Amey Deosthali <amey@vision.ece.utexas.edu> wrote:

> The 8x8 multiply routine given in application note AN526 by
> Microchip is optimized for speed. Still it takes a stagerring 44
> instructions in the worst case. Is this the best routine  for
> multiplication?

    That depends on your definition of "best", Amey.

> Is there any other routine available, requiring less number of
> instructions?

    Of course.  Try something like this:

        ; Enter with multiplier in W-Reg, multiplicand in "PRODLO".
        ; Exits with product in PRODHI:PRODLO.

        MPY8X8:

            CLRF    PRODHI

            CLRF    COUNT
            BSF     COUNT,3

            RRF     PRODLO

        LOOP:

            SKPNC
            ADDWF   PRODHI

            RRF     PRODHI
            RRF     PRODLO

            DECFSZ  COUNT
            GOTO    LOOP

    -Andy

    P.S.  As usual with code that I write online, this routine hasn't
          even been assembled, let alone tested.  Still, it's pretty
          simple; I'd be surprised if it didn't work.

=== Andrew Warren - fastfwd@ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499