PHP calculation page execution time code

class  c_Timer  {
        var  $t_start  =  0;
        var  $t_stop  =  0;
        var  $t_elapsed  =  0;

        function  start()  {  $this->t_start  =  microtime();  }

        function  stop()    {  $this->t_stop    =  microtime();  }

        function  elapsed()  {
                if  ($this->t_elapsed)  {
                        return  $this->t_elapsed;
                }  else  {
                            $start_u  =  substr($this->t_start,0,10);
$start_s  =  substr($this->t_start,11,10);
                              $stop_u    =  substr($this->t_stop,0,10);
$stop_s    =  substr($this->t_stop,11,10);
                        $start_total  =  doubleval($start_u)  +  $start_s;
                              $stop_total    =  doubleval($stop_u)  +  $stop_s;

                        $this->t_elapsed  =  $stop_total  -  $start_total;

                        return  $this->t_elapsed;
                }
        }
};

/*  Here's  an  example  usage:

        $timer  =  new  c_Timer;

        $timer->start();
        echo  "";
        $timer->stop();

        echo  $timer->elapsed();

*/
?>

执行时间, php