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base: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: 2020-02-09 12:30 by djmips