Hi Dmitriy,

Something like this: (untested)

; Multi byte BCD increment
; by Regulus Berdin
;

INC:

  MOVLW  BCD_LSB
  MOVWF FSR
  MOVLW BCD_CNT
  MOVWF CNT

LOOP:

  MOVLW 67
  ADDWF INDF,F
  MOVLW -60
  SKPDC
   MOVLW -66
  SKPC
   ADDWF CNT,F

  SKPZ
   RETURN

  INCF FSR,F
   
  DECFSZ CNT,F
    GOTO LOOP

 RETURN


; Multi byte BCD decrement
; by Regulus Berdin
;

DECR:

  MOVLW  BCD_LSB
  MOVWF FSR
  MOVLW BCD_CNT
  MOVWF CNT

LOOP:

  MOVLW 0xFF
  ADDWF CNT,F
  MOVLW -6
  SKPC
   MOVLW -66
  SKPDC
   ADDWF CNT,F

  XORLW -0x66
  SKPZ
   RETURN

  INCF FSR,F
   
  DECFSZ CNT,F
    GOTO LOOP

 RETURN


Also have posted similar to this many years ago. I think it is also in
the archive but not on the piclist code repository.

regards,
Reggie


On 8/3/05, Dmitriy Kiryashov <vze27bym@verizon.net> wrote:
> Hi Reggie.
> 
> Nice logical approach indeed :)
> How would you cascade this approach
> if bcd number is several bytes sized ?
> 
> 
> WBR Dmitriy.
> 
> 
> 
> > I had posted this about 6 or 7 years ago. 7 cycles :) excluding return.
> > radix is HEX.
> >
> > BCD_INCR:
> >      MOVLW 67
> >      ADDWF CNT,F
> >      MOVLW -60
> >      SKPDC
> >       MOVLW -66
> >      SKPC
> >       ADDWF CNT,F
> >      RETURN
> >
> > BCD_DECR:
> >      MOVLW 0xFF
> >      ADDWF CNT,F
> >      MOVLW -6
> >      SKPC
> >       MOVLW -66
> >      SKPDC
> >       ADDWF CNT,F
> >      RETURN
> >
> > On BCD_INCR, Z flag is set when overflow occurs.
> > But on BCD_DECR, adding "XORLW -0x66" at the end will set Z flag during
> > an underflow.
> >
> > regards,
> > Reggie
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