Here's a divide-by-3 routine that my son Paul (fmdesignpe@aol.com)
reminded me of when I
admitted I couldn't remember.  It's not fast, but is real simple to
understand, and can easily be
generalized to divide by any integer.

    Number (unsigned byte) to divide in X.  Scratch files L (little) and B
(big), both initialized to 0.
Loop    add 3 to B
        is B greater than X ?
        if so: we're done, with answer in L
        if not: add 1 to L and go to Loop

    We're filling B three times as fast as we are L, so when B exceeds X, L is
one third of X.
Here's the code:

btst    movlw   3
        addwf   B,F             ;add 3 to B
        movf    B,W
        subwf   X,W             ;compare B to X
        btfss   STATUS,C        ;if Carry set, B <= X, so increment L and loop
        goto    done            ;if not, we're done
        incf    L,F             ;add 1 to L
        goto    btst            ;  and loop again
done    ;result is in L

    Works with any divisor.  To divide by 13, just change the first
instruction to "movlw  13".

-- Mel Evans    mevans1027@aol.com    813/595-7685