AMD amd64 architecture User Manual
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.
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.
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
0
15
63
0
10
Instruction Pointer (rIP)
Data Pointer (rDP)
Tag Word
Status Word
Control Word
Opcode