protected void increment(PercentileAgg s, U input, long i) {
      if (s.counts == null) {
        s.counts = new HashMap<U, LongWritable>();
      }
      LongWritable count = s.counts.get(input);
      if (count == null) {
        s.counts.put(copyInput(input), new LongWritable(i));
      } else {
        count.set(count.get() + i);
      }
    }
A state class to store intermediate aggregation results.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFPercentileCont.java