How to calculate string similarity using similar_text method in php

<?php 
/*
 *
 * @param string $title_1 题目1
 * @param string $title_2 题目2
 * @return float $percent 相似百分比
 */
function title_similar($title_1,$title_2) {
  $title_1 = get_real_title($title_1);
  $title_2 = get_real_title($title_2);
  similar_text($title_1, $title_2, $percent);
  return $percent;
}
/**
 * php采集文章题目并去版权
 * @param string $html 需要采集的html源代码
 * @return string
 */
function get_real_title($str){
  $str = str_replace(array(&#39;-&#39;,&#39;—&#39;,&#39;|&#39;),&#39;_&#39;,$str);
  $splits = explode(&#39;_&#39;, $str);
  $l = 0;
  foreach ($splits as $tp){
    $len = strlen($tp);
    if ($l < $len){$l = $len;$tt = $tp;}
  }
  $tt = trim(htmlspecialchars($tt));
  return $tt;
}
//以下是测试
$title_1 = &#39;代号PHPCMS V9产品正式发布公测版本&#39;;
$title_2 = &#39;PHPCMS再战江湖 V9产品正式发布公测版本&#39;;
$percent = title_similar($title_1,$title_2);
echo &#39;相似百分比：&#39;.$percent.&#39;%&#39;;
echo "<br />\n";
?>