@Override
    public List<DoubleWritable> convertPercentileParameter(Object parameter) {
      Double percentile = ((HiveDecimalWritable) parameter).getHiveDecimal().doubleValue();
      PercentileContEvaluator.validatePercentile(percentile);
      return singletonList(new DoubleWritable(percentile));
    }
A state class to store intermediate aggregation results.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFPercentileCont.java