User Guide

x87 Floating-Point Programming 239
24592—Rev. 3.15—November 2009 AMD64 Technology
Figure 6-1. x87 Registers
These registers include eight 80-bit data registers, three 16-bit registers that hold the x87 control word,
status word, and tag word, two 64-bit registers that hold instruction and data pointers, and an 11-bit
register that holds a permutation of an x87 opcode.
6.2.1 x87 Data Registers
Figure 6-2 on page 240 shows the eight 80-bit data registers in more detail. Typically, x87 instructions
reference these registers as a stack. x87 instructions store operands only in these 80-bit registers or in
memory. They do not (with two exceptions) access the GPR registers, and they do not access the XMM
registers.
Tag Word
Status Word
Control Word
513-321.eps
x87 Data Registers
79 0
fpr0
fpr1
fpr2
fpr3
fpr4
fpr5
fpr6
fpr7
015
63
010
Instruction Pointer (rIP)
Data Pointer (rDP)
Tag Word
Status Word
Control Word
Opcode