internal virtual int GetDatePart(long ticks, int part)
{
// n = number of days since 1/1/0001
int n = (int)(ticks / TicksPerDay);
// y400 = number of whole 400-year periods since 1/1/0001
int y400 = n / DaysPer400Years;
// n = day number within 400-year period
n -= y400 * DaysPer400Years;
// y100 = number of whole 100-year periods within 400-year period
int y100 = n / DaysPer100Years;
// Last 100-year period has an extra day, so decrement result if 4
if (y100 == 4) y100 = 3;
// n = day number within 100-year period
n -= y100 * DaysPer100Years;
// y4 = number of whole 4-year periods within 100-year period
int y4 = n / DaysPer4Years;
// n = day number within 4-year period
n -= y4 * DaysPer4Years;
// y1 = number of whole years within 4-year period
int y1 = n / DaysPerYear;
// Last year has an extra day, so decrement result if 4
if (y1 == 4) y1 = 3;
// If year was requested, compute and return it
if (part == DatePartYear)
{
return (y400 * 400 + y100 * 100 + y4 * 4 + y1 + 1);
}
// n = day number within year
n -= y1 * DaysPerYear;
// If day-of-year was requested, return it
if (part == DatePartDayOfYear)
{
return (n + 1);
}
// Leap year calculation looks different from IsLeapYear since y1, y4,
// and y100 are relative to year 1, not year 0
bool leapYear = (y1 == 3 && (y4 != 24 || y100 == 3));
int[] days = leapYear? DaysToMonth366: DaysToMonth365;
// All months have less than 32 days, so n >> 5 is a good conservative
// estimate for the month
int m = n >> 5 + 1;
// m = 1-based month number
while (n >= days[m]) m++;
// If month was requested, return it
if (part == DatePartMonth) return (m);
// Return 1-based day-of-month
return (n - days[m - 1] + 1);
}
