System.Globalization.GregorianCalendar.GetAbsoluteDate C# (CSharp) Méthode

        internal static long GetAbsoluteDate(int year, int month, int day) {
            if (year >= 1 && year <= MaxYear && month >= 1 && month <= 12)
            {
                int[] days = ((year % 4 == 0 && (year % 100 != 0 || year % 400 == 0))) ? DaysToMonth366: DaysToMonth365;
                if (day >= 1 && (day <= days[month] - days[month - 1])) {
                    int y = year - 1;
                    int absoluteDate = y * 365 + y / 4 - y / 100 + y / 400 + days[month - 1] + day - 1;
                    return (absoluteDate);
                }
            }
            throw new ArgumentOutOfRangeException(null, Environment.GetResourceString("ArgumentOutOfRange_BadYearMonthDay"));
        }

        /*=================================GetAbsoluteDateUmAlQura==========================
        **Action: Gets the Absolute date for the given UmAlQura date.  The absolute date means
        **       the number of days from January 1st, 1 A.D.
        **Returns:
        **Arguments:
        **Exceptions:
        ============================================================================*/
        private static long GetAbsoluteDateUmAlQura(int year, int month, int day)
        {
            //Caller should check the validaty of year, month and day.

            int yg = 0, mg = 0, dg = 0;
            ConvertHijriToGregorian(year, month, day, ref yg, ref mg, ref dg);
            return GregorianCalendar.GetAbsoluteDate(yg, mg, dg);
        }