Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 4 REV 2.3 Manual page 116

FCLEX/FNCLEX—Clear Exceptions
Opcode
9B DB E2
DB E2
Description
Clears the floating-point exception flags (PE, UE, OE, ZE, DE, and IE), the exception
summary status flag (ES), the stack fault flag (SF), and the busy flag (B) in the FPU
status word. The FCLEX instruction checks for and handles any pending unmasked
floating-point exceptions before clearing the exception flags; the FNCLEX instruction
does not.
Operation
FPUStatusWord[0..7]  0;
FPUStatusWord[15]  0;
FPU Flags Affected
The PE, UE, OE, ZE, DE, IE, ES, SF, and B flags in the FPU status word are cleared. The
C0, C1, C2, and C3 flags are undefined.
Floating-point Exceptions
None.
Additional Itanium System Environment Exceptions
Itanium Reg Faults Disabled FP Register Fault if PSR.dfl is 1, NaT Register Consumption
Protected Mode Exceptions
#NM
Real Address Mode Exceptions
#NM
Virtual 8086 Mode Exceptions
#NM
Volume 4: Base IA-32 Instruction Reference
Instruction Description
FCLEX Clear floating-point exception flags after checking for pending
unmasked floating-point exceptions.
FNCLEX Clear floating-point exception flags without checking for
pending unmasked floating-point exceptions.
Abort.
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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