PHP 计算程序运行时间

<?php
class Timer {
	var $StartTime = 0;
	var $StopTime = 0;
	var $TimeSpent = 0;
	function start(){
		$this->StartTime = microtime();
	}
	function stop(){
		$this->StopTime = microtime();
	}
	function spent() {
		if ($this->TimeSpent) {
			return $this->TimeSpent;
		} else {
			$StartMicro = substr($this->StartTime,0,10);
			$StartSecond = substr($this->StartTime,11,10);
			$StopMicro = substr($this->StopTime,0,10);
			$StopSecond = substr($this->StopTime,11,10);
			$start = doubleval($StartMicro) + $StartSecond;
			$stop = doubleval($StopMicro) + $StopSecond;
			$this->TimeSpent = $stop - $start;
			return substr($this->TimeSpent,0,8)."秒";
		}
	}
}

$timer = new Timer();
$timer->start();
$temp=0;
for($i=0;$i<1000;$i++) for($j=0;$j<$i;$j++) $temp ++;
$timer->stop();
echo "循环 $temp 次，运行时间为 ".$timer->spent();
 ?>