Hi Scott. Nice approach and realization. ;)

Some debugging...

> ;
> ; Multiply x*y and produce a 16bit result. The high byte of the
> ;result is aliased with x.
> ;
>
> multiply
>      movf   x,w     ;; or save a cycle by letting the caller init. ;)
>
>      clrc
>      clrf   res_lo
>
>      btfsc  y,0
>       goto  l0
>
>      btfsc  y,1
>       goto  l1
>
>      btfsc  y,2
>       goto  l2
>
>      btfsc  y,3
>       goto  l3
>
>      btfsc  y,4
>       goto  l4
>
>      btfsc  y,5
>       goto  l5
>
>      btfsc  y,6
>       goto  l6
>
>      btfsc  y,7
>       goto  l7
>

        clrf    x       ;otherwise y==0 but x isn't


>      goto   l8      ;; or return
>
> l0   rrf    x,f
>      rrf    res_lo,f
>
>      btfsc  y,1
>       addwf x,w
>
> l1   rrf    x,f
>      rrf    res_lo,f
>
>      btfsc  y,2
>       addwf x,w
>
> l2   rrf    x,f
>      rrf    res_lo,f
>
>      btfsc  y,3
>       addwf x,w
>
> l3   rrf    x,f
>      rrf    res_lo,f
>
>      btfsc  y,4
>       addwf x,w
>
> l4   rrf    x,f
>      rrf    res_lo,f
>
>      btfsc  y,5
>       addwf x,w
>
> l5   rrf    x,f
>      rrf    res_lo,f
>
>      btfsc  y,6
>       addwf x,w
>
> l6   rrf    x,f
>      rrf    res_lo,f
>
>      btfsc  y,7
>       addwf x,w
>
> l7   rrf    x,f
>      rrf    res_lo,f
>
> l8   return