REP              Repeat                              Flags: not altered
 
REP  string-instruction
 
          Logic:    while CX <> 0                      ;for MOVS, LODS or STOS
                        execute string instruction
                        CX  CX - 1
                   ------------------------------------------
                    while CX <> 0
                        execute string instruction     ;for CMPS or SCAS
                        CX  CX - 1
                        if ZF = 0 terminate loop
 
    REP is a prefix that may be specified before any string instruction
    (CMPS, LODS, MOVS, SCAS, and STOS). REP causes the string instruction
    following it to be repeated, as long as CX does not equal 0; CX is
    decremented after each execution of the string instruction.  (For CMPS
    and SCAS, REP will also terminate the loop if the Zero Flag is clear
    after the string instruction executes.)
 
  --------------------------------------------------------------------------
   Operands                  Clocks   Transfers  Bytes   Example
      -                        2          -        1     REP MOVS TO,FROM
  --------------------------------------------------------------------------
 
       Notes:         If CX is initially 0, the REPeated instruction is
                      skipped entirely.
 
                      The test for CX equal to 0 is performed before the
                      instruction is executed.  The test for the Zero Flag
                      clear--done only for CMPS and SCAS--is performed
                      after the instruction is executed.
 
                      REP, REPE (Repeat While Equal), and REPZ (Repeat
                      While Zero) are all synonyms for the same
                      instruction.
 
                      REPNZ (Repeat Not Zero) is similar to REP, but when
                      used with CMPS and SCAS, will terminate with the
                      Zero Flag set, rather than cleared.
 
                      REP is generally used with the MOVS (Move String)
                      and STOS (Store String) instructions; it can be
                      thought of as "repeat while not end of string."
 
                      You do not need to initialize ZF before using
                      repeated string instructions.
 
                      A REPeated instruction that is interrupted between
                      repeats will correctly resume processing upon return
                      from the interrupt. However, if other prefixes are
                      used on a single instruction (for example, segment
                      override or LOCK) in addition to the REP, all
                      prefixes except the one that immediately preceded
                      the string instruction will be lost. Therefore, if
                      you must use more than one prefix on a single
                      instruction, you should disable interrupts before
                      the instruction, and enable them afterwards. Note
                      that even this precaution will not prevent a non-
                      maskable interrupt, and that lengthy string
                      operations may cause large delays in interrupt
                      processing.
 
  -------------------------------- Example ---------------------------------
 
    The following example moves 100 bytes from BUFFER1 to BUFFER2:
 
          CLD                     ;Move in the forward direction
          LEA     SI, BUFFER1     ;Source pointer to SI
          LEA     DI, BUFFER2     ;  ...and destination to DI
          MOV     CX,100          ;REP uses CX as the counter
          REP     MOVSB           ;  ...and do it

Seealso:


 REPNE 
 MOVS 
 STOS 
 CMPS 
 SCAS 
 LODS 
 CLD 
 STD