1 /**
2 *
3 * Licensed to the Apache Software Foundation (ASF) under one
4 * or more contributor license agreements. See the NOTICE file
5 * distributed with this work for additional information
6 * regarding copyright ownership. The ASF licenses this file
7 * to you under the Apache License, Version 2.0 (the
8 * "License"); you may not use this file except in compliance
9 * with the License. You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 */
19
20 package org.apache.hadoop.hbase.util;
21
22 import org.apache.hadoop.hbase.classification.InterfaceAudience;
23 import org.apache.hadoop.hbase.classification.InterfaceStability;
24 import org.apache.hadoop.conf.Configuration;
25
26 /**
27 * This class represents a common API for hashing functions.
28 */
29 @InterfaceAudience.Private
30 @InterfaceStability.Stable
31 public abstract class Hash {
32 /** Constant to denote invalid hash type. */
33 public static final int INVALID_HASH = -1;
34 /** Constant to denote {@link JenkinsHash}. */
35 public static final int JENKINS_HASH = 0;
36 /** Constant to denote {@link MurmurHash}. */
37 public static final int MURMUR_HASH = 1;
38 /** Constant to denote {@link MurmurHash3}. */
39 public static final int MURMUR_HASH3 = 2;
40
41 /**
42 * This utility method converts String representation of hash function name
43 * to a symbolic constant. Currently three function types are supported,
44 * "jenkins", "murmur" and "murmur3".
45 * @param name hash function name
46 * @return one of the predefined constants
47 */
48 public static int parseHashType(String name) {
49 if ("jenkins".equalsIgnoreCase(name)) {
50 return JENKINS_HASH;
51 } else if ("murmur".equalsIgnoreCase(name)) {
52 return MURMUR_HASH;
53 } else if ("murmur3".equalsIgnoreCase(name)) {
54 return MURMUR_HASH3;
55 } else {
56 return INVALID_HASH;
57 }
58 }
59
60 /**
61 * This utility method converts the name of the configured
62 * hash type to a symbolic constant.
63 * @param conf configuration
64 * @return one of the predefined constants
65 */
66 public static int getHashType(Configuration conf) {
67 String name = conf.get("hbase.hash.type", "murmur");
68 return parseHashType(name);
69 }
70
71 /**
72 * Get a singleton instance of hash function of a given type.
73 * @param type predefined hash type
74 * @return hash function instance, or null if type is invalid
75 */
76 public static Hash getInstance(int type) {
77 switch(type) {
78 case JENKINS_HASH:
79 return JenkinsHash.getInstance();
80 case MURMUR_HASH:
81 return MurmurHash.getInstance();
82 case MURMUR_HASH3:
83 return MurmurHash3.getInstance();
84 default:
85 return null;
86 }
87 }
88
89 /**
90 * Get a singleton instance of hash function of a type
91 * defined in the configuration.
92 * @param conf current configuration
93 * @return defined hash type, or null if type is invalid
94 */
95 public static Hash getInstance(Configuration conf) {
96 int type = getHashType(conf);
97 return getInstance(type);
98 }
99
100 /**
101 * Calculate a hash using all bytes from the input argument, and
102 * a seed of -1.
103 * @param bytes input bytes
104 * @return hash value
105 */
106 public int hash(byte[] bytes) {
107 return hash(bytes, bytes.length, -1);
108 }
109
110 /**
111 * Calculate a hash using all bytes from the input argument,
112 * and a provided seed value.
113 * @param bytes input bytes
114 * @param initval seed value
115 * @return hash value
116 */
117 public int hash(byte[] bytes, int initval) {
118 return hash(bytes, 0, bytes.length, initval);
119 }
120
121 /**
122 * Calculate a hash using bytes from 0 to <code>length</code>, and
123 * the provided seed value
124 * @param bytes input bytes
125 * @param length length of the valid bytes after offset to consider
126 * @param initval seed value
127 * @return hash value
128 */
129 public int hash(byte[] bytes, int length, int initval) {
130 return hash(bytes, 0, length, initval);
131 }
132
133 /**
134 * Calculate a hash using bytes from <code>offset</code> to <code>offset +
135 * length</code>, and the provided seed value.
136 * @param bytes input bytes
137 * @param offset the offset into the array to start consideration
138 * @param length length of the valid bytes after offset to consider
139 * @param initval seed value
140 * @return hash value
141 */
142 public abstract int hash(byte[] bytes, int offset, int length, int initval);
143 }