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

FNINIT

Initializes the FPU by resetting the FPU control word, status word, and tag word to their default values.

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

DO NOT support LOCK

FNINIT is available in 64-bit mode, though the x87 FPU is primarily used for compatibility. It does not require any operands.

The instruction does not trigger any floating-point exceptions (#I, #Z, #D, #O, #U, #P). Since it resets the status word, any previously pending floating-point exceptions are cleared.