Online HelpPC 2.10 Quick Reference Utility Copyright 1991 David Jurgens
REP - Repeat String Operation
Usage: REP
Modifies flags: None
Repeats execution of string instructions while CX != 0. After
each string operation, CX is decremented and the Zero Flag is
tested. The combination of a repeat prefix and a segment override
on CPU's before the 386 may result in errors if an interrupt occurs
before CX=0. The following code shows code that is susceptible to
this and how to avoid it:
again: rep movs byte ptr ES:[DI],ES:[SI] ; vulnerable instr.
jcxz next ; continue if REP successful
loop again ; interrupt goofed count
next:
Clocks Size
Operands 808x 286 386 486 Bytes
none 2 2 2 1
- see Instruction Timing REPE REPNE
[helppc.bosbyte.nl] rep