解析PHP计算页面执行时间的实现代码

<?php
 $t = new executetime;
 phpinfo();
 class executetime{
     private $microtime;
     public function __construct(){
         $this->microtime = microtime(true);
     }

         public function getnow(){
                 $this->__dectruct();
         }

     public function __destruct(){
         if (empty($_server['request_time_float']))
             echo '<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次执行时间：', microtime(true) - $this->microtime, '秒</div>';
         else
             echo '<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次执行时间：', microtime(true) - $_server['request_time_float'], '秒</div>';
     }
 }