code: public long cardinality() {
          switch(type) {
              case EMPTY:
                  return 0/*by definition*/;
              case EXPLICIT:
                  return explicitStorage.size();
              case SPARSE:
                  return (long)Math.ceil(sparseProbabilisticAlgorithmCardinality());
              case FULL:
                  return (long)Math.ceil(fullProbabilisticAlgorithmCardinality());
              default:
                  throw new RuntimeException("Unsupported HLL type " + type);
          }
      }
docs: Computes the cardinality of the HLL.
  
  @return the cardinality of HLL. This will never be negative.