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

24594 Rev. 3.10 February 2005 AMD64 Technology• ib, iw, id—Specifies an immediate-operand value. Theopcode determines whether the value is signed or unsigned.The value following the opcode, ModRM, or SIB byte iseither one byte (ib), two bytes (iw), or four bytes (id). Wordand doubleword values start with the low-order byte.• +rb, +rw, +rd, +rq—Specifies a register value that is added tothe hexadecimal byte on the left, forming a one-byte opcode.The result is an instruction that operates on the registerspecified by the register code. Valid register-code values areshown in Table 2-2.• m64—Specifies a quadword (64-bit) operand in memory.• +i—Specifies an x87 floating-point stack operand, ST(i). Thevalue is used only with x87 floating-point instructions. It isadded to the hexadecimal byte on the left, forming a onebyteopcode. Valid values range from 0 to 7.Table 2-2.+rb, +rw, +rd, and +rq Register ValueREX.BBit 1ValueSpecified Register+rb +rw +rd +rq0 AL AX EAX RAX1 CL CX ECX RCX0or no REXPrefix2 DL DX EDX RDX3 BL BX EBX RBX4 AH, SPL 1 SP ESP RSP5 CH, BPL 1 BP EBP RBP1. See “REX Prefixes” on page 14.6 DH, SIL 1 SI ESI RSI7 BH, DIL 1 DI EDI RDIChapter 2: Instruction Overview 47