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

        internal static long GetAbsoluteDate(int year, int month, int day) {
            if (year >= 1 && year <= 9999 && 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"));
        }        

 internal static long DateToTicks(int year, int month, int day)
 {
     return(GregorianCalendarHelper.GetAbsoluteDate(year, month, day) * 864000000000L);
 }