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AESKEYGENASSIST

AESKEYGENASSIST performs the key expansion assistance operation for the AES algorithm. It takes an input value, applies a specific transformation involving a rotation, a substitution via the S-box, and a XOR operation with a round constant, then stores the resulting value in the destination.

The table after the description covers what the source and destinations can be.

DO NOT support LOCK

This instruction is only available if the processor supports the AES-NI instruction set. It operates exclusively on XMM registers; it is NOT supported for memory operands or general-purpose registers.

The instruction requires the processor to be in 64-bit mode or compatibility mode. Users MUST ensure that the AES-NI feature flag is enabled in the CPUID to avoid an #UD (Undefined Instruction) exception. Since this instruction modifies the destination register, the original input value is lost unless previously backed up to another register or memory.