public long addMonthsToNanos(long nanos, int months) {
    long result = addMonthsToMillis(nanos / 1000000, months) * 1000000 + (nanos % 1000000);
    return result;
  }
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