public SketchFunctionDescriptor getSketchFunction(String className, String function) {
    if (!sketchClasses.containsKey(className)) {
      throw new IllegalArgumentException(String.format("Sketch-class '%s' doesn't exists", className));
    }
    SketchDescriptor sc = sketchClasses.get(className);
    if (!sc.fnMap.containsKey(function)) {
      throw new IllegalArgumentException(
          String.format("The Sketch-class '%s' doesn't have a '%s' method", className, function));
    }
    return sketchClasses.get(className).fnMap.get(function);
  }
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