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Volume 4: IA-32 Intel
®
MMX™ Technology Instruction Reference
EMMS—Empty MMX State
Description
Sets the values of all the tags in the FPU tag word to empty (all ones). This operation
marks the MMX technology registers as available, so they can subsequently be used by
floating-point instructions. (See Figure 7-11 in the
Intel Architecture Software
Developer’s Manual, Volume 1
, for the format of the FPU tag word.) All other MMX
technology instructions (other than the EMMS instruction) set all the tags in FPU tag
word to valid (all zeros).
The EMMS instruction must be used to clear the MMX technology state at the end of all
MMX technology routines and before calling other procedures or subroutines that may
execute floating-point instructions. If a floating-point instruction loads one of the
registers in the FPU register stack before the FPU tag word has been reset by the EMMS
instruction, a floating-point stack overflow can occur that will result in a floating-point
exception or incorrect result.
Operation
FPUTagWord
FFFFH;
Flags Affected
None.
Additional Itanium System Environment Exceptions
Itanium Reg Faults Disabled FP Register Fault if PSR.dfl is 1.
Protected Mode Exceptions
#UD
If EM in CR0 is set.
#NM
If TS in CR0 is set.
#MF
If there is a pending FPU exception.
Real-Address Mode Exceptions
#UD
If EM in CR0 is set.
#NM
If TS in CR0 is set.
#MF
If there is a pending FPU exception.
Virtual-8086 Mode Exceptions
#UD
If EM in CR0 is set.
#NM
If TS in CR0 is set.
#MF
If there is a pending FPU exception.
Opcode
Instruction
Description
0F 77
EMMS
Set the FP tag word to empty.
Summary of Contents for ITANIUM ARCHITECTURE
Page 1: ......
Page 7: ...402 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 199: ...4 192 Volume 4 Base IA 32 Instruction Reference FWAIT Wait See entry for WAIT ...
Page 352: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Page 589: ...4 582 Volume 4 IA 32 SSE Instruction Reference ...
Page 590: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Page 591: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 603: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...
Page 604: ......