HBASE-875 Use MurmurHash instead of JenkinsHash

git-svn-id: https://svn.apache.org/repos/asf/hadoop/hbase/trunk@698268 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/hadoop/hbase/util/Hash.java

@@ -0,0 +1,119 @@
+/**
+ * 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.hadoop.hbase.util;
+
+import org.apache.hadoop.conf.Configuration;
+
+/**
+ * This class represents a common API for hashing functions.
+ */
+public abstract class Hash {
+  /** Constant to denote invalid hash type. */
+  public static final int INVALID_HASH = -1;
+  /** Constant to denote {@link JenkinsHash}. */
+  public static final int JENKINS_HASH = 0;
+  /** Constant to denote {@link MurmurHash}. */
+  public static final int MURMUR_HASH  = 1;
+  
+  /**
+   * This utility method converts String representation of hash function name
+   * to a symbolic constant. Currently two function types are supported,
+   * "jenkins" and "murmur".
+   * @param name hash function name
+   * @return one of the predefined constants
+   */
+  public static int parseHashType(String name) {
+    if ("jenkins".equalsIgnoreCase(name)) {
+      return JENKINS_HASH;
+    } else if ("murmur".equalsIgnoreCase(name)) {
+      return MURMUR_HASH;
+    } else {
+      return INVALID_HASH;
+    }
+  }
+  
+  /**
+   * This utility method converts the name of the configured
+   * hash type to a symbolic constant.
+   * @param conf configuration
+   * @return one of the predefined constants
+   */
+  public static int getHashType(Configuration conf) {
+    String name = conf.get("hbase.hash.type", "murmur");
+    return parseHashType(name);
+  }
+  
+  /**
+   * Get a singleton instance of hash function of a given type.
+   * @param type predefined hash type
+   * @return hash function instance, or null if type is invalid
+   */
+  public static Hash getInstance(int type) {
+    switch(type) {
+    case JENKINS_HASH:
+      return JenkinsHash.getInstance();
+    case MURMUR_HASH:
+      return MurmurHash.getInstance();
+    default:
+      return null;
+    }
+  }
+  
+  /**
+   * Get a singleton instance of hash function of a type
+   * defined in the configuration.
+   * @param conf current configuration
+   * @return defined hash type, or null if type is invalid
+   */
+  public static Hash getInstance(Configuration conf) {
+    int type = getHashType(conf);
+    return getInstance(type);
+  }
+  
+  /**
+   * Calculate a hash using all bytes from the input argument, and
+   * a seed of -1.
+   * @param bytes input bytes
+   * @return hash value
+   */
+  public int hash(byte[] bytes) {
+    return hash(bytes, bytes.length, -1);
+  }
+  
+  /**
+   * Calculate a hash using all bytes from the input argument,
+   * and a provided seed value.
+   * @param bytes input bytes
+   * @param initval seed value
+   * @return hash value
+   */
+  public int hash(byte[] bytes, int initval) {
+    return hash(bytes, bytes.length, initval);
+  }
+  
+  /**
+   * Calculate a hash using bytes from 0 to <code>length</code>, and
+   * the provided seed value
+   * @param bytes input bytes
+   * @param length length of the valid bytes to consider
+   * @param initval seed value
+   * @return
+   */
+  public abstract int hash(byte[] bytes, int length, int initval);
+}

src/java/org/apache/hadoop/hbase/util/MurmurHash.java

@@ -0,0 +1,83 @@
+/**
+ * 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.hadoop.hbase.util;
+
+/**
+ * This is a very fast, non-cryptographic hash suitable for general hash-based
+ * lookup.  See http://murmurhash.googlepages.com/ for more details.
+ * 
+ * <p>The C version of MurmurHash 2.0 found at that site was ported
+ * to Java by Andrzej Bialecki (ab at getopt org).</p>
+ */
+public class MurmurHash extends Hash {
+  private static MurmurHash _instance = new MurmurHash();
+  
+  public static Hash getInstance() {
+    return _instance;
+  }
+  
+  public int hash(byte[] data, int length, int seed) {
+    int m = 0x5bd1e995;
+    int r = 24;
+
+    int h = seed ^ length;
+
+    int len_4 = length >> 2;
+
+    for (int i = 0; i < len_4; i++) {
+      int i_4 = i << 2;
+      int k = data[i_4 + 3];
+      k = k << 8;
+      k = k | (data[i_4 + 2] & 0xff);
+      k = k << 8;
+      k = k | (data[i_4 + 1] & 0xff);
+      k = k << 8;
+      k = k | (data[i_4 + 0] & 0xff);
+      k *= m;
+      k ^= k >>> r;
+      k *= m;
+      h *= m;
+      h ^= k;
+    }
+
+    // avoid calculating modulo
+    int len_m = len_4 << 2;
+    int left = length - len_m;
+
+    if (left != 0) {
+      if (left >= 3) {
+        h ^= (int) data[length - 3] << 16;
+      }
+      if (left >= 2) {
+        h ^= (int) data[length - 2] << 8;
+      }
+      if (left >= 1) {
+        h ^= (int) data[length - 1];
+      }
+
+      h *= m;
+    }
+
+    h ^= h >>> 13;
+    h *= m;
+    h ^= h >>> 15;
+
+    return h;
+  }
+}