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

AMD64 Technology 24594 Rev. 3.10 February 20052.3.5 x87 Floating-Point InstructionsRegisters. The x87 floating-point instructions use the x87registers shown in Figure 2-12. There are eight 80-bit dataregisters, three 16-bit registers that hold the x87 control word,status word, and tag word, and three registers (last instructionpointer, last opcode, last data pointer) that hold informationabout the last x87 operation.The physical data registers are named FPR0–FPR7, althoughx87 software references these registers as a stack of registers,named ST(0)–ST(7). The x87 instructions store operands only intheir own 80-bit floating-point registers or in memory. They donot access the GPR or XMM registers.x87 Data Registers79 0fpr0fpr1fpr2fpr3fpr4fpr5fpr6fpr7Instruction Pointer (rIP)Control WordData Pointer (rDP)Status Word63OpcodeTag Word100150513-321.epsFigure 2-12.x87 RegistersData Types. Figure 2-13 on page 41 shows all x87 data types. Theyinclude three floating-point formats (80-bit double-extendedprecision, 64-bit double precision, and 32-bit single precision),three signed-integer formats (quadword, doubleword, and40 Chapter 2: Instruction Overview