Andrew Warren wrote:
>
>
> Here's this year's challenge:
>
>     Write a routine to multiply two numbers, each in the range
>     0-100... The numbers are in two registers, called SMALL and
>     LARGE, and your 16-bit result should be in two different
>     registers, called PROD_HI and PROD_LO.
>

<SNIP>

> I just wrote one that takes 34 cycles... I'm SURE someone can do
> better.

Just so you don't get the whole beer, here's one that's 34 cycles
too (and probably the same as yours).

        CLRF    PROD_HI
        CLRF    PROD_LO
        CLRC
        MOVF    LARGE,W

        BTFSC   SMALL,0
         ADDWF  PROD_HI,F
        RRF     PROD_HI,F
        RRF     PROD_LO,F

        BTFSC   SMALL,1
         ADDWF  PROD_HI,F
        RRF     PROD_HI,F
        RRF     PROD_LO,F

        BTFSC   SMALL,2
         ADDWF  PROD_HI,F
        RRF     PROD_HI,F
        RRF     PROD_LO,F

        BTFSC   SMALL,3
         ADDWF  PROD_HI,F
        RRF     PROD_HI,F
        RRF     PROD_LO,F

        BTFSC   SMALL,4
         ADDWF  PROD_HI,F
        RRF     PROD_HI,F
        RRF     PROD_LO,F

        BTFSC   SMALL,5
         ADDWF  PROD_HI,F
        RRF     PROD_HI,F
        RRF     PROD_LO,F

        BTFSC   SMALL,6
         ADDWF  PROD_HI,F
        RRF     PROD_HI,F
        RRF     PROD_LO,F

        RRF     PROD_HI,F
        RRF     PROD_LO,F

but... I'm quite certain there is a faster way.

Scott