aherbert commented on a change in pull request #131: Added caching hasher URL: https://github.com/apache/commons-collections/pull/131#discussion_r387516238
########## File path: src/main/java/org/apache/commons/collections4/bloomfilter/hasher/CachingHasher.java ########## @@ -0,0 +1,233 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ +package org.apache.commons.collections4.bloomfilter.hasher; + +import java.nio.charset.StandardCharsets; +import java.util.ArrayList; +import java.util.Arrays; +import java.util.List; +import java.util.NoSuchElementException; +import java.util.PrimitiveIterator; + +import org.apache.commons.collections4.bloomfilter.hasher.HashFunctionIdentity.ProcessType; + +/** + * An implementation of Hasher that attempts to leak as little data as possible. + * Each item in the hasher is represented by two (2) longs. So this Hasher will + * still indicate how many items are in the hasher but will not leak the buffers + * that are being hashed as the @code DynamicHasher} does. + * <p> + * This hasher only accepts HashFunctions that are cyclic in nature. + * </p> + * @see DynamicHasher + * @see ProcessType + */ +public class CachingHasher implements Hasher { + + /** + * The list of byte arrays that are to be hashed. + */ + private final List<long[]> buffers; + + /** + * The hash function identity + */ + private final HashFunctionIdentity functionIdentity; + + /** + * Constructs a CachingHasher from a list of arrays of hash values. + * <p> + * The list of hash values comprises a @code{List<long[]>} where each @code{long[]} + * is comprises two (2) values that are the result of hashing the original buffer. Thus a + * CachingHasher that was built from five (5) buffers will have five arrays of two @code{longs} + * each. + * </p> + * @param functionIdentity The identity of the function. + * @param buffers a list of @code{long} arrays comprising two (2) values. + * @throws IllegalArgumentException if the name does not indicate a cyclic + * hashing function. + */ + public CachingHasher(HashFunctionIdentity functionIdentity, List<long[]> buffers) { + this.functionIdentity = checkIdentity(functionIdentity); + this.buffers = new ArrayList<long[]>(buffers); + } + + /** + * Constructs a CachingHasher from an array of arrys of hash values. + * + * @param functionIdentity The identity of the function. + * @param buffers an array of @code{long} arrays comprising two (2) values. + * @throws IllegalArgumentException if the name does not indicate a cyclic + * hashing function. + */ + public CachingHasher(HashFunctionIdentity functionIdentity, long[][] buffers) { + this.functionIdentity = checkIdentity(functionIdentity); + this.buffers = Arrays.asList(buffers); + } + + /** + * Checks that the name is valid for this hasher. + * + * @param functionIdentity the Function Identity to check. + */ + private static HashFunctionIdentity checkIdentity(HashFunctionIdentity functionIdentity) { + if (functionIdentity.getProcessType() != ProcessType.CYCLIC) { + throw new IllegalArgumentException("Only cyclic hash functions may be used in a caching hasher"); + } + return functionIdentity; + } + + @Override + public HashFunctionIdentity getHashFunctionIdentity() { + return functionIdentity; + } + + @Override + public boolean isEmpty() { + return buffers.isEmpty(); + } + + + @Override + public PrimitiveIterator.OfInt getBits(Shape shape) { + HashFunctionValidator.checkAreEqual(getHashFunctionIdentity(), + shape.getHashFunctionIdentity()); + return new IntIterator(shape); + } + + /** + * Gets the long representations of the buffers. + * <p> + * This method returns the long representations of the buffers. This is commonly used + * to transmit the Hasher from one system to another. + * </p> + * @return a copy if the long buffer representation. + */ + public List<long[]> getBuffers() { + return new ArrayList<long[]>( buffers ); + } + + /** + * The iterator of integers. + */ + private class IntIterator implements PrimitiveIterator.OfInt { + private int buffer = 0; + private int funcCount = 0; + private final Shape shape; + private long accumulator; + + /** + * Creates iterator with the specified shape. + * + * @param shape + */ + private IntIterator(Shape shape) { + this.shape = shape; + this.accumulator = buffers.isEmpty() ? 0 : buffers.get(0)[0]; + } + + @Override + public boolean hasNext() { + if (buffers.isEmpty()) { + return false; + } + return buffer < buffers.size() - 1 || funcCount < shape.getNumberOfHashFunctions(); + } + + @Override + public int nextInt() { + if (hasNext()) { + if (funcCount >= shape.getNumberOfHashFunctions()) { + funcCount = 0; + buffer++; + accumulator = buffers.get(buffer)[0]; + } + int result = (int) Math.floorMod(accumulator, (long) shape.getNumberOfBits()); + funcCount++; + accumulator += buffers.get(buffer)[1]; + return result; + } + throw new NoSuchElementException(); + } + + } + + /** + * The builder for CachingHashers. + * + * @since 4.5 + */ + public static class Builder implements Hasher.Builder { + /** + * The list of byte[] that are to be hashed. + */ + private List<byte[]> buffers; + + /** + * The function that the resulting DynamicHasher will use. + */ + private HashFunction function; + + /** + * Constructs a CachingHashers builder. + * + * @param function the function implementation. + * @throws IllegalArgumentException if the function is not a cyclic implementation. + */ + public Builder(HashFunction function) { + checkIdentity(function); + this.function = function; + this.buffers = new ArrayList<byte[]>(); + + } + + /** + * Builds the hasher. + * + * @return A CachingHashers with the specified name, function and buffers. + */ + @Override + public CachingHasher build() throws IllegalArgumentException { + List<long[]> cache = new ArrayList<long[]>(); Review comment: use final ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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