# SUB r/m32,reg32               ; o32 29 /r            [386]

# SUB reg8,r/m8                 ; 2A /r                [8086]
# SUB reg16,r/m16               ; o16 2B /r            [8086]
# SUB reg32,r/m32               ; o32 2B /r            [386]

# SUB r/m8,imm8                 ; 80 /5 ib             [8086]
# SUB r/m16,imm16               ; o16 81 /5 iw         [8086]
# SUB r/m32,imm32               ; o32 81 /5 id         [386]

# SUB r/m16,imm8                ; o16 83 /5 ib         [8086]
# SUB r/m32,imm8                ; o32 83 /5 ib         [386]

# SUB AL,imm8                   ; 2C ib                [8086]
# SUB AX,imm16                  ; o16 2D iw            [8086]
# SUB EAX,imm32                 ; o32 2D id            [386]

# |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 |SBB|
# instruction (section A.148 <#section-A.148>).

# 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
# |BYTE| qualifier is necessary to force NASM to generate this form of the
# instruction.


#       A.160 |TEST|: Test Bits (notional bitwise AND)

# TEST r/m8,reg8                ; 84 /r                [8086]
# TEST r/m16,reg16              ; o16 85 /r            [8086]
# TEST r/m32,reg32              ; o32 85 /r            [386]

# TEST r/m8,imm8                ; F6 /7 ib             [8086]
# TEST r/m16,imm16              ; o16 F7 /7 iw         [8086]
# TEST r/m32,imm32              ; o32 F7 /7 id         [386]

# TEST AL,imm8                  ; A8 ib                [8086]
# TEST AX,imm16                 ; o16 A9 iw            [8086]
# TEST EAX,imm32                ; o32 A9 id            [386]

# |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.


#       A.161 |UMOV|: User Move Data

# UMOV r/m8,reg8                ; 0F 10 /r             [386,UNDOC]
# UMOV r/m16,reg16              ; o16 0F 11 /r         [386,UNDOC]
# UMOV r/m32,reg32              ; o32 0F 11 /r         [386,UNDOC]

# UMOV reg8,r/m8                ; 0F 12 /r             [386,UNDOC]
# UMOV reg16,r/m16              ; o16 0F 13 /r         [386,UNDOC]
# 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 |MOV| instruction, but
# accesses user space.


#       A.162 |VERR|, |VERW|: Verify Segment Readability/Writability

# VERR r/m16                    ; 0F 00 /4             [286,PRIV]

# VERW r/m16                    ; 0F 00 /5             [286,PRIV]

# |VERR| sets the zero flag if the segment specified by the selector in
# its operand can be read from at the current privilege level. |VERW| sets
# the zero flag if the segment can be written.


#       A.163 |WAIT|: Wait for Floating-Point Processor

# WAIT                          ; 9B                   [8086]

# |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, |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.


#       A.164 |WBINVD|: Write Back and Invalidate Cache

# WBINVD                        ; 0F 09                [486]

# |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 |INVD| (section A.84 <#section-A.84>).


#       A.165 |WRMSR|: Write Model-Specific Registers

# WRMSR                         ; 0F 30                [PENT]

# |WRMSR| writes the value in |EDX:EAX| to the processor Model-Specific
# Register (MSR) whose index is stored in |ECX|. See also |RDMSR| (section
# A.139 <#section-A.139>).


#       A.166 |XADD|: Exchange and Add

# XADD r/m8,reg8                ; 0F C0 /r             [486]
# XADD r/m16,reg16              ; o16 0F C1 /r         [486]
# XADD r/m32,reg32              ; o32 0F C1 /r         [486]

# |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 |LOCK| prefix for multi-processor
# synchronisation purposes.


#       A.167 |XBTS|: Extract Bit String

# XBTS reg16,r/m16              ; o16 0F A6 /r         [386,UNDOC]
# XBTS reg32,r/m32              ; o32 0F A6 /r         [386,UNDOC]

# No clear documentation seems to be available for this instruction: the
# best I've been able to find reads `Takes a string of bits from the first
# operand and puts them in the second operand'. It is present only in
# early 386 processors, and conflicts with the opcodes for |CMPXCHG486|.
# NASM supports it only for completeness. Its counterpart is |IBTS| (see
# section A.75 <#section-A.75>).


#       A.168 |XCHG|: Exchange

# XCHG reg8,r/m8                ; 86 /r                [8086]
# XCHG reg16,r/m8               ; o16 87 /r            [8086]
# XCHG reg32,r/m32              ; o32 87 /r            [386]

# XCHG r/m8,reg8                ; 86 /r                [8086]
# XCHG r/m16,reg16              ; o16 87 /r            [8086]
# XCHG r/m32,reg32              ; o32 87 /r            [386]

# XCHG AX,reg16                 ; o16 90+r             [8086]
# XCHG EAX,reg32                ; o32 90+r             [386]
# XCHG reg16,AX                 ; o16 90+r             [8086]
# XCHG reg32,EAX                ; o32 90+r             [386]

# |XCHG| exchanges the values in its two operands. It can be used with a
# |LOCK| prefix for purposes of multi-processor synchronisation.

# |XCHG AX,AX| or |XCHG EAX,EAX| (depending on the |BITS| setting)
# generates the opcode |90h|, and so is a synonym for |NOP| (section A.109
# <#section-A.109>).


#       A.169 |XLATB|: Translate Byte in Lookup Table

# XLATB                         ; D7                   [8086]

# |XLATB| adds the value in |AL|, treated as an unsigned byte, to |BX| or
# |EBX|, and loads the byte from the resulting address (in the segment
# specified by |DS|) back into |AL|.

# The base register used is |BX| if the address size is 16 bits, and |EBX|
# if it is 32 bits. If you need to use an address size not equal to the
# current |BITS| setting, you can use an explicit |a16| or |a32| prefix.

# The segment register used to load from |[BX+AL]| or |[EBX+AL]| can be
# overridden by using a segment register name as a prefix (for example,
# |es xlatb|).


#       A.170 |XOR|: Bitwise Exclusive OR

# XOR r/m8,reg8                 ; 30 /r                [8086]
# XOR r/m16,reg16               ; o16 31 /r            [8086]
# XOR r/m32,reg32               ; o32 31 /r            [386]

# XOR reg8,r/m8                 ; 32 /r                [8086]
# XOR reg16,r/m16               ; o16 33 /r            [8086]
# XOR reg32,r/m32               ; o32 33 /r            [386]

# XOR r/m8,imm8                 ; 80 /6 ib             [8086]
# XOR r/m16,imm16               ; o16 81 /6 iw         [8086]
# XOR r/m32,imm32               ; o32 81 /6 id         [386]

# XOR r/m16,imm8                ; o16 83 /6 ib         [8086]
# XOR r/m32,imm8                ; o32 83 /6 ib         [386]

# XOR AL,imm8                   ; 34 ib                [8086]
# XOR AX,imm16                  ; o16 35 iw            [8086]
# XOR EAX,imm32                 ; o32 35 id            [386]

# |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
# |BYTE| qualifier is necessary to force NASM to generate this form of the
# instruction.

# The MMX instruction |PXOR| (see section A.137 <#section-A.137>) performs
# the same operation on the 64-bit MMX registers.

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