System.Globalization.Calendar.AddDays C# (CSharp) Method

        public virtual DateTime AddDays(DateTime time, int days) {
            return (Add(time, days, MillisPerDay));
        }

      /// <summary>
      /// Determines if the specified <paramref name="year"/> is a valid year value.
      /// </summary>
      /// <param name="year">The year value.</param>
      /// <param name="cal">The calendar to use.</param>
      /// <param name="era">The era the year belongs to.</param>
      /// <returns>true if it's a valid year value; false otherwise.</returns>
      private static bool IsValidYear(int year, Calendar cal, int era)
      {
         int minYear = cal.GetYear(cal.MinSupportedDateTime.Date);
         int maxYear = cal.GetYear(cal.MaxSupportedDateTime.Date);

         if (cal.Eras.Length > 1)
         {
            DateTime? minDate = null, maxDate = null;

            DateTime date = cal.MinSupportedDateTime;

            while (date < cal.MaxSupportedDateTime.Date)
            {
               int e = cal.GetEra(date);

               if (e == era)
               {
                  if (minDate == null)
                  {
                     minDate = date;
                  }

                  maxDate = date;
               }

               date = cal.AddDays(date, 1);
            }

            minYear = cal.GetYear(minDate.GetValueOrDefault(cal.MinSupportedDateTime.Date));
            maxYear = cal.GetYear(maxDate.GetValueOrDefault(cal.MaxSupportedDateTime.Date));
         }

         year = cal.ToFourDigitYear(year);

         return year >= minYear && year <= maxYear;
      }