> I hate C too, so here is my code:
>
> ; Xvar=Xvar*2+1
> movf      Xvar,w        ;put X in W
> addwf    Xvar,f          ; add W to X (X*2)
> incf        Xvar,f          ; add 1 (x*2+1)
>
> Note that the result is modulo 256 so it's working only if  X<127. Thus
you
> can check the C flag for overfolw and use it also for X>127

The other methods do this too.  There is no need for a third instruction:

     bsf   status, c     ;set value of bit to shift in
     rlf   x             ;shift left (X*2), shift in 1 (X*2 + 1)

Or:

     rlf   x             ;shift left (X*2), garbage in low bit
     bsf   x, 0          ;explicitly set low bit for the added 1

Either way the C flag is set if an overflow occurred, since a 1 bit would
have been shifted out by the RLF instruction.


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