aherbert commented on a change in pull request #131: Added caching hasher URL: https://github.com/apache/commons-collections/pull/131#discussion_r387515514
########## 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> Review comment: A bit more doc would help here, i.e. the List<long[]> will contains zero or more entries, each entry is a non-null array of length two containing the 64-bit pair output from the cyclic hash function. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
