29.8.3.1. x86 REP prefix
Example: userland/arch/x86_64/rep.S
Repeat a string instruction RCX times:
As the repetitions happen:
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RCX decreases, until it reaches 0
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RDI and RSI increase
The variants: REPZ, REPNZ (alias REPE, REPNE) repeat a given instruction until something happens.
REP and REPZ also additionally stop if the comparison operation they repeat fails.
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REP: INS, OUTS, MOVS, LODS, and STOS
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REPZ: CMPS and SCAS