User Guide

x87 Floating-Point Programming 273
24592—Rev. 3.15—November 2009 AMD64 Technology
6.4.7 Stack Management
The stack management instructions move the x87 top-of-stack pointer (TOP) and clear the contents of
stack registers.
Stack Control
• FDECSTP—Floating-Point Decrement Stack-Top Pointer
• FINCSTP—Floating-Point Increment Stack-Top Pointer
The FINCSTP and FDECSTP instructions increment and decrement, respectively, the TOP, modulo-8.
Neither the x87 tag word nor the contents of the floating-point stack itself is updated.
Clear State
• FFREE—Free Floating-Point Register
The FFREE instruction frees a specified stack register by setting the x87 tag-word bits for the register
to all 1s, indicating empty. Neither the stack-register contents nor the stack pointer is modified by this
instruction.
6.4.8 No Operation
This instruction uses processor cycles but generates no result.
• FNOP—Floating-Point No Operation
The FNOP instruction has no operands and writes no result. Its purpose is simply to delay execution of
a sequence of instructions.
6.4.9 Control
The control instructions are used to initialize, save, and restore x87 processor state and to manage x87
exceptions.
Initialize
• FINIT—Floating-Point Initialize
• FNINIT—Floating-Point No-Wait Initialize
1010 +empty
1011 -empty
1100 +denormal
1101 -denormal
Table 6-15. Condition-Code Settings for FXAM (continued)
C3 C2 C0
C1
1
Meaning
Note:
1. C1 is the sign of ST(0).