时间差 php从两个指定的时间输出时多长时间以前的格式

/**
* Formats a timestamp nicely with an adaptive "x units of time ago" message.
* Only handles past dates.
* @return string Nicely-formatted message for the timestamp.
* @param $time Output of strtotime() on your choice of timestamp.
*/
function ago($time) {
  $time = strtotime($time);
  $delta = time() - $time;
  if ($delta < 60) {
    return 'less than a minute ago.';
  } else if ($delta < 120) {
    return 'about a minute ago.';
  } else if ($delta < (45 * 60)) {
    return floor($delta / 60) . ' minutes ago.';
  } else if ($delta < (90 * 60)) {
    return 'about an hour ago.';
  } else if ($delta < (24 * 60 * 60)) {
    return 'about ' . floor($delta / 3600) . ' hour(s) ago.';
  } else if ($delta < (48 * 60 * 60)) {
    return '1 day ago.';
  } else {
    return floor($delta / 86400) . ' days ago.';
  }
}