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

                                Clocks                 Size
       Operands         808x  286   386   486          Bytes

       none              2     2     2                   1

       - see Instruction Timing   REPE   REPNE

Esc or Alt-X to exit rep Home/PgUp/PgDn/End ←↑↓→
Converted to HTML in 2006 by Timo Bingmann