public long addMonthsToMillis(long millis, int months) {
    calUtc.setTimeInMillis(millis);
    calUtc.add(Calendar.MONTH, months);
    return calUtc.getTimeInMillis();
  }
Perform month arithmetic to millis value using UTC time zone.
@param millis
@param months
@return
ql/src/java/org/apache/hadoop/hive/ql/util/DateTimeMath.java