void Ephemeris::ToJulianDate(DateTime epoch, double& julianDate)
{
int y = epoch.Month <= 2 ? epoch.Year - 1 : epoch.Year;
int m = epoch.Month <= 2 ? epoch.Month + 12 : epoch.Month;
/*
* The reason for the peculiar definition of B are to account for the "lost days" in October 1582
* when the Gregorian Calendar replaced the Julian Calendar in Europe, and to deal with the
* introduction of a leap day in the Gregorian calendar.
*/
int B;
if (epoch.Year < 1582)
{
B = -2;
}
else if (epoch.Year == 1582 && epoch.Month < 10)
{
B = -2;
}
else if (epoch.Year == 1582 && epoch.Month == 10 && epoch.Day <= 4)
{
B = -2;
}
else
{
B = MyInt(y / 400.0) - MyInt(y / 100.0);
}
double universalTime = epoch.Millisec / 3600000.0 + epoch.Second / 3600.0 + epoch.Minute / 60.0 + epoch.Hour;
julianDate = MyInt(365.25 * y) + MyInt(30.6001 * (m + 1)) + B + 1720996.5 + epoch.Day + universalTime / 24.0;
}
inline MyInt operator-(const MyInt& rhs) { return MyInt(-rhs.val); }
void Ephemeris::ToDateTime(double julianDate, DateTime& dateTime)
{
long a = MyInt(julianDate + 0.5);
long b = 0;
long c = 0;
if (a < 2299161)
{
b = 0;
c = a + 1524;
}
if (a >= 2299161)
{
b = MyInt((a - 1867216.25) / 36524.25);
c = a + b - MyInt(b / 4.0) + 1525;
}
long d = MyInt((c - 122.1) / 365.25);
long e = MyInt(365.25 * d);
long f = MyInt((c - e) / 30.6001);
double day = c - e - MyInt(30.6001 * f) + MyFrac(julianDate + 0.5);
int month = (f - 1 - 12 * MyInt(f / 14.0));
int year = (d - 4715 - MyInt((7 + month) / 10.0));
double universalTime = MyFrac(day) * 24.0;
int hour = MyInt(universalTime);
double r = MyFrac(universalTime) * 60.0;
int minute = MyInt(r);
r = MyFrac(r) * 60;
int second = MyInt(r);
dateTime.Year = year;
dateTime.Month = month;
dateTime.Day = MyInt(day);
dateTime.Hour = hour;
dateTime.Minute = minute;
dateTime.Second = second;
}