Method homogeneousUnion

src/main/java/net/agkn/hll/HLL.java:818–857

Computes the union of two HLLs of the same type, and stores the result in this instance. @param other the other HLL instance to union into this one. This cannot be null .

(final HLL other)

     *        cannot be <code>null</code>.
     */
    private void homogeneousUnion(final HLL other) {
        switch(type) {
            case EMPTY:
                // union of empty and empty is empty
                return;
        case EXPLICIT:
            for(final long value : other.explicitStorage) {
                addRaw(value);
            }
            // NOTE:  #addRaw() will handle promotion, if necessary
            return;
        case SPARSE:
            for(final int registerIndex : other.sparseProbabilisticStorage.keySet()) {
                final byte registerValue = other.sparseProbabilisticStorage.get(registerIndex);
                final byte currentRegisterValue = sparseProbabilisticStorage.get(registerIndex);
                if(registerValue > currentRegisterValue) {
                    sparseProbabilisticStorage.put(registerIndex, registerValue);
                }
            }

            // promotion, if necessary
            if(sparseProbabilisticStorage.size() > sparseThreshold) {
                initializeStorage(HLLType.FULL);
                for(final int registerIndex : sparseProbabilisticStorage.keySet()) {
                    final byte registerValue = sparseProbabilisticStorage.get(registerIndex);
                    probabilisticStorage.setMaxRegister(registerIndex, registerValue);
                }
                sparseProbabilisticStorage = null;
            }
            return;
        case FULL:
            for(int i=0; i<m; i++) {
                final long registerValue = other.probabilisticStorage.getRegister(i);
                probabilisticStorage.setMaxRegister(i, registerValue);
            }
            return;
        default:
                throw new RuntimeException("Unsupported HLL type " + type);
        }
    }

    // ========================================================================
    // Serialization