@Override
  public void writeFieldEnd() throws TException {
    if (stackLevel == 1) {
      topLevelStructFieldID++;
      ascending = (topLevelStructFieldID >= sortOrder.length() || sortOrder
          .charAt(topLevelStructFieldID) != '-');
    }
  }
Whether the current field is sorted ascendingly. Always equals to
sortOrder.charAt(topLevelStructFieldID) != '-'
serde/src/java/org/apache/hadoop/hive/serde2/thrift/TBinarySortableProtocol.java