code: private BaseCalendar.Date getCalendarDate(long fd) {
          BaseCalendar cal = (fd >= gregorianCutoverDate) ? gcal : getJulianCalendarSystem();
          BaseCalendar.Date d = (BaseCalendar.Date) cal.newCalendarDate(TimeZone.NO_TIMEZONE);
          cal.getCalendarDateFromFixedDate(d, fd);
          return d;
      }
docs: Returns a CalendarDate produced from the specified fixed date.
  
  @param fd the fixed date