Standardise computation of signatures.

src/main/java/org/apache/commons/collections4/bloomfilter/hasher/function/MD5Cyclic.java

@@ -22,7 +22,6 @@ import java.nio.LongBuffer;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import org.apache.commons.collections4.bloomfilter.hasher.HashFunction;
-import org.apache.commons.collections4.bloomfilter.hasher.HashFunctionIdentity;
 
 /**
  * An implementation of HashFunction that
@@ -43,6 +42,8 @@ public final class MD5Cyclic implements HashFunction {
 
     /**
      * The signature for this hash function.
+     *
+     * <p>TODO: Make static akin to a serialVersionUID?
      */
     private final long signature;
 
@@ -61,7 +62,7 @@ public final class MD5Cyclic implements HashFunction {
             // This should not happen
             throw new IllegalStateException("Missing the standard MD5 message digest algorithm", e);
         }
-        signature = apply(HashFunctionIdentity.prepareSignatureBuffer(this), 0);
+        signature = Signatures.getSignature(this);
     }
 
     @Override

src/main/java/org/apache/commons/collections4/bloomfilter/hasher/function/Murmur128x86Cyclic.java

@@ -18,7 +18,6 @@ package org.apache.commons.collections4.bloomfilter.hasher.function;
 
 import org.apache.commons.codec.digest.MurmurHash3;
 import org.apache.commons.collections4.bloomfilter.hasher.HashFunction;
-import org.apache.commons.collections4.bloomfilter.hasher.HashFunctionIdentity;
 
 /**
  * An implementation of HashFunction that
@@ -32,6 +31,8 @@ public final class Murmur128x86Cyclic implements HashFunction {
 
     /**
      * The name of this hash method.
+     *
+     * <p>TODO: Should this be changed to "Murmur3_128_x64"?
      */
     public static final String NAME = "Murmur3_x64_128";
 
@@ -42,6 +43,8 @@ public final class Murmur128x86Cyclic implements HashFunction {
 
     /**
      * The signature for this hash function.
+     *
+     * <p>TODO: Make static akin to a serialVersionUID?
      */
     private final long signature;
 
@@ -49,7 +52,7 @@ public final class Murmur128x86Cyclic implements HashFunction {
      * Constructs a Murmur3 x64 128 hash.
      */
     public Murmur128x86Cyclic() {
-        signature = apply(HashFunctionIdentity.prepareSignatureBuffer(this), 0);
+        signature = Signatures.getSignature(this);
     }
 
     @Override

src/main/java/org/apache/commons/collections4/bloomfilter/hasher/function/Murmur32x86Iterative.java

@@ -18,7 +18,6 @@ package org.apache.commons.collections4.bloomfilter.hasher.function;
 
 import org.apache.commons.codec.digest.MurmurHash3;
 import org.apache.commons.collections4.bloomfilter.hasher.HashFunction;
-import org.apache.commons.collections4.bloomfilter.hasher.HashFunctionIdentity;
 
 /**
  * An implementation of HashFunction that
@@ -32,11 +31,15 @@ public final class Murmur32x86Iterative implements HashFunction {
 
     /**
      * The name of this hash function.
+     *
+     * <p>TODO: Should this be changed to "Murmur3_32_x86"?
      */
     public static final String NAME = "Murmur3_x86_32";
 
     /**
      * The signature for this hash function.
+     *
+     * <p>TODO: Make static akin to a serialVersionUID?
      */
     private final long signature;
 
@@ -44,7 +47,7 @@ public final class Murmur32x86Iterative implements HashFunction {
      * Constructs a Murmur3 x86 32 hash
      */
     public Murmur32x86Iterative() {
-        signature = apply(HashFunctionIdentity.prepareSignatureBuffer(this), 0);
+        signature = Signatures.getSignature(this);
     }
 
     @Override

src/main/java/org/apache/commons/collections4/bloomfilter/hasher/function/ObjectsHashIterative.java

@@ -18,7 +18,6 @@ package org.apache.commons.collections4.bloomfilter.hasher.function;
 
 import java.util.Arrays;
 import org.apache.commons.collections4.bloomfilter.hasher.HashFunction;
-import org.apache.commons.collections4.bloomfilter.hasher.HashFunctionIdentity;
 
 /**
  * An implementation of HashFunction that
@@ -39,6 +38,8 @@ public final class ObjectsHashIterative implements HashFunction {
 
     /**
      * The signature for this hash function.
+     *
+     * <p>TODO: Make static akin to a serialVersionUID?
      */
     private final long signature;
 
@@ -51,7 +52,7 @@ public final class ObjectsHashIterative implements HashFunction {
      * Constructs a hash that uses the Objects.hash method to has values.
      */
     public ObjectsHashIterative() {
-        signature = apply(HashFunctionIdentity.prepareSignatureBuffer(this), 0);
+        signature = Signatures.getSignature(this);
     }
 
     @Override

src/main/java/org/apache/commons/collections4/bloomfilter/hasher/function/Signatures.java

@@ -0,0 +1,46 @@
+/*
+ * 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.function;
+
+import org.apache.commons.collections4.bloomfilter.hasher.HashFunction;
+import org.apache.commons.collections4.bloomfilter.hasher.HashFunctionIdentity;
+
+/**
+ * Allow computation of HashFunction signatures.
+ * @since 4.5
+ */
+final class Signatures {
+
+    /** No instances. */
+    private Signatures() {}
+
+    /**
+     * Gets the standard signature for the hash function. The signature is prepared as:
+     * <pre><code>
+     * int seed = 0;
+     * return hashFunction.apply(HashFunctionIdentity.prepareSignatureBuffer(hashFunction), seed);
+     * </code></pre>
+     *
+     * @param hashFunction the hash function
+     * @return the signature
+     * @see HashFunctionIdentity#prepareSignatureBuffer(HashFunctionIdentity)
+     * @see HashFunction#apply(byte[], int)
+     */
+    static long getSignature(HashFunction hashFunction) {
+        return hashFunction.apply(HashFunctionIdentity.prepareSignatureBuffer(hashFunction), 0);
+    }
+}