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

FYL2X

Computes $y = x \cdot \log_2(x)$ where $x$ is the value in the ST(0) register. The result replaces the value in ST(0).

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

DO NOT support LOCK

This instruction is only available in compatibility mode when operating in x86-64 architecture. It is a floating-point instruction that operates exclusively on the x87 FPU register stack.

The operand $x$ SHALL be a positive finite number. If $x$ is negative, NaN, or infinity, the instruction triggers #I. If $x$ is zero, the result is zero and no exception is triggered. The precision of the result is subject to the current FPU control word; if the result cannot be represented exactly, #P is triggered.