System.Globalization.EastAsianLunisolarCalendar.IsLeapDay C# (CSharp) Method

        public override bool IsLeapDay(int year, int month, int day, int era) {
            year = CheckYearMonthRange(year, month, era);
            int daysInMonth = InternalGetDaysInMonth(year, month);

            if (day < 1 || day > daysInMonth) {
                throw new ArgumentOutOfRangeException(
                            "day",
                            String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("ArgumentOutOfRange_Day"), daysInMonth, month));
            }
            int m = GetYearInfo(year, LeapMonth);
            return ((m!=0) && (month == (m+1)));
        }