PIC Microcontoller Math Method

BCD (packed) subtraction

From: Tony Nixon

;       ------------------------------------------
; SUBROUTINE - 24 BIT DIVISION
; numerator:        nratorH  nratorM  nratorL
; denominator:      denomH   denomM   denomL
;
; result:           nratorH  nratorM  nratorL
; remainder:        remainH  remainM  remainL
;
divizn  movlw .24
        movwf BCount
        movf nratorH,w
        movwf shiftH
        movf nratorM,w
        movwf shiftM
        movf nratorL,w
        movwf shiftL
        clrf nratorH
        clrf nratorM
        clrf nratorL
        ;
        clrf remainH
        clrf remainM
        clrf remainL
dloop   bcf status,carry
        rlf shiftL
        rlf shiftM
        rlf shiftH
        rlf remainL
        rlf remainM
        rlf remainH
        movf denomH,w
        subwf remainH,w
        btfss status,z
        goto nochk
        ;
        movf denomM,w
        subwf remainM,w
        btfss status,z
        goto nochk
        ;
        movf denomL,w
        subwf remainL,w
nochk   btfss status,carry
        goto nogo
        ;
        movf denomL,w
        subwf remainL
        btfss status,carry
        decf remainM
        movf remainM,w
        xorlw 0xff
        btfsc status,z
        decf remainH
        movf denomM,w
        subwf remainM
        btfss status,carry
        decf remainH
        movf denomH,w
        subwf remainH
        bsf status,carry
nogo    rlf nratorL
        rlf nratorM
        rlf nratorH
        decfsz BCount
        goto dloop
        ;
        return


Thanks Fred... I posted your version under Tony's... 

I wish I had time to test and debug all the code on the site, but I simply 
can't.. I depend on people like you who find problems, fix them and share 
the result.

In short: THANK YOU! <GRIN>

---
James Newton, webhost piclist.com (former Admin #3)
jamesnewton at piclist,com 1-619-652-0593 fax:1-208-279-8767
PIC/PICList FAQ: http://www.piclist.com or .org 

-----Original Message-----
From: Fred Maher [mailto: FREDFMAH at terra,es]
Sent: Saturday, September 28, 2002 10:59 PM
To: webmaster at piclist,com
Subject: I need someone to help me with:24/24

Dear webmaster,

Looking for a routine that works.....

In the PIC list , the only one  I could get working and that produced a 
useable result was Tony Nixons....

Even so it needed tweaking

First compile with MPLAB gave  more than 30 errors plus warnings.

1 Things  not defined initially
2  default warnings
3 Errors like status should be STATUS

   These are the things that leave us newbies on  the floor.

Having said all this this code is quite quick and the ONLY ONE that is easy 
to get working in the PICLIST  !!!!!!!!!!!!!!


The  tweaked code follows:---------------------------------------



;--------------------------------------------------------------------- 

;-------                 HEADER                ----------
;---------------------------------------------------------------------
;   FredMaher    Madrid  30 Sept 02  fredfmah@terra.es
;   Tony Newton's 24÷24  routine with worked example
;                      LCD MESSAGES
; position at beginning of 1st line col 0  movlw H'80
; position at beginning of second line     movlw H'C0'


       LIST P=16F628           ;  16F628 Runs at 20 MHz
       INCLUDE "p16F628.inc"

       __CONFIG    _CP_OFF & _WDT_OFF & _HS_OSC & _PWRTE_ON & _LVP_OFF & 
_BODEN_OFF

       ERRORLEVEL -224        ;  suppress annoying message because of tris
       ERRORLEVEL -302        ;  suppress message because of page change

  ;__FUSES _PWRTE_ON & _CP_OFF & _WDT_ON & _HS_OSC & _LVP_OFF & _MCLRE_OFF 
& _BODEN_OFF




; Define Information
      #DEFINE RS PORTA, 2
      #DEFINE E  PORTA, 3
     ;#DEFINE TOGGLESW PORTB, 6  ; not used at the moment
     ;#DEFINE LED PORTB, 5

