qq空间的g_tk算法

function token(){
    $path = 'cookie.txt';//cookie文件
    if(file_exists($path)){
        $fp=fopen($path,"r");
        while(!(feof($fp)))
        {
         $text=fgets($fp);
            if(preg_match("/(;)skey=(.*)(;)RK=/", $text, $matches)){
                $str = trim($matches[2]);
                break;
            }
        }
    }else{
        echo 'cookie文件不存在';
        die();
    }
    $hash = 5381;
    for($i=0,$l=mb_strlen($str,'utf-8');$i<$l;++$i){        
            $hash = $hash + uniord(mb_substr($str,$i,1,'utf-8'))+($hash<<5);
            
    }
    $g_tk = $hash&0x7fffffff;
    return $g_tk;
}