multiply_test/tests/mult77.a at main · TobyLobster/multiply_test · GitHub

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; mult77.a
; from 'Instrumentation of a Savonius wind turbine' by Samuel Martin Babb (1979) https://archive.org/details/instrumentationo00babb/page/108/mode/2up
;
; 8 bit x 8 bit unsigned multiply, 16 bit result
; Average cycles: 288.00
; 43 bytes

mul1    = $02   ; multiplier
mul1h   = $03   ; temp
mul2    = $04   ; multiplicand
lowmp   = $05   ; product (low)
highmp  = $06   ; product (high)

* = $0200

mult
    lda #0
    sta highmp
    sta lowmp
    sta mul1h
    tax
    lsr mul2
    bcs run
itiso
    cpx #7
    beq don
    inx
    asl mul1
    rol mul1h
    lsr mul2
    bcc itiso
run
    lda mul1
    clc
    adc lowmp
    sta lowmp
    lda mul1h
    adc highmp
    sta highmp
    jmp itiso
don
    rts