;  Macro
Bank0 macro
	bcf STATUS, RP0   ;Select memory bank 0
	bcf STATUS, RP1
	endm

Bank1 macro
	bsf STATUS, RP0   ;Select memory bank 1
	bcf STATUS, RP1
	endm


;---------------------------------------------------------------
             CBLOCK 20H   ; from 20C to 7F = 67  ;Note. Careful with memory 
pages
;                                                      until you get some 
practice.
;---------------------------------------------------------------

;                   MATH ROUTINES
  ;                   24 / 24 Div --> 24

    ; TONY NIXON's Algorithm starts here + my retouching

; SUBROUTINE - 24 BIT DIVISION
; numerator:        nratorH  nratorM  nratorL
; denominator:      denomH   denomM   denomL
;
; result:           nratorH  nratorM  nratorL
; remainder:        remainH  remainM  remainL
nratorH
nratorM
nratorL
denomH
denomM
denomL
remainH
remainM
remainL
shiftH
shiftM
shiftL
BCount


;-------------------------------------------------------------------
        ENDC     ; end of definition block
;-------------------------------------------------------------------




    ORG 0        ; start at location 0
    goto Main    ; jump over to main routine

Main:
    call      Div24
Homesweethome:
    nop
    goto Homesweethome


Div24:

; Example  1000000/16960 = F4240 / 4240  =58.962 ( remainder... 
remain/denom gives the decimal correctly... = Dec 0.962)



  	movlw 0x0F ; using Tony's notation
	movwf nratorH
  	movlw 0x42
	movwf nratorM
  	movlw 0x40
	movwf nratorL
  	movlw 0x00
	movwf denomH
  	movlw 0x42
	movwf denomM
  	movlw 0x40
	movwf denomL


divizn  movlw .24
         movwf BCount
         movf nratorH,w
         movwf shiftH
         movf nratorM,w
         movwf shiftM
         movf nratorL,w
         movwf shiftL
         clrf nratorH
         clrf nratorM
         clrf nratorL
         ;
         clrf remainH
         clrf remainM
         clrf remainL
dloop   bcf STATUS,C
         rlf shiftL,f
         rlf shiftM,f
         rlf shiftH,f
         rlf remainL,f
         rlf remainM,f
         rlf remainH,f
         movf denomH,w
         subwf remainH,w
         btfss STATUS,Z
         goto nochk
         ;
         movf denomM,w
         subwf remainM,w
         btfss STATUS,Z
         goto nochk
         ;
         movf denomL,w
         subwf remainL,w
nochk   btfss STATUS,C
         goto nogo
         ;
         movf denomL,w
         subwf remainL,f
         btfss STATUS,C
         decf remainM,f
         movf remainM,w
         xorlw 0xff
         btfsc STATUS,Z
         decf remainH,f
         movf denomM,w
         subwf remainM,f
         btfss STATUS,C
         decf remainH,f
         movf denomH,w
         subwf remainH,f
         bsf STATUS,C
nogo:
         rlf nratorL,f
         rlf nratorM,f
         rlf nratorH,f
         decfsz BCount,f
         goto dloop
         ;




	              Return

      end
;---------------------------------------------------------------------------------------------------------------------------------
;                                  End of 24/24 division routine by Tony Nixon
;----------------------------------------------------------------------------------------------------------------------------------

Cheers
Fred Maher
Madrid Spain

Code:

• -Remove-programsetcSPAM at netscape.net shares this code:

