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3-4 Vol. 2A
INSTRUCTION SET REFERENCE, A-M
• ptr16:16, ptr16:32 and ptr16:64 — A far pointer, typically to a code segment
different from that of the instruction. The notation 16:16 indicates that the value
of the pointer has two parts. The value to the left of the colon is a 16-bit selector
or value destined for the code segment register. The value to the right
corresponds to the offset within the destination segment. The ptr16:16 symbol is
used when the instruction's operand-size attribute is 16 bits; the ptr16:32
symbol is used when the operand-size attribute is 32 bits; the ptr16:64 symbol is
used when the operand-size attribute is 64 bits.
• r8 — One of the byte general-purpose registers: AL, CL, DL, BL, AH, CH, DH, BH,
BPL, SPL, DIL and SIL; or one of the byte registers (R8L - R15L) available when
using REX.R and 64-bit mode.
• r16 — One of the word general-purpose registers: AX, CX, DX, BX, SP, BP, SI, DI;
or one of the word registers (R8-R15) available when using REX.R and 64-bit
mode.
• r32 — One of the doubleword general-purpose registers: EAX, ECX, EDX, EBX,
ESP, EBP, ESI, EDI; or one of the doubleword registers (R8D - R15D) available
when using REX.R in 64-bit mode.
• r64 — One of the quadword general-purpose registers: RAX, RBX, RCX, RDX,
RDI, RSI, RBP, RSP, R8–R15. These are available when using REX.R and 64-bit
mode.
• imm8 — An immediate byte value. The imm8 symbol is a signed number
between –128 and +127 inclusive. For instructions in which imm8 is combined
with a word or doubleword operand, the immediate value is sign-extended to
form a word or doubleword. The upper byte of the word is filled with the topmost
bit of the immediate value.
• imm16 — An immediate word value used for instructions whose operand-size
attribute is 16 bits. This is a number between –32,768 and +32,767 inclusive.
• imm32 — An immediate doubleword value used for instructions whose
operand-size attribute is 32 bits. It allows the use of a number between
+2,147,483,647 and –2,147,483,648 inclusive.
• imm64 — An immediate quadword value used for instructions whose
operand-size attribute is 64 bits. The value allows the use of a number
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
register (AL, CL, DL, BL, AH, CH, DH, BH, BPL, SPL, DIL and SIL) or a byte from
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.