对于非常基本的标记，这些正则表达式是否有效?

只是一个关于正则表达式的快速问题:这段代码是否适用于我需要做的任何修饰?(也就是说，这是否可以安全地输入数据库?)

function markdown2html($text) {
        $text = htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
    // Strong Emphasis
    $text = preg_replace('/__(.+?)__/s', '<strong>$1</strong>', $text);
    $text = preg_replace('/'*'*(.+?)'*'*/s', '<strong>$1</strong>', $text);
    // Underline
    $text = preg_replace('/_([^_]+)_/', '<p style="text-decoration: underline;">$1</p>', $text);
    //Italic
    $text = preg_replace('/'*([^'*]+)'*/', '<em>$1</em>', $text);
    // Windows to Unix
    $text = str_replace(''r'n', ''n', $text);
    // Macintosh to Unix
    $text = str_replace(''r', ''n', $text);
    //Paragraphs
    $text = '<p>' . str_replace("'n'n", '</p><p>', $text) . '</p>';
    $text = str_replace("'n", '<br />', $text);
    // [Linked Text](Url)   
   $text = preg_replace('/'[([^']]+)]'(([a-z0-9._~:'/?#@!$&''()*+,;=%]+)')/i', '<a href="$2">$1</a>', $text);
   return $text;
}