void putInt(ByteBuffer buf, int adr, int x) {
        buf.elems[adr  ] = (byte)((x >> 24) & 0xFF);
        buf.elems[adr+1] = (byte)((x >> 16) & 0xFF);
        buf.elems[adr+2] = (byte)((x >>  8) & 0xFF);
        buf.elems[adr+3] = (byte)((x      ) & 0xFF);
    }