switching.s

    .setcpu     "6502"
    .smart      on
    .autoimport on
    .importzp   sp, sreg, regsave, regbank
    .importzp   tmp1, tmp2, tmp3, tmp4, ptr1, ptr2, ptr3, ptr4
    .export     _turn_on, _turn_off, _toggle, _turn_up, _turn_double_up
    .export     _turn_down
    .import     _row

.macro loop_start
    sta tmp1    ; tmp1 = j
    stx tmp1+1

    ldy #0      ; ptr1 = tmp3 = i
    lda (sp),y
    sta tmp3
    sta ptr1
    iny
    lda (sp),y
    sta tmp3+1
    sta ptr1+1

    lda ptr1    ; ptr1 = ptr1 * 2 + _row (= &row[i])
    asl
    rol ptr1+1
    clc
    adc #<_row
    sta ptr1
    lda ptr1+1
    adc #>_row
    sta ptr1+1

    sec     ; tmp1 = tmp1 - tmp3 (= j - i)
    lda tmp1
    sbc tmp3
    sta tmp1
    lda tmp1+1
    sbc tmp3+1
    sta tmp1+1
.endmacro

.macro loop_end
    .local exit_loop

    lda tmp1    ; tmp1 == 0?
    ora tmp1+1
    beq exit_loop
    dec tmp1    ; tmp1 -= 1
    lda tmp1
    cmp #$ff
    bne loop
    dec tmp1+1
    jmp loop
exit_loop:
    jmp incsp2
.endmacro


.code

_turn_on:
    ldy #1
    .byte $2c   ; BIT $????
_turn_off:
    ldy #0

.proc turn_common
    sty selfmod+1

    loop_start

    ldy #0
loop:
selfmod:
    lda #$ff
    sta (ptr1),y
    iny
    iny
    bne skip1
    inc ptr1+1
skip1:
    loop_end
.endproc

.proc _toggle
    loop_start

    ldy #0
loop:
    lda (ptr1),y
    eor #1
    sta (ptr1),y
    iny
    iny
    bne skip1
    inc ptr1+1
skip1:
    loop_end
.endproc

_turn_up:
    ldy #1
    .byte $2c   ; BIT $????
_turn_double_up:
    ldy #2

.proc turn_up_common
    sty selfmod+1
    loop_start

    ldy #0
loop:
    clc
    lda (ptr1),y
selfmod:
    adc #$ff
    sta (ptr1),y
    iny
    lda (ptr1),y
    adc #0
    sta (ptr1),y
    iny
    bne skip1
    inc ptr1+1
skip1:
    loop_end
.endproc

.proc _turn_down
    loop_start

    ldy #0
loop:
    lda (ptr1),y
    iny
    ora (ptr1),y
    beq skip0

    dey
    sec
    lda (ptr1),y
    sbc #1
    sta (ptr1),y
    iny
    lda (ptr1),y
    sbc #0
    sta (ptr1),y
skip0:
    iny
    bne skip1
    inc ptr1+1
skip1:
    loop_end
.endproc