Murmur3_32HashFunction.java revision 7dd252788645e940eada959bdde927426e2531c9 
1/*
2 * Copyright (C) 2011 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15/*
16 * MurmurHash3 was written by Austin Appleby, and is placed in the public
17 * domain. The author hereby disclaims copyright to this source code.
18 */
19
20/*
21 * Source:
22 * http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
23 * (Modified to adapt to Guava coding conventions and to use the HashFunction interface)
24 */
25
26package com.google.common.hash;
27
28import static com.google.common.primitives.UnsignedBytes.toInt;
29
30import com.google.common.primitives.Chars;
31import com.google.common.primitives.Ints;
32import com.google.common.primitives.Longs;
33
34import java.io.Serializable;
35import java.nio.ByteBuffer;
36
37/**
38 * See http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp
39 * MurmurHash3_x86_32
40 *
41 * @author Austin Appleby
42 * @author Dimitris Andreou
43 * @author Kurt Alfred Kluever
44 */
45final class Murmur3_32HashFunction extends AbstractStreamingHashFunction implements Serializable {
46  private static final int C1 = 0xcc9e2d51;
47  private static final int C2 = 0x1b873593;
48
49  private final int seed;
50
51  Murmur3_32HashFunction(int seed) {
52    this.seed = seed;
53  }
54
55  public int bits() {
56    return 32;
57  }
58
59  public Hasher newHasher() {
60    return new Murmur3_32Hasher(seed);
61  }
62
63  @Override
64  public String toString() {
65    return "Hashing.murmur3_32(" + seed + ")";
66  }
67
68  @Override public HashCode hashInt(int input) {
69    int k1 = mixK1(input);
70    int h1 = mixH1(seed, k1);
71
72    return fmix(h1, Ints.BYTES);
73  }
74
75  @Override
76  public HashCode hashLong(long input) {
77    int low = (int) input;
78    int high = (int) (input >>> 32);
79
80    int k1 = mixK1(low);
81    int h1 = mixH1(seed, k1);
82
83    k1 = mixK1(high);
84    h1 = mixH1(h1, k1);
85
86    return fmix(h1, Longs.BYTES);
87  }
88
89  // TODO(user): Maybe implement #hashBytes instead?
90  @Override
91  public HashCode hashString(CharSequence input) {
92    int h1 = seed;
93
94    // step through the CharSequence 2 chars at a time
95    for (int i = 1; i < input.length(); i += 2) {
96      int k1 = input.charAt(i - 1) | (input.charAt(i) << 16);
97      k1 = mixK1(k1);
98      h1 = mixH1(h1, k1);
99    }
100
101    // deal with any remaining characters
102    if ((input.length() & 1) == 1) {
103      int k1 = input.charAt(input.length() - 1);
104      k1 = mixK1(k1);
105      h1 ^= k1;
106    }
107
108    return fmix(h1, Chars.BYTES * input.length());
109  }
110
111  private static int mixK1(int k1) {
112    k1 *= C1;
113    k1 = Integer.rotateLeft(k1, 15);
114    k1 *= C2;
115    return k1;
116  }
117
118  private static int mixH1(int h1, int k1) {
119    h1 ^= k1;
120    h1 = Integer.rotateLeft(h1, 13);
121    h1 = h1 * 5 + 0xe6546b64;
122    return h1;
123  }
124
125  // Finalization mix - force all bits of a hash block to avalanche
126  private static HashCode fmix(int h1, int length) {
127    h1 ^= length;
128    h1 ^= h1 >>> 16;
129    h1 *= 0x85ebca6b;
130    h1 ^= h1 >>> 13;
131    h1 *= 0xc2b2ae35;
132    h1 ^= h1 >>> 16;
133    return HashCodes.fromInt(h1);
134  }
135
136  private static final class Murmur3_32Hasher extends AbstractStreamingHasher {
137    private static final int CHUNK_SIZE = 4;
138    private int h1;
139    private int length;
140
141    Murmur3_32Hasher(int seed) {
142      super(CHUNK_SIZE);
143      this.h1 = seed;
144      this.length = 0;
145    }
146
147    @Override
148    protected void process(ByteBuffer bb) {
149      int k1 = Murmur3_32HashFunction.mixK1(bb.getInt());
150      h1 = Murmur3_32HashFunction.mixH1(h1, k1);
151      length += CHUNK_SIZE;
152    }
153
154    @Override
155    protected void processRemaining(ByteBuffer bb) {
156      length += bb.remaining();
157      int k1 = 0;
158      for (int i = 0; bb.hasRemaining(); i += 8) {
159        k1 ^= toInt(bb.get()) << i;
160      }
161      h1 ^= Murmur3_32HashFunction.mixK1(k1);
162    }
163
164    @Override
165    public HashCode makeHash() {
166      return Murmur3_32HashFunction.fmix(h1, length);
167    }
168  }
169
170  private static final long serialVersionUID = 0L;
171}
172