BSR - Bit Scan Reverse  (386+)

        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


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