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Appendix C Instruction Latencies 271
Software Optimization Guide for AMD64 Processors
25112 Rev. 3.06 September 2005
Interpreting Placeholders
The Syntax column for an instruction entry shows the mnemonic for the instruction followed by any
operands. Items in italics are placeholders for operands that you must provide. A placeholder
indicates the size and type of operand that is allowed.
This operand Is a placeholder for
disp8 A byte (8-bit) displacement value
disp16/32 A word (16-bit) or doubleword (32-bit) displacement value
disp32/48 A doubleword (32-bit) or 48-bit displacement value
imm8 A byte (8-bit) immediate value
imm16 A word (16-bit) immediate value
imm32 A doubleword (32-bit) immediate value
mem8 A byte (8-bit) memory location
mem16/32/64 A memory location that contains a word, doubleword, or quadword
mem16/32&mem16/32 A memory location that contains a pair of words or doublewords
mem32/48 A doubleword (32-bit) or 48-bit memory location
mem48 A 48-bit memory location
mem64 A quadword (64-bit) memory location
mem128 A double quadword (128-bit) memory location
mem32real A memory location that contains a single-precision (32-bit) floating-point value
mem64real A memory location that contains a double-precision (64-bit) floating-point value
mem80real A memory location that contains a double-extended-precision (80-bit) floating-point
value
mmreg An MMX™ register
mmreg1 An MMX register defined by bits 5, 4, and 3 of the ModRM byte
mmreg2 An MMX register defined by bits 2, 1, and 0 of the ModRM byte
mreg8 A byte general-purpose register defined by the r/m field (bits 2, 1, and 0) of the
ModRM byte
mreg16/32/64 A word, doubleword, or quadword general-purpose register defined by the r/m field
(bits 2, 1, and 0) of the ModRM byte
reg8 A byte general-purpose register defined by instruction byte(s) or the reg field (bits 5,
4, and 3) of the ModRM byte
reg16/32/64 A word, doubleword, or quadword general-purpose register defined by instruction
byte(s) or the reg field (bits 5, 4, and 3) of the ModRM byte
sreg A segment register (always 16 bits wide)
xmmreg An XMM register
xmmreg1 An XMM register defined by bits 5, 4, and 3 of the ModRM byte
xmmreg2 An XMM register defined by bits 2, 1, and 0 of the ModRM byte