CMPS - Compare String (Byte, Word or Doubleword)

        Usage:  CMPS    dest,src
                CMPSD   (386+)
        Modifies flags: AF CF OF PF SF ZF

        Subtracts destination value from source without saving results.
        Updates flags based on the subtraction and  the index registers
        (E)SI and (E)DI are incremented or decremented depending on the
        state of the Direction Flag.  CMPSB inc/decrements the index
        registers by 1, CMPSW inc/decrements by 2, while CMPSD increments
        or decrements by 4.  The REP prefixes can be used to process
        entire data items.

                                 Clocks                 Size
        Operands         808x  286   386   486          Bytes

        dest,src          22    8     10    8             1  (W88=30)

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