Calculate the time difference between two timestamps

//Function: Calculate the day, hour, minute and second difference between two timestamps
//$begin_time start timestamp
//$end_time end timestamp
function timediff($begin_time,$end_time)
{
      if($begin_time < $end_time){
         $starttime = $begin_time;
         $endtime = $end_time;
      }else{
         $starttime = $end_time;
         $endtime = $begin_time;
      }

      //calculate the number of days
      $timediff = $endtime-$starttime;
      $days = intval($timediff/86400);
      //calculate hours
      $remain = $timediff%86400;
      $hours = intval($remain/3600);
      //calculate minutes
      $remain = $remain%3600;
      $mins = intval($remain/60);
      // count seconds
      $secs = $remain%60;
      $res = array("day" => $days,"hour" => $hours,"min" => $mins,"sec" => $secs);
      return $res;
}

print_r(timediff(strtotime(2016-09-12 12:00:00'),strtotime('2016-09-15 21:50:21')));