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Volume 4: Base IA-32 Instruction Reference
FRSTOR—Restore FPU State
Description
Loads the FPU state (operating environment and register stack) from the memory area
specified with the source operand. This state data is typically written to the specified
memory location by a previous FSAVE/FNSAVE instruction.
The FPU operating environment consists of the FPU control word, status word, tag
word, instruction pointer, data pointer, and last opcode. See the
Intel
®
64 and IA-32
Architectures Software Developer’s Manual
for the layout in memory of the stored
environment, depending on the operating mode of the processor (protected or real)
and the size of the current address attribute (16-bit or 32-bit). In virtual-8086 mode,
the real mode layouts are used. The contents of the FPU register stack are stored in the
80 bytes immediately follow the operating environment image.
The FRSTOR instruction should be executed in the same operating mode as the
corresponding FSAVE/FNSAVE instruction.
If one or more unmasked exception bits are set in the new FPU status word, a
floating-point exception will be generated. To avoid raising exceptions when loading a
new operating environment, clear all the exception flags in the FPU status word that is
being loaded.
Operation
FPUControlWord
SRC(FPUControlWord);
FPUStatusWord
SRC(FPUStatusWord);
FPUTagWord
SRC(FPUTagWord);
FPUDataPointer
SRC(FPUDataPointer);
FPUInstructionPointer
SRC(FPUInstructionPointer);
FPULastInstructionOpcode
SRC(FPULastInstructionOpcode);
ST(0)
SRC(ST(0));
ST(1)
SRC(ST(1));
ST(2)
SRC(ST(2));
ST(3)
SRC(ST(3));
ST(4)
SRC(ST(4));
ST(5)
SRC(ST(5));
ST(6)
SRC(ST(6));
ST(7)
SRC(ST(7));
FPU Flags Affected
The C0, C1, C2, C3 flags are loaded.
Floating-point Exceptions
None; however, this operation might unmask an existing exception that has been
detected but not generated, because it was masked. Here, the exception is generated
at the completion of the instruction.
Opcode
Instruction
Description
DD /4
FRSTOR
m94/108byte
Load FPU state from
m94byte
or
m108byte
.
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Страница 288: ...Volume 4 Base IA 32 Instruction Reference 4 281 LSS Load Full Pointer See entry for LDS LES LFS LGS LSS ...
Страница 352: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Страница 368: ...Volume 4 Base IA 32 Instruction Reference 4 361 SHL SHR Shift Instructions See entry for SAL SAR SHL SHR ...
Страница 373: ...4 366 Volume 4 Base IA 32 Instruction Reference SIDT Store Interrupt Descriptor Table Register See entry for SGDT SIDT ...
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Страница 590: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Страница 591: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Страница 603: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...
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