static int readTagNumber(InputStream s, int tag)
            throws IOException
    {
        int tagNo = tag & 0x1f;

        //
        // with tagged object tag number is bottom 5 bits, or stored at the start of the content
        //
        if (tagNo == 0x1f)
        {
            int b = s.read();
            if (b < 31)
            {
                if (b < 0)
                {