private void updateDataAccordingProlepticSetting() throws Exception {
    for (int i = 0; i < vector.length; i++) {
      if (vector[i] >= CalendarUtils.SWITCHOVER_DAYS) { // no need for conversion
        continue;
      }
      vector[i] = usingProlepticCalendar ? CalendarUtils.convertDateToProleptic((int) vector[i]) : CalendarUtils
          .convertDateToHybrid((int) vector[i]);
    }
  }
Change the calendar to or from proleptic. If the new and old values of the flag are the same,
nothing is done. useProleptic - set the flag for the proleptic calendar updateData - change the
data to match the new value of the flag.
storage-api/src/java/org/apache/hadoop/hive/ql/exec/vector/DateColumnVector.java