php计算页面执行时间代码

<? 

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  "<hr>"; 
        $timer->stop(); 

        echo  $timer->elapsed(); 

*/ 
?>