private void registerHll() {
    SketchDescriptor sd = new SketchDescriptor("hll");
    sd.register(DATA_TO_SKETCH, org.apache.datasketches.hive.hll.DataToSketchUDAF.class);
    sd.register(SKETCH_TO_ESTIMATE_WITH_ERROR_BOUNDS,
        org.apache.datasketches.hive.hll.SketchToEstimateAndErrorBoundsUDF.class);
    sd.register(SKETCH_TO_ESTIMATE, org.apache.datasketches.hive.hll.SketchToEstimateUDF.class);
    sd.register(SKETCH_TO_STRING, org.apache.datasketches.hive.hll.SketchToStringUDF.class);
    sd.register(UNION_SKETCH1, org.apache.datasketches.hive.hll.UnionSketchUDF.class);
    sd.register(UNION_SKETCH, org.apache.datasketches.hive.hll.UnionSketchUDAF.class);
    sketchClasses.put("hll", sd);
  }
Registers functions from the DataSketches library as builtin functions.

In an effort to show a more consistent
ql/src/java/org/apache/hadoop/hive/ql/exec/DataSketchesFunctions.java