if(!function_exists('cal_days_in_month')) {
    function cal_days_in_month($calendar, $month, $year) {
        return $month == 2 ? ($year % 4 ? 28 : ($year % 100 ? 29 : ($year % 400 ? 28 : 29))) : (($month - 1) % 7 % 2 ? 30 : 31);
    }

    if (!defined('CAL_GREGORIAN')) {
        define('CAL_GREGORIAN', 1);
    }
}