div_mul16.asm

[bogax]

edit: Multiply is buggy! I forgot to propagate the carry

 

 

 

Here is a replacement for the 8 * 8 = 16 multiplication
and 8 / 8 division with remainder routines.

I haven't tested them exhaustively yet but they seem to work

  ; enter with multipcands in a, y
  ; a * b result hi in temp2, lo in a
  ; by bogax
 
mul16
  dey
  sty temp1
  sta temp2
  ldx #$07
  lda #$00
mul_loop
  asl
  rol temp2
  bcc mul_no_add
  adc temp1
mul_no_add
  dex
  bpl mul_loop
  rts

  ; a / y 
  ; returns quotient in a, remainder in y and temp1, divisor in temp2
  ; by bogax

div16
  sty temp2 ; divisor
  asl ; dividend
  sta temp1 ; quotient/dividend
  lda #$00
  ldx #$07
div_loop
  rol ; remainder
  cmp temp2 ; divisor
  bcc div_next
  sbc temp2 ; divisor
div_next
  rol temp1 ; quotient/dividend
  dex
  bpl div_loop
  tay
  lda temp1
  sty temp1
  rts

Edited August 31, 2014 by bogax