Please title this page. (32bb-eg.htm)

PIC Microcontoller Subtraction Math Method

32 bit unsigned substraction from Eddy Gora

;------------------------------------------------------------------------ ; This is simple routine for full unsigned 32 bit substract ; a - b and result back in a ( initially a is lost ) ; on exit success, CARRY = 0, on fail ( substraction negative ) CARRY = 1 ; can be easly reduced / increased for 8 / 16 / 32 / 64 bits ; no optimisations ( tricks ) are made ; enjoy, eddy@hcv.ro from HCV Grup Ltd., __Config 3FF1h include <p16f877a.inc> a1 equ 0x20 a2 equ 0x21 a3 equ 0x22 a4 equ 0x23 b1 equ 0x24 b2 equ 0x25 b3 equ 0x26 b4 equ 0x27 org 0 START clrf a1 clrf a2 clrf a3 clrf a4 clrf b1 clrf b2 clrf b3 clrf b4 movlw 0x9c movwf a1 movlw 0x00 movwf a2 movlw 0x00 movwf a3 movlw 0xE2 movwf a4 ; MSB movlw 0x9d movwf b1 movlw 0xff movwf b2 movlw 0x4f movwf b3 movlw 0xc0 movwf b4 ; MSB nop call SUBB_32 nop SELF goto SELF ;------------------------------------------------------------------------ ; This is simple routine for full unsigned 32 bit substract ; a - b and result back in a ( initially a is lost ) ; on exit success, CARRY = 0, on fail ( substraction negative ) CARRY = 1 ; can be easly reduced / increased for 8 / 16 / 32 / 64 bits ; no optimisations ( tricks ) are made ; enjoy, eddy@hcv.ro from HCV Grup Ltd., SUBB_32 bcf STATUS,C ; clear our routine return flag movf b1,W ; substract first LSB bytes subwf a1,F ; a1 - b1 --> a1 ; a > b --> c=1 ; a = b --> c=1 ; a < b --> c=0 we have BORROW btfsc STATUS,C ; have BORROW ? goto NO_BORROW1 ; 1 NO ; 0 YES, so substract 1 from the next LSB movlw .1 subwf a2,F btfsc STATUS,C ; have also BORROW here ? goto NO_BORROW1 ; 1 ; 0 YES, so substract more, 1 from next movlw .1 subwf a3,F btfsc STATUS,C ; still BORROW ? goto NO_BORROW1 ; 1 ; 0 YES, substract 1 from the last movlw .1 subwf a4,F btfsc STATUS,C goto NO_BORROW1 bsf STATUS,C ; if another BORROW, the substraction result is negative ; so return quick with CARRY = 1 return NO_BORROW1 movf b2,w ; the same manner ... subwf a2,f btfsc STATUS,C goto NO_BORROW2 movlw .1 subwf a3,F btfsc STATUS,C goto NO_BORROW2 movlw .1 subwf a4,F btfsc STATUS,C goto NO_BORROW2 bsf STATUS,C return NO_BORROW2 movf b3,w subwf a3,f btfsc STATUS,C goto NO_BORROW3 movlw .1 subwf a4,F btfsc STATUS,C goto NO_BORROW3 bsf STATUS,C return NO_BORROW3 movf b4,w subwf a4,f btfsc STATUS,C goto NO_BORROW4 bsf STATUS,C return NO_BORROW4 bcf STATUS,C return ;----------------------------------------------------------------------- end

file: /Techref/microchip/math/sub/32bb-eg.htm, 4KB, , updated: 2009/2/13 15:12, local time: 2024/12/26 07:57,

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