BSR - Bit Scan Reverse (386+ only)

	Usage:	BSR	dest,src
	Modifies flags: ZF


	Scans source operand for first bit set.  Sets ZF if a bit is found
	set and loads the destination with an index to first set bit.  Clears
	ZF is no bits are found set.  BSF scans forward across bit pattern
	(0-n) while BSR scans in reverse (n-0).


				 Clocks			Size
	Operands	 808x  286   386   486		Bytes

	reg,reg 	  -	-   10+3n  6-103	  3
	reg,mem 	  -	-   10+3n  7-104	 3-7
	reg32,reg32	  -	-   10+3n  6-103	 3-7
	reg32,mem32	  -	-   10+3n  7-104	 3-7


	- see Instruction Timing