SCAS - Scan String (Byte, Word or Doubleword)

	Usage:	SCAS	string
		SCASB
		SCASW
		SCASD	(386+ only)
	Modifies flags: AF CF OF PF SF ZF


	Compares value at ES:DI (even if operand is specified) from the
	accumulator and sets the flags similar to a subtraction.  DI is
	incremented/decremented based on the instruction format (or
	operand size) and the state of the Direction Flag.  Use with REP
	prefixes.

				 Clocks			Size
	Operands	 808x  286   386   486		Bytes

	string		  15	7     7	    6		  1  (W88=19)


	- see Instruction Timing