| /** |
| * 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.util.hash; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| import org.apache.hadoop.conf.Configuration; |
| |
| /** |
| * This class represents a common API for hashing functions. |
| */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Unstable |
| 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("hadoop.util.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 hash value |
| */ |
| public abstract int hash(byte[] bytes, int length, int initval); |
| } |