Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1443

FLDCW—Load Control Word
Opcode
D9 /5
Description
Loads the 16-bit source operand into the FPU control word. The source operand is a
memory location. This instruction is typically used to establish or change the FPU's
mode of operation.
If one or more exception flags are set in the FPU status word prior to loading a new FPU
control word and the new control word unmasks one or more of those exceptions, a
floating-point exception will be generated upon execution of the next floating-point
instruction (except for the no-wait floating-point instructions. To avoid raising
exceptions when changing FPU operating modes, clear any pending exceptions (using
the FCLEX or FNCLEX instruction) before loading the new control word.
Operation
FPUControlWord  SRC;
FPU Flags Affected
C0, C1, C2, C3 undefined.
Floating-point Exceptions
None; however, this operation might unmask a pending exception in the FPU status
word. That exception is then generated upon execution of the next waiting
floating-point instruction.
Additional Itanium System Environment Exceptions
Itanium Reg Faults Disabled FP Register Fault if PSR.dfl is 1.
Itanium Mem FaultsVHPT Data Fault, Nested TLB Fault, Data TLB Fault, Alternate Data
Protected Mode Exceptions
#GP(0)
#SS(0)
#NM
#PF(fault-code)
#AC(0)
Volume 4: Base IA-32 Instruction Reference
Instruction Description
FLDCW m2byte Load FPU control word from m2byte.
TLB Fault, Data Page Not Present Fault, Data NaT Page Consumption
Abort, Data Key Miss Fault, Data Key Permission Fault, Data Access
Rights Fault, Data Access Bit Fault, Data Dirty Bit Fault
If a memory operand effective address is outside the CS, DS, ES, FS,
or GS segment limit.
If the DS, ES, FS, or GS register is used to access memory and it
contains a null segment selector.
If a memory operand effective address is outside the SS segment
limit.
EM or TS in CR0 is set.
If a page fault occurs.
If alignment checking is enabled and an unaligned memory
reference is made while the current privilege level is 3.
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