org.apache.hadoop.util.hash.Hash Maven / Gradle / Ivy
/**
* 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 length, 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);
}