omult12.a

; omult12.a
; from 'Gateway to Apshai' for the Atari 8-bit family, http://bringerp.free.fr/RE/Gta/downloads.php5
; optimised to remove use of 'result'
;
; 8 bit x 8 bit unsigned multiply, 8 bit result (low byte)
; Average cycles: 181.04
; 27 bytes

localA = $02
localX = $03
result = $04

* = $0200

mulAbyX
    stx localX
    cmp localX
    bcc +
    sta localX
    txa

+
    sta localA
    lda #0
;    sta result

-
    lsr localA
    php
    bcc +
;    lda result
    clc
    adc localX
;    sta result

+
    asl localX
    plp
    bne -
 ;   lda result
    rts