计算php代码执行时间长短的类(精确到毫秒)

<?php
/**
 * PHP脚本执行时间计算
 */
class runtime
{
    var $StartTime = 0;
    var $StopTime = 0;




    function get_microtime()
    {
        list($usec, $sec) = explode(" ", microtime());
//var_dump($usec);var_dump($sec);
        return ((float)$usec + (float)$sec);
    }




    function start()
    {
        $this->StartTime = $this->get_microtime();
    }




    function stop()
    {
        $this->StopTime = $this->get_microtime();
    }




    function spent($echo=false,$title="")
    {
//秒
        $spent = sprintf("%.4f",round(($this->StopTime - $this->StartTime) * 1000, 1));
        //毫秒
//$msec = $spent*1000;
        if($echo){
            echo  $title."执行时间:{$spent}毫秒<br/>";
        }else{
            return $spent;
        }
    }
    function clear()
    {
        $this->StartTime = 0;
        $this->StopTime = 0;
    }




}




#测试脚本代码
$runtime= new runtime;
$runtime->start();
$a = 0;
for($i=0; $i<100000; $i++)
{
    $a *= $i;
}
$runtime->stop();




$spent_time = $runtime->spent($echo=true, "测试脚本");
$runtime->clear();


?>