PIC Microcontoller Math Method

Two's complemnt of a 16 bit word (2 bytes)

        comf    var,f           ;Complement all bytes
        comf    var+1,f

        incf    var,f           ;Inc. low byte always
        skpnz                   ;Skip if no carry to higher bytes
        incf    var+1,f         ;Carry to next byte

Questions:

• Shouldn't the skpnz be skpnc? Ken R Helberg of Altec Lansing replies: incf doesn't affect the carry flag, so skpnz is correct.

Comments:

• If I'm not mistaken, the three last lines could be replaced with
  
  incfsz var,F
  incf var+1,F

Stef Says: " Increment of "var+1" must be done only if
incf var
result IS zero. So, incfsz will not work. "