  Correcting High byte remainder error and added comments to Tony Nixon Code and Fred Mahers update to the 24bit by 24bit divide routine.   Thank you all for the USEFUL Code references and comments here. note Nikolai Golovchenko and Zet P.
  Fred Finster 3/15/2005     Error                       Corrected
  Numerator   Denominator   Remainder   Answer  Divisor  Remainder
  FFFFFF    FFFFFE           FF0001      000001 FFFFFE   000001
  8FFFFF    8FFFFE           FF0001      000001 8FFFFE   000001    
  2FFFFF    2FFFFE           FF0001      000001 2FFFFE   000001
  2FFFFE    2FFFFE                       000001 2FFFFE   000000
  2FFFFD    2FFFFE                       000000 2FFFFE   2FFFFD
  0F4240    004240                       00003A 004240   003FC0 
  ;-----------------------------------------------------
  ;   Here is the changed code, that corrects the HIGH byte remainder error
  ;     btfsc    STATUS, C       ; Carry Set? Then execute fixup code for when a borrow is generated
  ;      goto 		nodec_remainM   ; when no borrow bit is needed from the higher byte positions.
  ;
  ;
  ;--------------------------------------------------------------------
  ; SUBROUTINE - 24 BIT DIVISION  from  TONY NIXON
  ; numerator:        nratorH  nratorM  nratorL
  ; denominator:      denomH   denomM   denomL
  ;
  ; result:           nratorH  nratorM  nratorL
  ; remainder:        remainH  remainM  remainL
  ;
  Divide_24x24:
        movlw    .24		; set decimal 24 loop count
        movwf    BCount
        movf     nratorH,w ; copy Numerator into Shift Holding ram registers
        movwf    shiftH
        movf     nratorM,w
        movwf    shiftM
        movf     nratorL,w
        movwf    shiftL
        clrf     nratorH	;  clear final Answer Numerator Ram locations
        clrf     nratorM
        clrf     nratorL
        ;
        clrf     remainH  ;  clear final Answer Remainder Ram locations
        clrf     remainM
        clrf     remainL
  dloop:
        bcf		STATUS, C  ; bit clear Carry Flag in STATUS register
        rlf		shiftL, f  ; Shift numerator(dividend) Left to move
        rlf		shiftM, f  ; next bit to remainder
        rlf		shiftH, f  ; and shift in next bit of result
  
        rlf		remainL, f ; shift carry (next Dividend bit) into remainder
        rlf		remainM, f
        rlf		remainH, f
        movf     denomH,w
        subwf    remainH,w  ; subtract divsor(denomH) from(newly shifted left) Remainder HIGH byte.
        btfss    STATUS, Z
        goto     nochk		  ; skip if result was ZERO from good subtraction result
        ;
        movf     denomM,w
        subwf    remainM,w  ; subtract divsor(denomM) from(newly shifted left) Remainder MIDDLE byte.
        btfss    STATUS, Z
        goto     nochk		  ; skip if result was ZERO from good subtraction result
        ;
        movf     denomL,w
        subwf    remainL,w  ; subtract divsor(denomL) from(newly shifted left) Remainder LOW byte.
  nochk:
        btfss    STATUS, C   ;  Carry SET? then denom is larger than reemainder
        goto     nogo
        ;
        movf     denomL,w			 
        subwf    remainL, f   	 ; Subtract denominator from remainder value in Low Byte
        btfsc    STATUS, C       ; Carry Set? Then execute fixup code for when a borrow is generated
        goto 		nodec_remainM   ; when no borrow bit is needed from the higher byte positions.
        decf     remainM, f      ; Decrement to Borrow from Middle Byte, because carry was SET.
        movf     remainM,w
        xorlw    0xff				 ; Check if rollover from Borrow occurred. remainM value went from 0 to 0xFF 
        btfsc    STATUS, Z
        decf     remainH, f		 ; ZERO bit set, yes rollover, so Decrement to Borrow from High Byte, too!
  nodec_remainM:
        movf     denomM,w
        subwf    remainM, f		 ; Subtract denominator from remainder value in Middle Byte
        btfss    STATUS, C
        decf     remainH ,f      ; Decrement High Byte, to borrow 1 bit
        movf     denomH,w   		 
        subwf    remainH, f      ; Subtract denominator from remainder value in High Byte
        bsf		STATUS, C       ; set CARRY bit to rotate in Numerator Result next.
  nogo:
        rlf		nratorL, f  ; rotate Numerator result left 1 bit
        rlf		nratorM, f
        rlf		nratorH, f
        decfsz   BCount, f   ; decrement the Loop Bit Counter
        goto     dloop
        ;
        return  					; all done
  
  
  

  +