CMPS - Compare String (Byte, Word or Doubleword)

	Usage:	CMPS	dest,src
		CMPSD	(386+ only)
	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)

	- see Instruction Timing