PHP判断一段时间内有几年，或几月，或几天

/**
     * @param $start 开始时间戳
     * @param $end 结束时间戳
     * @param string $type 判断相差几年或几月或几天，默认天
     */
    function date_numbers($start,$end,$type='d'){
        //转化日期格式为2018-8-28
        $start_m = date('Y-m-d',$start);
        $end_m = date('Y-m-d',$end);
        $date1 = explode('-',$start_m);
        $date2 = explode('-',$end_m);
        if ($type=='y'){
            //取绝对值，避免因年份大小产生的负值
            $number= abs($date1[0] - $date2[0]);
        }elseif ($type=='m'){
            //判断月份大小，进行相应加或减
            if($date1[1]<$date2[1]){
                $number= abs($date1[0] - $date2[0]) * 12 + abs($date1[1] - $date2[1]);
            }else{
                $number= abs($date1[0] - $date2[0]) * 12 - abs($date1[1] - $date2[1]);
            }
        }else{
            $time = $end-$start;
            $number = abs(intval($time/(3600*24)));
        }
        return $number;
    }