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.classification.InterfaceAudience;
23 import org.apache.hadoop.classification.InterfaceStability;
24 import org.apache.hadoop.conf.Configuration;
25
26 /**
27 * This class represents a common API for hashing functions.
28 */
29 @InterfaceAudience.Public
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
39 /**
40 * This utility method converts String representation of hash function name
41 * to a symbolic constant. Currently two function types are supported,
42 * "jenkins" and "murmur".
43 * @param name hash function name
44 * @return one of the predefined constants
45 */
46 public static int parseHashType(String name) {
47 if ("jenkins".equalsIgnoreCase(name)) {
48 return JENKINS_HASH;
49 } else if ("murmur".equalsIgnoreCase(name)) {
50 return MURMUR_HASH;
51 } else {
52 return INVALID_HASH;
53 }
54 }
55
56 /**
57 * This utility method converts the name of the configured
58 * hash type to a symbolic constant.
59 * @param conf configuration
60 * @return one of the predefined constants
61 */
62 public static int getHashType(Configuration conf) {
63 String name = conf.get("hbase.hash.type", "murmur");
64 return parseHashType(name);
65 }
66
67 /**
68 * Get a singleton instance of hash function of a given type.
69 * @param type predefined hash type
70 * @return hash function instance, or null if type is invalid
71 */
72 public static Hash getInstance(int type) {
73 switch(type) {
74 case JENKINS_HASH:
75 return JenkinsHash.getInstance();
76 case MURMUR_HASH:
77 return MurmurHash.getInstance();
78 default:
79 return null;
80 }
81 }
82
83 /**
84 * Get a singleton instance of hash function of a type
85 * defined in the configuration.
86 * @param conf current configuration
87 * @return defined hash type, or null if type is invalid
88 */
89 public static Hash getInstance(Configuration conf) {
90 int type = getHashType(conf);
91 return getInstance(type);
92 }
93
94 /**
95 * Calculate a hash using all bytes from the input argument, and
96 * a seed of -1.
97 * @param bytes input bytes
98 * @return hash value
99 */
100 public int hash(byte[] bytes) {
101 return hash(bytes, bytes.length, -1);
102 }
103
104 /**
105 * Calculate a hash using all bytes from the input argument,
106 * and a provided seed value.
107 * @param bytes input bytes
108 * @param initval seed value
109 * @return hash value
110 */
111 public int hash(byte[] bytes, int initval) {
112 return hash(bytes, 0, bytes.length, initval);
113 }
114
115 /**
116 * Calculate a hash using bytes from 0 to <code>length</code>, and
117 * the provided seed value
118 * @param bytes input bytes
119 * @param length length of the valid bytes after offset to consider
120 * @param initval seed value
121 * @return hash value
122 */
123 public int hash(byte[] bytes, int length, int initval) {
124 return hash(bytes, 0, length, initval);
125 }
126
127 /**
128 * Calculate a hash using bytes from <code>offset</code> to <code>offset +
129 * length</code>, and the provided seed value.
130 * @param bytes input bytes
131 * @param offset the offset into the array to start consideration
132 * @param length length of the valid bytes after offset to consider
133 * @param initval seed value
134 * @return hash value
135 */
136 public abstract int hash(byte[] bytes, int offset, int length, int initval);
137 }