base:8bit_divide_by_constant_8bit_result

# 8bit Divide by Constant — 8bit result

; Unsigned Integer Division Routines (rev 2) ; by Omegamatrix ; ; Rev 1 (June 14, 2014) ; Divide by 6,10,12,20,24,26, and 28 have all been replace with new and better routines. ; ; Rev 2 (June 21, 2014) ; Divide by 22 routines has been upgraded to one that saves 3 cycles, same amount of bytes as before. ; ; ; ; To use these routines begin with unsigned value to be divided (0-255) in the accumulator, ; and the routine will finish with the integer result in the accumulator. ; ; - All divisions (2-32) are covered below ; - X, Y, and BCD mode are not used by any of these routines ; - All these routines are constant cycles ; - Most routines require 1 temp register ;Divide by 2 (trival) ;1 byte, 2 cycles lsr ;Divide by 3 ;18 bytes, 30 cycles sta temp lsr adc #21 lsr adc temp ror lsr adc temp ror lsr adc temp ror lsr ;Divide by 4 (trival) ;2 bytes, 4 cycles lsr lsr ;Divide by 5 ;18 bytes, 30 cycles sta temp lsr adc #13 adc temp ror lsr lsr adc temp ror adc temp ror lsr lsr ;Divide by 6 ;17 bytes, 30 cycles lsr sta temp lsr lsr adc temp ror lsr adc temp ror lsr adc temp ror lsr ;Divide by 7 (From December '84 Apple Assembly Line) ;15 bytes, 27 cycles sta temp lsr lsr lsr adc temp ror lsr lsr adc temp ror lsr lsr ;Divide by 8 (trival) ;3 bytes, 6 cycles lsr lsr lsr ;Divide by 9 ;17 bytes, 30 cycles sta temp lsr lsr lsr adc temp ror adc temp ror adc temp ror lsr lsr lsr ;Divide by 10 ;17 bytes, 30 cycles lsr sta temp lsr adc temp ror lsr lsr adc temp ror adc temp ror lsr lsr ;Divide by 11 ;20 bytes, 35 cycles sta temp lsr lsr adc temp ror adc temp ror adc temp ror lsr adc temp ror lsr lsr lsr ;Divide by 12 ;17 bytes, 30 cycles lsr lsr sta temp lsr adc temp ror lsr adc temp ror lsr adc temp ror lsr ; Divide by 13 ; 21 bytes, 37 cycles sta temp lsr adc temp ror adc temp ror adc temp ror lsr lsr clc adc temp ror lsr lsr lsr ;Divide by 14 ;1/14 = 1/7 * 1/2 ;16 bytes, 29 cycles sta temp lsr lsr lsr adc temp ror lsr lsr adc temp ror lsr lsr lsr ;Divide by 15 ;14 bytes, 24 cycles sta temp lsr adc #4 lsr lsr lsr adc temp ror lsr lsr lsr ;Divide by 16 (trival) ;4 bytes, 8 cycles lsr lsr lsr lsr ;Divide by 17 ;18 bytes, 30 cycles sta temp lsr adc temp ror adc temp ror adc temp ror adc #0 lsr lsr lsr lsr ;Divide by 18 = 1/9 * 1/2 ;18 bytes, 32 cycles sta temp lsr lsr lsr adc temp ror adc temp ror adc temp ror lsr lsr lsr lsr ;Divide by 19 ;17 bytes, 30 cycles sta temp lsr adc temp ror lsr adc temp ror adc temp ror lsr lsr lsr lsr ;Divide by 20 ;18 bytes, 32 cycles lsr lsr sta temp lsr adc temp ror lsr lsr adc temp ror adc temp ror lsr lsr ;Divide by 21 ;20 bytes, 36 cycles sta temp lsr adc temp ror lsr lsr lsr lsr adc temp ror adc temp ror lsr lsr lsr lsr ;Divide by 22 ;21 bytes, 34 cycles lsr cmp #33 adc #0 sta temp lsr adc temp ror adc temp ror lsr adc temp ror lsr lsr lsr ;Divide by 23 ;19 bytes, 34 cycles sta temp lsr lsr lsr adc temp ror adc temp ror lsr adc temp ror lsr lsr lsr lsr ;Divide by 24 ;15 bytes, 27 cycles lsr lsr lsr sta temp lsr lsr adc temp ror lsr adc temp ror lsr ;Divide by 25 ;16 bytes, 29 cycles sta temp lsr lsr lsr adc temp ror lsr adc temp ror lsr lsr lsr lsr ;Divide by 26 ;21 bytes, 37 cycles lsr sta temp lsr adc temp ror adc temp ror adc temp ror lsr lsr adc temp ror lsr lsr lsr ;Divide by 27 ;15 bytes, 27 cycles sta temp lsr adc temp ror lsr lsr adc temp ror lsr lsr lsr lsr ;Divide by 28 ;14 bytes, 24 cycles lsr lsr sta temp lsr adc #2 lsr lsr adc temp ror lsr lsr ;Divide by 29 ;20 bytes, 36 cycles sta temp lsr lsr adc temp ror adc temp ror lsr lsr lsr adc temp ror lsr lsr lsr lsr ;Divide by 30 ;14 bytes, 26 cycles sta temp lsr lsr lsr lsr sec adc temp ror lsr lsr lsr lsr ;Divide by 31 ;14 bytes, 26 cycles sta temp lsr lsr lsr lsr lsr adc temp ror lsr lsr lsr lsr ;Divide by 32 (trival) ;5 bytes, 10 cycles lsr lsr lsr lsr lsr

ref https://atariage.com/forums/blogs/entry/10805-unsigned-integer-division-routines/

base/8bit_divide_by_constant_8bit_result.txt · Last modified: 2020-04-09 21:31 by ftc