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Volume 3: General-Purpose and System Instructions - Stanford ...

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24594 Rev. 3.10 February 2005 AMD64 TechnologyBits:76543210modreg r/m ModRMREX.R bit of REX prefix canextend this field to 4 bitsREX.B bit of REX prefix canextend this field to 4 bits513-305.epsFigure A-2.ModRM-Byte FormatThe two sections below describe the ModRM oper<strong>and</strong>encodings, first for 32-bit <strong>and</strong> 64-bit references, <strong>and</strong> then for 16-bit references.16-Bit Register <strong>and</strong> Memory References. Table A-12 shows thenotation <strong>and</strong> encoding conventions for register references usingthe ModRM reg field. This table is comparable to Table A-14 onpage 406 but applies only when the address-size is 16-bit.Table A-13 on page 404 shows the notation <strong>and</strong> encodingconventions for 16-bit memory references using the ModRMbyte. This table is comparable to Table A-15 on page 407.Table A-12.ModRM Register References, 16-Bit AddressingMnemonicNotationModRM reg Field/0 /1 /2 /3 /4 /5 /6 /7reg8 AL CL DL BL AH CH DH BHreg16 AX CX DX BX SP BP SI DIreg32 EAX ECX EDX EBX ESP EBP ESI EDImmx MMX0 MMX1 MMX2 MMX3 MMX4 MMX5 MMX6 MMX7xmm XMM0 XMM1 XMM2 XMM3 XMM4 XMM5 XMM6 XMM7sReg ES CS SS DS FS GS iinvalid invalidcReg CR0 CR1 CR2 CR3 CR4 CR5 CR6 CR7dReg DR0 DR1 DR2 DR3 DR4 DR5 DR6 DR7Appendix A: Opcode <strong>and</strong> Oper<strong>and</strong> Encodings 403

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