php返回相对时间（如：20分钟前，3天前）的方法，php天前

function plural($num) {
 if ($num != 1)
  return "s";
}
function getRelativeTime($date) {
 $diff = time() - strtotime($date);
 if ($diff<60)
  return $diff." 秒".plural($diff)." 前";
 $diff = round($diff/60);
 if ($diff<60)
  return $diff." 分钟".plural($diff)." 前";
 $diff = round($diff/60);
 if ($diff<24)
  return $diff." 小时".plural($diff)." 前";
 $diff = round($diff/24);
 if ($diff<7)
  return $diff." 天".plural($diff)." 前";
 $diff = round($diff/7);
 if ($diff<4)
  return $diff." 星期".plural($diff)." 前";
 return "on ".date("F j, Y", strtotime($date));
}