当天距离过去的第几天算法

php代码如下

  private function getDateArr()
   {
        $days = array_merge(range(1, 50), [60, 70, 80, 90, 120, 150, 180, 210, 240, 300, 330, 360]);
        foreach ($days as $day) {
            $dateArr[$day] = date('Y-m-d', strtotime("-{$day} day", time()));
        }
        $this->dateArrFlip = array_flip($dateArr);
   }