// ------------------------------------------------------------------
// Fields to time
// ------------------------------------------------------------------
/// <summary>
/// Return the Chinese new year of the given Gregorian year.
/// </summary>
///
/// <param name="gyear">a Gregorian year</param>
/// <returns>days after January 1, 1970 0:00 Asia/Shanghai of the Chinese new
/// year of the given year (this will be a new moon)</returns>
private int NewYear(int gyear)
{
long cacheValue = newYearCache.Get(gyear);
if (cacheValue == IBM.ICU.Impl.CalendarCache.EMPTY)
{
int solsticeBefore = WinterSolstice(gyear - 1);
int solsticeAfter = WinterSolstice(gyear);
int newMoon1 = NewMoonNear(solsticeBefore + 1, true);
int newMoon2 = NewMoonNear(newMoon1 + SYNODIC_GAP, true);
int newMoon11 = NewMoonNear(solsticeAfter + 1, false);
if (SynodicMonthsBetween(newMoon1, newMoon11) == 12 &&
(HasNoMajorSolarTerm(newMoon1) || HasNoMajorSolarTerm(newMoon2)))
{
cacheValue = NewMoonNear(newMoon2 + SYNODIC_GAP, true);
}
else
{
cacheValue = newMoon2;
}
newYearCache.Put(gyear, cacheValue);
}
return((int)cacheValue);
}
/// <summary>
/// Finds the day # of the first day in the given Hebrew year. To do this, we
/// want to calculate the time of the Tishri 1 new moon in that year.
/// <p>
/// The algorithm here is similar to ones described in a number of
/// references, including:
/// <ul>
/// <li>"Calendrical Calculations", by Nachum Dershowitz & Edward Reingold,
/// Cambridge University Press, 1997, pages 85-91.
/// <li>Hebrew Calendar Science and Myths, <a
/// href="http://www.geocities.com/Athens/1584/">
/// http://www.geocities.com/Athens/1584/</a>
/// <li>The Calendar FAQ, <a href="http://www.faqs.org/faqs/calendars/faq/">
/// http://www.faqs.org/faqs/calendars/faq/</a>
/// </ul>
/// </summary>
///
private static long StartOfYear(int year)
{
long day = cache.Get(year);
if (day == IBM.ICU.Impl.CalendarCache.EMPTY)
{
int months = (235 * year - 234) / 19; // # of months before year
long frac = months * MONTH_FRACT + BAHARAD; // Fractional part of
// day #
day = months * 29 + (frac / DAY_PARTS); // Whole # part of
// calculation
frac = frac % DAY_PARTS; // Time of day
int wd = (int)(day % 7); // Day of week (0 == Monday)
if (wd == 2 || wd == 4 || wd == 6)
{
// If the 1st is on Sun, Wed, or Fri, postpone to the next day
day += 1;
wd = (int)(day % 7);
}
if (wd == 1 && frac > 15 * HOUR_PARTS + 204 && !IsLeapYear(year))
{
// If the new moon falls after 3:11:20am (15h204p from the
// previous noon)
// on a Tuesday and it is not a leap year, postpone by 2 days.
// This prevents 356-day years.
day += 2;
}
else if (wd == 0 && frac > 21 * HOUR_PARTS + 589 &&
IsLeapYear(year - 1))
{
// If the new moon falls after 9:32:43 1/3am (21h589p from
// yesterday noon)
// on a Monday and *last* year was a leap year, postpone by 1
// day.
// Prevents 382-day years.
day += 1;
}
cache.Put(year, day);
}
return(day);
}
// ------------------------------------------------------------------
// Astronomical computations
// ------------------------------------------------------------------
/// <summary>
/// Return the major solar term on or after December 15 of the given
/// Gregorian year, that is, the winter solstice of the given year.
/// Computations are relative to Asia/Shanghai time zone.
/// </summary>
///
/// <param name="gyear">a Gregorian year</param>
/// <returns>days after January 1, 1970 0:00 Asia/Shanghai of the winter
/// solstice of the given year</returns>
private int WinterSolstice(int gyear)
{
long cacheValue = winterSolsticeCache.Get(gyear);
if (cacheValue == IBM.ICU.Impl.CalendarCache.EMPTY)
{
// In books December 15 is used, but it fails for some years
// using our algorithms, e.g.: 1298 1391 1492 1553 1560. That
// is, winterSolstice(1298) starts search at Dec 14 08:00:00
// PST 1298 with a final result of Dec 14 10:31:59 PST 1299.
long ms = DaysToMillis(ComputeGregorianMonthStart(gyear, IBM.ICU.Util.Calendar.DECEMBER)
+ 1 - IBM.ICU.Util.Calendar.EPOCH_JULIAN_DAY);
astro.SetTime(ms);
// Winter solstice is 270 degrees solar longitude aka Dongzhi
long solarLong = astro.GetSunTime(
IBM.ICU.Impl.CalendarAstronomer.WINTER_SOLSTICE, true);
cacheValue = MillisToDays(solarLong);
winterSolsticeCache.Put(gyear, cacheValue);
}
return((int)cacheValue);
}