PIC Microcontoller Math Method

32 bit binary addition

From: Regulus Berdin

        movf    twofour0,w
        addwf   prod0,f

        movf    twofour1,w
        btfsc   STATUS,c
         incfsz twofour1,w
          addwf prod1,f

        movf    twofour2,w
        btfsc   STATUS,c
         incfsz twofour2,w
          addwf prod2,f

        movf    twofour3,w
        btfsc   STATUS,c
         incfsz twofour3,w
          addwf prod3,f

Comments:

• I thought incfsz doesn't affect the Z-flag?
  -but greaet algorithm!-

•                       twofour1 w   c z
                        255      ?   1 ?
  movf    twofour1,w   ;255      255 1 0
  btfsc   STATUS,c     ;do not skip
   incfsz twofour1,w   ;0        255 1 1
    addwf prod1,f      ;skipped > prod1 no changed
  

• Oh, I see incfsz performs the carry with W and if W carrys again on the increment then W=0 and hence no change.
  
  Very clever!

Questions: