Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1422

FDECSTP—Decrement Stack-Top Pointer
Opcode
D9 F6
Description
Subtracts one from the TOP field of the FPU status word (decrements the top-of-stack
pointer). The contents of the FPU data registers and tag register are not affected.
Operation
IF TOP = 0
THEN TOP  7;
ELSE TOP  TOP - 1;
FI;
FPU Flags Affected
The C1 flag is set to 0; otherwise, cleared to 0. The C0, 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
4:120
Instruction Description
FDECSTP Decrement TOP field in FPU status word.
Abort.
EM or TS in CR0 is set.
EM or TS in CR0 is set.
EM or TS in CR0 is set.
Volume 4: Base IA-32 Instruction Reference