prompt rb 8 ; prompt string here, null terminated

    str2lng:

        push ax bx

        xor ax,ax
        xor bx,bx
        xor cx,cx

        mov si,prompt
        mov al,[si]

    @@:

        sub al,'0'
        add cx,ax

        inc si

        mov al,[si]

        cmp al,0
        je @f

        shl cx,1
        mov bx,cx
        shl cx,2
        add cx,bx
        jmp @b

    @@:

        pop bx ax
        ret