@Override
  public int computeEnd(int rowIdx, PTFPartition p) throws HiveException {
    switch(end.getDirection()) {
    case PRECEDING:
      throw new HiveException(
              "PRECEDING not allowed for finishing RANGE with multiple expressions in ORDER BY");
    case CURRENT:
      return computeEndCurrentRow(rowIdx, p);
    case FOLLOWING:
      default:
        return computeEndFollowing(rowIdx, p);
    }
  }
Simply returns the Object[] returned by VectorPTFGroupBatches.getAt(i), which contains the
value of the ordering columns.
ql/src/java/org/apache/hadoop/hive/ql/udf/ptf/ValueBoundaryScanner.java