нод

        model tiny
        stack 100h
.data
        aaaa db 15
        bbb db 20
.code
        org 100h
start:
        mov ax, @data
        mov ds, ax
        mov es, ax

        mov dl, aaaa
        mov bl, bbb
        mov dh, 0
        mov bh, 0

l:
        cmp bx, 0
        JLE end_dx
        cmp dx, 0
        JLE end_bx

        cmp bx, dx
        jb bx_less
        sub bx, dx
        jmp l

bx_less:
        sub dx, bx
        jmp l

end_bx:
        mov cx, ax
        jmp end_
end_dx:
        mov cx, dx

end_:
        mov ax, 4C00h
        int 21h

end start