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View code
48 by 24 bit
Author: Nikolai
This code was originally located @ http://www.piclist.com
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;****************************************************
;max time in loop: 26 cycles
DIVIDE_48by23
; Test for zero division
MOVF Divisor,W
IORWF Divisor+1,W
IORWF Divisor+2,W
BTFSC STATUS,Z
RETLW 0x00 ; divisor = zero, not possible to calculate return with zero in w
; prepare used variables
CLRF Temp
CLRF Temp+1
CLRF Temp+2
MOVLW D'48' ; initialize bit counter
MOVWF BitCount
setc
DIVIDE_LOOP_48by23
RLF Dividend+5,F
RLF Dividend+4,F
RLF Dividend+3,F
RLF Dividend+2,F
RLF Dividend+1,F
RLF Dividend,F
; shift in highest bit from dividend through carry in temp
RLF Temp+2,F
RLF Temp+1,F
RLF Temp,F
MOVF Divisor+2,W ; get LSB of divisor
btfss Dividend+5, 0
goto Div48by23_add
; subtract 23 bit divisor from 24 bit temp
SUBWF Temp+2,F ; subtract
MOVF Divisor+1,W ; get middle byte
SKPC ; if overflow ( from prev. subtraction )
INCFSZ Divisor+1,W ; incresase source
SUBWF Temp+1,F ; and subtract from dest.
MOVF Divisor,W ; get top byte
SKPC ; if overflow ( from prev. subtraction )
INCFSZ Divisor,W ; increase source
SUBWF Temp,F ; and subtract from dest.
GOTO DIVIDE_SKIP_48by23 ; carry was set, subtraction ok, continue with next bit
Div48by23_add
; result of subtraction was negative restore temp
ADDWF Temp+2,F ; add it to the lsb of temp
MOVF Divisor+1,W ; middle byte
BTFSC STATUS,C ; check carry for overflow from previous addition
INCFSZ Divisor+1,W ; if carry set we add 1 to the source
ADDWF Temp+1,F ; and add it if not zero in that case Product+Multipland=Product
MOVF Divisor,W ; MSB byte
BTFSC STATUS,C ; check carry for overflow from previous addition
INCFSZ Divisor,W
ADDWF Temp,F ; handle overflow
DIVIDE_SKIP_48by23
DECFSZ BitCount,F ; decrement loop counter
GOTO DIVIDE_LOOP_48by23 ; another run
; finally shift in the last carry
RLF Dividend+5,F
RLF Dividend+4,F
RLF Dividend+3,F
RLF Dividend+2,F
RLF Dividend+1,F
RLF Dividend,F
RETLW 0x01 ; done
;****************************************************
;max time in loop: 30 cycles
DIVIDE_48by24
; Test for zero division
MOVF Divisor,W
IORWF Divisor+1,W
IORWF Divisor+2,W
BTFSC STATUS,Z
RETLW 0x00 ; divisor = zero, not possible to calculate return with zero in w
; prepare used variables
CLRF Temp
CLRF Temp+1
CLRF Temp+2
clrf Temp2
MOVLW D'48' ; initialize bit counter
MOVWF BitCount
DIVIDE_LOOP_48by24
RLF Dividend+5,F
RLF Dividend+4,F
RLF Dividend+3,F
RLF Dividend+2,F
RLF Dividend+1,F
RLF Dividend,F
; shift in highest bit from dividend through carry in temp
RLF Temp+2,F
RLF Temp+1,F
RLF Temp,F
rlf Temp2, f
MOVF Divisor+2,W ; get LSB of divisor
btfsc Temp2, 7
goto Div48by24_add
; subtract 24 bit divisor from 24 bit temp
SUBWF Temp+2,F ; subtract
MOVF Divisor+1,W ; get middle byte
SKPC ; if overflow ( from prev.
subtraction )
INCFSZ Divisor+1,W ; incresase source
SUBWF Temp+1,F ; and subtract from dest.
MOVF Divisor,W ; get top byte
SKPC ; if overflow ( from prev.
subtraction )
INCFSZ Divisor,W ; increase source
SUBWF Temp,F ; and subtract from dest.
movlw 1
skpc
subwf Temp2, f
GOTO DIVIDE_SKIP_48by24 ; carry was set, subtraction ok, continue with next bit
Div48by24_add
; result of subtraction was negative restore temp
ADDWF Temp+2,F ; add it to the lsb of temp
MOVF Divisor+1,W ; middle byte
BTFSC STATUS,C ; check carry for overflow from previous addition
INCFSZ Divisor+1,W ; if carry set we add 1 to the source
ADDWF Temp+1,F ; and add it if not zero in that case Product+Multipland=Product
MOVF Divisor,W ; MSB byte
BTFSC STATUS,C ; check carry for overflow from previous addition
INCFSZ Divisor,W
ADDWF Temp,F ; handle overflow
movlw 1
skpnc
addwf Temp2, f
DIVIDE_SKIP_48by24
DECFSZ BitCount,F ; decrement loop counter
GOTO DIVIDE_LOOP_48by24 ; another run
; finally shift in the last carry
RLF Dividend+5,F
RLF Dividend+4,F
RLF Dividend+3,F
RLF Dividend+2,F
RLF Dividend+1,F
RLF Dividend,F
RETLW 0x01 ; done
;**************************************************** |
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