protected function _computeKey($key)
    {
        $spaces = 0;
        $digits = '';

        for ($i = 0, $s = mb_orig_strlen($key); $i < $s; ++$i) {
            $c = mb_orig_substr($key, $i, 1);

            if ($c === "\x20") {
                ++$spaces;
            } elseif (ctype_digit($c)) {
                $digits .= $c;
            }
        }

        if ($spaces > 0) {
            $result = (float)floor($digits / $spaces);
        } else {
            $result = (float)$digits;
        }

        return pack('N', $result);
    }