128-bit numbers addition

    lea Number_A,a0
    lea Number_B,a1
    movem.l (a0),d0-d3      ; unpack 128-bit number
    add.l   (a1)+,d0
    addx.l  (a1)+,d1
    addx.l  (a1)+,d2
    addx.l  (a1)+,d3
    movem.l d0-d3,(a0)      ; pack 128-bit number