> > Hmm... my attempt:
> >
>
> Interesting - same number of instructions, but avoids using the temp
> location, but does require the known-zero, which not all PICs have.

It's true that not all PICs have a hardware known-zero.  Nonetheless, you
might want to consider having the compiler allocate one.  You could use
the same location to hold things like the loop counter for shifting oper-
ations, the byte counter for structure copying, etc. if you ensured that
it was always zero in the "general" context.  In fact, having a loop counter
which is always zero when not in a loop can be useful if your loops have
power-of-two repetition counts (e.g. rather than saying:

        movlw   8
        movwf   KZloop
loop
        ...
        decfsz  KZloop
         goto   loop

you could replace the first two instructions with:

        bsf     KZloop,3

Note that in addition to the "rrf kz,w" instruction used to read C into the
MSB of W, there is also a very useful "rlf KZ,w" which is very nice when
doing arithmetic:

        movf    SourceL,w
        addwf   DestL,w
        rlf     KZ,w
        addwf   SourceH,w
        addwf   DestH,w

Note that the carry out of that instruction sequence won't be valid, but the
trick can be used for the high byte of any multi-byte addition (not generally
useful for subtraction, though).  While it "only" saves one cycle per add-
ition, 16-bit additions are probably one of the more common things people will
be doing.

By the way, it's possible to do a 3-cycle add-constant-with-propagating-carry:

        ; If const == 0, use this
        rlf     KZ,w
        addwf   dest
        ; If const != 255 use this:
        rlf     KZ,w
        addlw   const
        addwf   dest

        ; If const == 255, use this:
        movlw   255
        btfss   C
         addwf  dest

All of these lend themselves well to dest=src+const constructs:

        ; If const == 0, use this
        rlf     KZ,w
        addwf   src,w
        movwf   dest

        ; If const != 255, use this
        rlf     KZ,w
        addlw   const
        addwf   src,w
        movwf   dest

        ; If const == 255, use this
        movf    source,w
        btfss   C
         addlw  255
        movwf   dest

I don't think it's possible to do better than those.