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View code
32 bits by 16 using 16 bits by 16
Author: Nikolai Golovchenko
This code was originally located @ http://www.piclist.com
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; x = 60*1e6/y
;
; x, x+1 - rpm
; y, y+1 - pulse width in 1 us units
;
FindRPM
clrf x
movlw 0x87
movwf x+1
movlw 0x93
movwf x+2
movlw 0x03
movwf x+3
goto div32by16to16
; uint16 x = uint32 x / uint16 y
;
; Input:
; x, x+1, x+2, x+3 - 32 bit unsigned integer dividend (x - lsb, x+3 - msb)
; y, y+1 - 16 bit unsigned integer divisor
; Output:
; x, x+1 - 16 bit unsigned integer quotient
; Temporary:
; counter
; temp - remainder extension
;
; Note: result must fit in 16 bits for routine to work
; correctly
div32by16to16
goto div16by16loopinit ;or just move the label
; uint16 x = uint16 x / uint16 y
;
; Input:
; x, x+1 - 16 bit unsigned integer dividend (x - lsb, x+1 - msb)
; y, y+1 - 16 bit unsigned integer divisor
; Output:
; x, x+1 - 16 bit unsigned integer quotient
; Temporary:
; counter
; x+2, x+3 - 16 bit remainder
; temp - remainder extension
; Size: 36 instructions
; Max timing: 6+16*(5+13+3)-1+2+2=345 cycles
div16by16
clrf x+2 ;clear
clrf x+3 ;remainder
div16by16loopinit
clrf temp ;clear remainder extension
movlw 16
movwf counter
setc ;first iteration will be subtraction
div16by16loop
;shift in next result bit and shift out next
;dividend bit to remainder
rlf x, f ;shift lsb
rlf x+1, f ;shift msb
rlf x+2, f
rlf x+3, f
rlf temp, f
movf y, w
btfss x, 0
goto div16by16add
;subtract divisor from remainder
subwf x+2, f
movf y+1, w
skpc
incfsz y+1, w
subwf x+3, f
movlw 1
skpc
subwf temp, f
goto div16by16next
div16by16add
;add divisor to remainder
addwf x+2, f
movf y+1, w
skpnc
incfsz y+1, w
addwf x+3, f
movlw 1
skpnc
addwf temp, f
div16by16next
;carry is next result bit
decfsz counter, f
goto div16by16loop
;shift in last bit
rlf x, f
rlf x+1, f
return |
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