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SCASW

Compares the value in the ax register with a word-sized value from the memory location pointed to by edi (in 32-bit mode) or rdi (in 64-bit mode). The zf flag is set if the operands are equal. After the comparison, the index register (edi or rdi) is incremented or decremented by 2, depending on the value of the df flag in the rflags register.

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

DO NOT support LOCK

This instruction is available in 64-bit mode and compatibility mode. It operates exclusively on 16-bit operands regardless of the current operating mode.

The df (Direction Flag) MUST be configured correctly before execution; if df is 0, the index register increments, and if df is 1, it decrements. Using this instruction with a rep prefix WILL continue the operation until zf is cleared or rcx reaches 0. Failure to initialize rcx with the correct count before a rep prefix WILL result in unintended memory accesses.