[GitHub] [commons-collections] Claudenw commented on a change in pull request #131: WIP: Added caching hasher

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Claudenw commented on a change in pull request #131: WIP: Added caching hasher
URL: https://github.com/apache/commons-collections/pull/131#discussion_r381572097
 
 

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 File path: src/main/java/org/apache/commons/collections4/bloomfilter/hasher/CachingHasher.java
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+/*
+ * 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.HashFunction;
+import org.apache.commons.collections4.bloomfilter.hasher.HashFunctionIdentity;
+import org.apache.commons.collections4.bloomfilter.hasher.Hasher;
+import org.apache.commons.collections4.bloomfilter.hasher.Shape;
+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&lt;long[]&gt;} 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.
+     *
+     * @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);
+    }
+
+    /**
+     * Check that the name is valid for this hasher.
 
 Review comment:
   fixed.

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