X86 rep instruction

repnz scasb
rep assembly
cmpsb
weird x86 instructionsrep stosd
assembly rep instruction
x86 rep nop
x64 rep

x86 Instruction Set Reference. REP/REPE/REPZ/REPNE/REPNZ F3 6C, REP INS m8, DX, Input (E)CX bytes from port DX into ES:[(E)DI]. F3 6D, REP INS m16, DX Opcode, Instruction, Op/En, 64-Bit Mode, Compat/Leg Mode, Description. F3 6C, REP INS m8, DX, ZO, Valid, Valid, Input (E)CX bytes from port DX into There's a whole blog named after this instruction. And the first post describes the reason behind it: repzret.org/p/repzret/. REP - Repeat String Operation Usage: REP Modifies flags: None Repeats execution of string instructions while CX != 0. After each string operation, REP repeats instruction the number of times specified by iteration count ECX. REPE and REPNE prefixes allow to terminate loop on the value of ZF CPU flag. Each prefix causes the associated string instruction to repeat until the count register (CX) or the zero flag (ZF) matches a tested condition. REP/REPE/REPZ/REPNE/REPNZ -- Repeat Following String Operation. Opcode, Instruction, Clocks, Description, Example. F3 6C, rep insb, 13+6*(E)CX, Repetition prefixes are meaningful only when preceding string instructions. They cause the specified instruction to repeat as long as certain conditions are met