Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1435

FINIT/FNINIT—Initialize Floating-point Unit
Opcode
9B DB E3
DB E3
Description
Sets the FPU control, status, tag, instruction pointer, and data pointer registers to their
default states. The FPU control word is set to 037FH (round to nearest, all exceptions
masked, 64-bit precision). The status word is cleared (no exception flags set, TOP is set
to 0). The data registers in the register stack are left unchanged, but they are all
tagged as empty (11B). Both the instruction and data pointers are cleared.
The FINIT instruction checks for and handles any pending unmasked floating-point
exceptions before performing the initialization; the FNINIT instruction does not.
Operation
FPUControlWord  037FH;
FPUStatusWord  0;
FPUTagWord  FFFFH;
FPUDataPointer  0;
FPUInstructionPointer  0;
FPULastInstructionOpcode  0;
FPU Flags Affected
C0, C1, C2, C3 cleared to 0.
Floating-point Exceptions
None.
Additional Itanium System Environment Exceptions
Itanium Reg Faults Disabled FP Register Fault if PSR.dfl is 1.
Protected Mode Exceptions
#NM
Real Address Mode Exceptions
#NM
Virtual 8086 Mode Exceptions
#NM
Volume 4: Base IA-32 Instruction Reference
Instruction Description
FINIT Initialize FPU after checking for pending unmasked
floating-point exceptions.
FNINIT Initialize FPU without checking for pending unmasked
floating-point exceptions.
EM or TS in CR0 is set.
EM or TS in CR0 is set.
EM or TS in CR0 is set.
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