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REPE

Repeats the CMPS instruction while the Zero Flag (ZF) is set and the RCX register is non-zero. After each iteration, RCX is decremented and the source and destination pointers are incremented or decremented based on the Direction Flag (DF). The operation terminates when ZF is cleared or RCX reaches zero.

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

Support LOCK

This instruction is available in 64-bit mode, compatibility mode, and 32-bit protected mode. The operand size is determined by the address prefix or the default operand size of the current mode.

If RCX is initialized to 0, the instruction does not execute any iterations and the pointers remain unchanged. To ensure the instruction processes at least one element, the programmer MUST ensure RCX is greater than 0. Failure to handle the RCX = 0 case may lead to unexpected logic flow in comparison loops.