public function getContext()
    {
        $s = '';
        foreach (['a', 'b', 'c', 'd'] as $i) {
            $v = $this->{$i};
            $s .= chr($v & 0xff);
            $s .= chr(($v >> 8) & 0xff);
            $s .= chr(($v >> 16) & 0xff);
            $s .= chr(($v >> 24) & 0xff);
        }

        return $s;
    }