Intel 64 and IA-32 Architectures Software Developers Manual Volume 2A, Instruction Set Reference, A-M

Vol. 2 3-5

INSTRUCTION SET REFERENCE, A-M

between +9,223,372,036,854,775,807 and –9,223,372,036,854,775,808

inclusive.

• r/m8 — A byte operand that is either the contents of a byte general-purpose

memory. Byte registers R8L - R15L are available using REX.R in 64-bit mode.

• r/m16 — A word general-purpose register or memory operand used for instruc-

tions whose operand-size attribute is 16 bits. The word general-purpose registers

are: AX, CX, DX, BX, SP, BP, SI, DI. The contents of memory are found at the

address provided by the effective address computation. Word registers R8W -

R15W are available using REX.R in 64-bit mode.

• r/m32 — A doubleword general-purpose register or memory operand used for

instructions whose operand-size attribute is 32 bits. The doubleword general-

purpose registers are: EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI. The contents of

memory are found at the address provided by the effective address computation.

Doubleword registers R8D - R15D are available when using REX.R in 64-bit

mode.

• r/m64 — A quadword general-purpose register or memory operand used for

instructions whose operand-size attribute is 64 bits when using REX.W.

Quadword general-purpose registers are: RAX, RBX, RCX, RDX, RDI, RSI, RBP,

RSP, R8–R15; these are available only in 64-bit mode. The contents of memory

are found at the address provided by the effective address computation.

• m — A 16-, 32- or 64-bit operand in memory.

• m8 — A byte operand in memory, usually expressed as a variable or array name,

but pointed to by the DS:(E)SI or ES:(E)DI registers. In 64-bit mode, it is pointed

to by the RSI or RDI registers.

• m16 — A word operand in memory, usually expressed as a variable or array

name, but pointed to by the DS:(E)SI or ES:(E)DI registers. This nomenclature is

used only with the string instructions.

• m32 — A doubleword operand in memory, usually expressed as a variable or

array name, but pointed to by the DS:(E)SI or ES:(E)DI registers. This nomen-

clature is used only with the string instructions.

• m64 — A memory quadword operand in memory.

• m128 — A memory double quadword operand in memory. This nomenclature is

used only with SSE and SSE2 instructions.

• m16:16, m16:32 & m16:64 — A memory operand containing a far pointer

composed of two numbers. The number to the left of the colon corresponds to the

pointer's segment selector. The number to the right corresponds to its offset.

• m16&32, m16&16, m32&32, m16&64 — A memory operand consisting of

data item pairs whose sizes are indicated on the left and the right side of the

ampersand. All memory addressing modes are allowed. The m16&16 and

m32&32 operands are used by the BOUND instruction to provide an operand

containing an upper and lower bounds for array indices. The m16&32 operand is

used by LIDT and LGDT to provide a word with which to load the limit field, and a