/// <summary>
/// Adds the specified number of days to the value of this instance.
/// </summary>
/// <param name="numberOfDays">A number of whole days.
/// The value parameter can be negative or positive.</param>
public CivilDate AddDays(long numberOfDays)
{
RataDie currentValue = null;
currentValue = ToRataDie();
currentValue.Days += numberOfDays;
return(CivilDate.FromRataDie(currentValue));
}
/// <summary>
/// Returns a <see cref="CivilDate"/> object set to a date based on its <see cref="RataDie"/> counterpart.
/// <remarks>See the footnote on page 384 of "Calendrical Calculations, Part II: Three Historical Calendars"
/// by E. M. Reingold, N. Dershowitz, and S. M. Clamen, Software--Practice and Experience, Volume 23,
/// Number 4 (April, 1993), pages 383-404 for an explanation.</remarks>
/// </summary>
/// <param name="fixedDate">An <see cref="RataDie"/> object that represents the desired date.</param>
public static CivilDate FromRataDie(RataDie fixedDate)
{
int day = 0;
int year = 0;
int month = 0;
int mlen = 0;
long d0 = 0L;
long n400 = 0L;
long d1 = 0L;
long n100 = 0L;
long d2 = 0L;
long n4 = 0L;
long d3 = 0L;
long n1 = 0L;
CivilDate result = null;
d0 = fixedDate.Days - 1L;
n400 = (int)(d0 / 146097L);
d1 = (int)(d0 % 146097L);
n100 = (int)(d1 / 36524L);
d2 = (int)(d1 % 36524L);
n4 = (int)(d2 / 1461L);
d3 = (int)(d2 % 1461L);
n1 = (int)(d3 / 365L);
day = (int)((d3 % 365L) + 1L);
year = (int)(400L * n400 + 100L * n100 + 4L * n4 + n1);
if (n100 == 4L || n1 == 4L)
{
result = new CivilDate(year, CivilMonth.December, 31);
}
else
{
year++;
month = 1; // Start from January
while ((mlen = GetDaysInMonth(year, (CivilMonth)month)) < day)
{
day -= mlen;
month++;
}
result = new CivilDate(year, (CivilMonth)month, day);
}
return(result);
}
/// <summary>
/// Converts the date to the number of days elapsed between the Gregorian date 12/31/1 BC and the date.
/// The Gregorian date Sunday, December 31, 1 BC is imaginary.
/// </summary>
/// <returns>The number of days elapsed since 12/31/1 BC.</returns>
public RataDie ToRataDie()
{
long julianLeapYears = 0;
long centuryYears = 0;
long gregorianLeapYears = 0;
RataDie result = null;
result = new RataDie();
julianLeapYears = (int)((Year - 1) / 4);
centuryYears = (int)((Year - 1) / 100);
gregorianLeapYears = (int)((Year - 1) / 400);
result.Days = ((long)DayOfYear /* days this year */
+ 365L * (long)(Year - 1) /* + days in prior years */
+ (long)(julianLeapYears /* + Julian Leap years */
- centuryYears /* - century years */
+ gregorianLeapYears)); /* + Gregorian leap years */
return(result);
}