3-605
INSTRUCTION SET REFERENCE
REP/REPE/REPZ/REPNE
/REPNZRepeat String Operation Prefix
Description
These instructions repeat a string instruction the number of times specified in the count register
((E)CX) or until the indicated condition of the ZF flag is no longer met. The REP (repeat), REPE
(repeat while equal), REPNE (repeat while not equal), REPZ (repeat while zero), and REPNZ
(repeat while not zero) mnemonics are prefixes that can be added to one of the string instruc-
tions. The REP prefix can be added to the INS, OUTS, MOVS, LODS, and STOS instructions,
and the REPE, REPNE, REPZ, and REPNZ prefixes can be added to the CMPS and SCAS
instructions. (The REPZ and REPNZ prefixes are synonymous forms of the REPE and REPNE
prefixes, respectively.) The behavior of the REP prefix is undefined when used with non-string
instructions.
OpcodeInstruction
Description
F3 6C
REP INS r/m8, DX
Input (E)CX bytes from port DX into ES:[(E)DI]
F3 6D
REP INS r/m16,DX
Input (E)CX words from port DX into ES:[(E)DI]
F3 6D
REP INS r/m32,DX
Input (E)CX doublewords from port DX into ES:[(E)DI]
F3 A4
REP MOVS m8,m8
Move (E)CX bytes from DS:[(E)SI] to ES:[(E)DI]
F3 A5
REP MOVS m16,m16Move (E)CX words from DS:[(E)SI] to ES:[(E)DI]
F3 A5
REP MOVS m32,m32Move (E)CX doublewords from DS:[(E)SI] to ES:[(E)DI]
F3 6E
REP OUTS DX,r/m8Output (E)CX bytes from DS:[(E)SI] to port DX
F3 6F
REP OUTS DX,r/m16Output (E)CX words from DS:[(E)SI] to port DX
F3 6F
REP OUTS DX,r/m32Output (E)CX doublewords from DS:[(E)SI] to port DX
F3 AC
REP LODS AL
Load (E)CX bytes from DS:[(E)SI] to AL
F3 AD
REP LODS AX
Load (E)CX words from DS:[(E)SI] to AX
F3 AD
REP LODS EAX
Load (E)CX doublewords from DS:[(E)SI] to EAX
F3 AA
REP STOS m8
Fill (E)CX bytes at ES:[(E)DI] with AL
F3 AB
REP STOS m16
Fill (E)CX words at ES:[(E)DI] with AX
F3 AB
REP STOS m32
Fill (E)CX doublewords at ES:[(E)DI] with EAX
F3 A6
REPE CMPS m8,m8Find nonmatching bytes in ES:[(E)DI] and DS:[(E)SI]
F3 A7
REPE CMPS m16,m16Find nonmatching words in ES:[(E)DI] and DS:[(E)SI]
F3 A7
REPE CMPS m32,m32Find nonmatching doublewords in ES:[(E)DI] and DS:[(E)SI]
F3 AE
REPE SCAS m8
Find non-AL byte starting at ES:[(E)DI]
F3 AF
REPE SCAS m16
Find non-AX word starting at ES:[(E)DI]
F3 AF
REPE SCAS m32
Find non-EAX doubleword starting at ES:[(E)DI]
F2 A6
REPNE CMPS m8,m8Find matching bytes in ES:[(E)DI] and DS:[(E)SI]
F2 A7
REPNE CMPS m16,m16Find matching words in ES:[(E)DI] and DS:[(E)SI]
F2 A7
REPNE CMPS m32,m32Find matching doublewords in ES:[(E)DI] and DS:[(E)SI]
F2 AE
REPNE SCAS m8
Find AL, starting at ES:[(E)DI]
F2 AF
REPNE SCAS m16
Find AX, starting at ES:[(E)DI]
F2 AF
REPNE SCAS m32
Find EAX, starting at ES:[(E)DI]
