loop:
    lda (src),y
    asl
    rol temp
    asl
    rol temp
    ora (dest,x)
    sta (dest,x)
    inc dest
    lda temp
    and #3
    ora (dest,x)
    sta (dest,x)
    clc
    lda dest
    adc #rowSpacing
    sta dest
    dey
    bmi done
    bcc loop
    inc dest+1
    bcs loop
  done:

loop:
    lda (src),y
    sta (dest,x)
    dey
    bmi done
    lda dest
    adc #rowSpacing
    sta dest
    bcc loop
    inc dest+1
    bcs loop