php 计算代码执行时间

class runtime
{
var $StartTime = 0;
var $StopTime = 0;

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

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

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

function spent()
{
return round(($this->StopTime - $this->StartTime) * 1000, 1);
}

}

$run_time = new runtime();
$run_time->start();
//begin your code
//end your code
$run_time->stop();
echo "Script running time:".$run_time->spent()."ms";