code: static JulianDate ofEpochDay(final long epochDay) {
          EPOCH_DAY.range().checkValidValue(epochDay, EPOCH_DAY);  // validate outer bounds
          // use of Julian 0001 makes leap year at end of cycle
          long julianEpochDay = epochDay + JULIAN_0001_TO_ISO_1970;
          long cycle = Math.floorDiv(julianEpochDay, DAYS_PER_CYCLE);
          long daysInCycle = Math.floorMod(julianEpochDay, DAYS_PER_CYCLE);
          if (daysInCycle == DAYS_PER_CYCLE - 1) {
              int year = (int) ((cycle * 4 + 3) + 1);
              return ofYearDay(year, 366);
          }
          int year = (int) ((cycle * 4 + daysInCycle / 365) + 1);
          int doy = (int) ((daysInCycle % 365) + 1);
          return ofYearDay(year, doy);
      }
docs: Obtains a {@code JulianDate} representing a date in the Julian calendar
  system from the epoch-day.
  
  @param epochDay  the epoch day to convert based on 1970-01-01 (ISO)
  @return the date in Julian calendar system, not null
  @throws DateTimeException if the epoch-day is out of range