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View code
16 bits by 8 with result as fraction
Author: Nikolai Golovchenko
This code was originally located @ http://www.piclist.com
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;Division of 16bit by 8 bit with a result in Q16.16 form
;
; X_Int.X_Frac = X_Int / Y
;
; RAM - 6 bytes (1 temp):
; X_Int = X_IntH:X_IntL 16 bit input/ output integer part
; X_Frac = X_FracH:X_FracL 16 bit output fractional part
; Y divisor / temporary
; Counter counter
;
; Size = 39 instructions
; Execution time = 6+16*14-1+3+16*14-1+3+2(return)
; = 460 instruction cycles
;
; 8-July-2000 by Nikolai Golovchenko
; 16-February-2001 fixed, reduced execution time and temporaries
Div16by8to16_16
clrf X_FracL
clrf X_FracH
movlw 16
movwf Counter
movf Y, w ;keep Y value in accumulator
clrf Y ;and use Y register as temporary
;Find integer part
Div16by8to16_16a
rlf X_IntL, f ;shift next msb into temporary
rlf X_IntH, f
rlf Y, f
rlf Counter, f ;carry has 9th bit of temporary
;copy carry to counter
subwf Y, f ;substract Y (in w) from temporary
skpnc ;if no borrow, set Counter.0
bsf Counter, 0
btfss Counter, 0 ;if Counter.0 clear (borrow) restore temporary
addwf Y, f
clrc ;restore counter
rrf Counter, f
;at this point carry is the next bit of result
decfsz Counter, f ;repeat 16 times to find integer part
goto Div16by8to16_16a
;shift last integer bit
rlf X_IntL, f
rlf X_IntH, f
;Find fractional part
bsf Counter, 4 ;Counter = 16
Div16by8to16_16b
;Shift zero bit into temporary
rlf X_FracL, f
rlf X_FracH, f
rlf Y, f
rlf Counter, f ;carry has 9th bit of temporary
;copy carry to counter
subwf Y, f ;substract Y(in w) from temporary
skpnc ;if no borrow, set Counter.0
bsf Counter, 0
btfss Counter, 0 ;if Counter.0 clear (borrow) restore temporary
addwf Y, f
clrc ;restore counter
rrf Counter, f
decfsz Counter, f ;repeat 16 times
goto Div16by8to16_16b
;shift last fractional bit
rlf X_FracL, f
rlf X_FracH, f
movwf Y ;restore divisor
return |
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