PHP でスタック オーバーフローの自動リンク動作を模倣するにはどうすればよいですか?

<code class="php">function auto_link_text($text)
{
    // Daring Fireball's URL-matching regex pattern
    $pattern = '(?i)\b((?:[a-z][\w-]+:(?:/{1,3}|[a-z0-9%])|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}/)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:\'".,<>?«»“”‘’]))';

    // Regex callback function for URL processing
    $callback = create_function('$matches', '
        $url       = array_shift($matches);
        $url_parts = parse_url($url);

        $text = parse_url($url, PHP_URL_HOST) . parse_url($url, PHP_URL_PATH);
        $text = preg_replace("/^www./", "", $text);

        $last = -(strlen(strrchr($text, "/"))) + 1;
        if ($last < 0) {
            $text = substr($text, 0, $last) . "&amp;hellip;";
        }

        return sprintf(\'<a rel="nofollow" href="%s">%s</a>\', $url, $text);
    ');

    return preg_replace_callback($pattern, $callback, $text);
}</code>

<code class="php">$input_text = "This is my text.  I wonder if you know about asking questions on StackOverflow:
 Check This out http://www.stackoverflow.com/questions/1925455/how-to-mimic-stackoverflow-auto-link-behavior

 Also, base_convert php function?
http://pt.php.net/manual/en/function.base-convert.php#52450

http://pt.php.net/manual/en/function.base-convert.php?wtf=hehe#52450";

$output_text = auto_link_text($input_text);</code>

This is my text.  I wonder if you know about asking questions on StackOverflow:
Check This out http://www.stackoverflow.com/questions/1925455/how-to-mimic-stackoverflow-auto-link-behavior

Also, base_convert php function?
http://pt.php.net/manual/en/function.base-convert.php#52450

http://pt.php.net/manual/en/function.base-convert.php?wtf=hehe#52450

<code class="html">This is my text.  I wonder if you know about asking questions on StackOverflow:
Check This out <a rel="nofollow" href="http://www.stackoverflow.com/questions/1925455/how-to-mimic-stackoverflow-auto-link-behavior">stackoverflow.com/questions/1925455/&hellip;</a>

Also, base_convert php function?
<a rel="nofollow" href="http://pt.php.net/manual/en/function.base-convert.php#52450">pt.php.net/manual/en/&hellip;</a>

<a rel="nofollow" href="http://pt.php.net/manual/en/function.base-convert.php?wtf=hehe#52450">pt.php.net/manual/en/&hellip;</a></code>