| <<< LOOP Loop until CX/ECX = 0 | Index | LOOPZ/LOOPE Loop While CX/ECX > 0 and ZF = 1 >>> |
O D I T S Z A P C OF: Overflow flag TF: Trap flag AF: Aux carry
F F F F F F F F F DF: Direction flag SF: Sign flag PF: Parity flag
<none> IF: Interrupt flag ZF: Zero flag CF: Carry flag
LOOPNZ and LOOPNE are synonyms and generate identical opcodes. Like LOOP, they use either CX or ECX depending on the BITS setting and hence the mode. LOOPNZ/LOOPNE decrements CX and jumps to the location specified in the target operand if CX is not 0 and the Zero flag ZF is 0. Otherwise, execution falls through to the next instruction.
What this means is that the loop is pretty much controlled by ZF. If ZF remains 0, the loop is looped until CX is decremented to 0. But as soon as ZF is set to 1, the loop terminates. Think of it as "Loop While Not Zero Flag."
Keep in mind that LOOPNZ does not itself affect ZF. Some instruction within the loop (typically one of the string instructions) must do something to affect ZF to terminate the loop before CX/ECX counts down to 0.
r8 = AL AH BL BH CL CH DL DH r16 = AX BX CX DX BP SP SI DI
sr = CS DS SS ES FS GS r32 = EAX EBX ECX EDX EBP ESP ESI EDI
m8 = 8-bit memory data m16 = 16-bit memory data
m32 = 32-bit memory data i8 = 8-bit immediate data
i16 = 16-bit immediate data i32 = 32-bit immediate data
d8 = 8-bit signed displacement d16 = 16-bit signed displacement
d32 = 32-bit unsigned displacement
| <<< LOOP Loop until CX/ECX = 0 | Index | LOOPZ/LOOPE Loop While CX/ECX > 0 and ZF = 1 >>> |