This content has not been validated; it was AI-generated following the x86-64 ISA Documentation generation process to maintain high quality. However, as no human has verified this data, errors may exist. If the accuracy of this data is critical, please consult the Intel SDM. The model used to generate this is gemma4:31b

FLDCW

Loads the x87 floating-point control word from a specified memory location into the x87 control register.

The following table covers what the source and destinations can be.

DO NOT support LOCK

This instruction is only available in x86-64 compatibility mode. It is not supported in x86-64 64-bit mode.

The memory operand MUST be aligned to a word boundary to avoid potential performance penalties or alignment exceptions depending on the processor configuration. Writing an invalid value to the control word may result in unexpected floating-point precision or rounding behavior for subsequent x87 instructions.