from Nikolai Golovchenko
;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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<A HREF="http://www.piclist.com/techref/microchip/math/div/16by8lzf-ng.htm"> PIC Microcontoller Math Method Division 16 bits by 8 with result as fraction rather than remainder </A>
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