PHP计算时间差，并返回什么时间之前发表的内容

<?php
header("Content-type: text/html; charset=utf-8"); 
function time2Units ($time){
　　$year = floor($time / 60 / 60 / 24 / 365);
　　$time -= $year * 60 * 60 * 24 * 365;
　　$month = floor($time / 60 / 60 / 24 / 30);
　　$time -= $month * 60 * 60 * 24 * 30;
　　$week = floor($time / 60 / 60 / 24 / 7);
　　$time -= $week * 60 * 60 * 24 * 7;
　　$day = floor($time / 60 / 60 / 24);
　　$time -= $day * 60 * 60 * 24;
　　$hour = floor($time / 60 / 60);
　　$time -= $hour * 60 * 60;
　　$minute = floor($time / 60);
　　$time -= $minute * 60;
　　$second = $time;
　　$elapse = '';
　　$unitArr = array('年' =>'year', '个月'=>'month', '周'=>'week', '天'=>'day',
　　　　'小时'=>'hour', '分钟'=>'minute', '秒'=>'second'
　　);
　　foreach ( $unitArr as $cn => $u ){
　　　　if ( $$u > 0 ){
　　　　　　$elapse = $$u . $cn;
　　　　　　break;
　　　　}
　　}
　　return $elapse;
}
$past = strtotime("2015-01-12 21:49:00"); // Some timestamp in the past
$now = time(); // Current timestamp
$diff = $now - $past;
echo '发表于' . time2Units($diff) . '前';

?>