php截取中英文字串操作

<?php
class Zend_View_Helper_UserName
{
    public function userName($userName, $length)
    {
        $retUserName = &#39;&#39;;
        $position = 0;
        $count = 1;
        while ($count <= $length) {
            $subStr = mb_substr($userName, $position, 1, &#39;UTF-8&#39;);
            if (preg_match("/^[\x{4e00}-\x{9fa5}]+$/u", $subStr)) {
                $count += 2;
            } else {
                $count++;
            }
            $position++;
            $retUserName .= $subStr;
        }
        $retUserNameLength  = mb_strlen($retUserName);
        $userNameLength = mb_strlen($userName) ;
        if ($retUserNameLength >= $userNameLength - 1 && $retUserNameLength <= $userNameLength) {
            $retUserName = $userName;
        } else {
            $retUserName .= &#39;...&#39;;
        }
        return $retUserName;
    }
}