PIC Microcontoller Math Method

48 by 24 bit division by Andy Lee

Hi

I've made very good use of the code posted on your site so I'd like to give my thanks to the many contributers from whome I have learnt loads and who have save me a lot of time and head-scratching.

By way of thanks, I offer the following adaptation of Tony Nixons 24x24 bit division routine. I have expanded it to perform 48x24 bit division. While a little lardier than Nikolai Golovchenko's routine, it uses big-ended format (my preference) and provides a remainder (unfortunetly at the cost of a bit more ram). Anyway, I hope this may save someone a bit of time, as mine has been. Thanks all.

Code:

• allee at fastmail.co.uk shares this code:

  ;**************************************************************************
  ;Div4824U
  ;Inputs:
  ;	Dividend - Dividend:6	(0 - least significant!)
  ;	Divisor	 - Test:3	(0 - least significant!)
  ;Temporary:
  ;	Counter	 - Count
  ;	Shift	 - Shift:6
  ;Output:
  ;	Quotient - Dividend:6	(0 - least significant!)
  ;	Remainder- Rem:3	(0 - least significant!)
  ;
  ;Adaptation of 24x24 division by Tony Nixon with corrections
  ;by Frank Finster 3/15/2005.
  ;Code adapted by Andy Lee
  ;01-Sep-2006    Original version
  ;**************************************************************************
  
  Div4824U:
  ;---------------------------------------------------
  ; SUBROUTINE - 48 by 24 BIT DIVISION
  	movlw 48
  	movwf Count
  	movff Dividend+0, Shift+0
  	movff Dividend+1, Shift+1
  	movff Dividend+2, Shift+2
  	movff Dividend+3, Shift+3
  	movff Dividend+4, Shift+4
  	movff Dividend+5, Shift+5
  	clrf Dividend+0
  	clrf Dividend+1
  	clrf Dividend+2
  	clrf Dividend+3
  	clrf Dividend+4
  	clrf Dividend+5
  
  	clrf Rem+2
  	clrf Rem+1
  	clrf Rem+0
  dloop
  	bcf STATUS, C
  	rlcf Shift+0
  	rlcf Shift+1
  	rlcf Shift+2
  	rlcf Shift+3
  	rlcf Shift+4
  	rlcf Shift+5
  	rlcf Rem+0
  	rlcf Rem+1
  	rlcf Rem+2
  	movf Test+2, w
  	subwf Rem+2, w
  	btfss STATUS, Z
  		bra nochk
  
  	movf Test+1,w
  	subwf Rem+1,w
  	btfss STATUS, Z
  		bra nochk
  
  	movf Test+0,w
  	subwf Rem+0,w
  nochk
  	btfss STATUS, C
  		bra nogo
  
  	movf Test+0,w
  	subwf Rem+0
  	btfsc STATUS, C
  		bra	nodec_remainM
  	decf Rem+1, f
  	movf Rem+1, w
  	xorlw 0xff
  	btfsc STATUS, Z
  		decf Rem+2, f
  nodec_remainM
  	movf Test+1, w
  	subwf Rem+1, f
  	btfss STATUS, C
  		decf Rem+2, f
  	movf Test+2, w
  	subwf Rem+2, f
  	bsf STATUS, C
  nogo
  	rlcf Dividend+0
  	rlcf Dividend+1
  	rlcf Dividend+2
  	rlcf Dividend+3
  	rlcf Dividend+4
  	rlcf Dividend+5
  	decfsz Count, f
  		goto dloop
         return
  

Comments:

• hahaha make sure when you set Count, that 48 is in DECIMAL!!
  ...:( wasted so much time because the compiler defaulted to hex!

Lewis Paul Lineberger of Alternate Energies Says:

I've provided a version of this code that fixes an overflow error, illustrated by
0x34631A9FC / 0xDD39E9. Also, the code is provided for PIC12/PIC16 assembly. Thanks so much for the original work! See
http://www.piclist.com/techref/member/LPL-AEA-Z85/index.htm