internal override LocalInstant AddMonths(LocalInstant localInstant, int months)
{
// Note: this method gives the same result regardless of the month numbering used
// by the instance. The method works in terms of civil month numbers for most of
// the time in order to simplify the logic.
if (months == 0)
{
return(localInstant);
}
long tickOfDay = TimeOfDayCalculator.GetTickOfDay(localInstant);
var startDate = HebrewScripturalCalculator.HebrewFromAbsolute(AbsoluteDayFromLocalInstant(localInstant));
int year = startDate.Year;
int month = HebrewMonthConverter.ScripturalToCivil(year, startDate.Month);
// This arithmetic works the same both backwards and forwards.
year += (months / MonthsPerLeapCycle) * YearsPerLeapCycle;
months = months % MonthsPerLeapCycle;
if (months > 0)
{
// Add as many months as we need to in order to act as if we'd begun at the start
// of the year, for simplicity.
months += month - 1;
// Add a year at a time
while (months >= GetMaxMonth(year))
{
months -= GetMaxMonth(year);
year++;
}
// However many months we've got left to add tells us the final month.
month = months + 1;
}
else
{
// Pretend we were given the month at the end of the years.
months -= GetMaxMonth(year) - month;
// Subtract a year at a time
while (months + GetMaxMonth(year) <= 0)
{
months += GetMaxMonth(year);
year--;
}
// However many months we've got left to add (which will still be negative...)
// tells us the final month.
month = GetMaxMonth(year) + months;
}
// Convert back to scriptural for the last bit
month = HebrewMonthConverter.CivilToScriptural(year, month);
int day = Math.Min(HebrewScripturalCalculator.DaysInMonth(year, month), startDate.Day);
int absoluteDay = HebrewScripturalCalculator.AbsoluteFromHebrew(year, month, day);
return(LocalInstantFromAbsoluteDay(absoluteDay, tickOfDay));
}
private int CivilToCalendarMonth(int year, int month) => monthNumbering == HebrewMonthNumbering.Civil ? month : HebrewMonthConverter.CivilToScriptural(year, month);