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 
26 package com.google.common.hash;
27 
28 import static com.google.common.primitives.UnsignedBytes.toInt;
29 
30 import com.google.common.primitives.Chars;
31 import com.google.common.primitives.Ints;
32 import com.google.common.primitives.Longs;
33 
34 import java.io.Serializable;
35 import java.nio.ByteBuffer;
36 
37 import javax.annotation.Nullable;
38 
39 /**
40  * See http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp
41  * MurmurHash3_x86_32
42  *
43  * @author Austin Appleby
44  * @author Dimitris Andreou
45  * @author Kurt Alfred Kluever
46  */
47 final class Murmur3_32HashFunction extends AbstractStreamingHashFunction implements Serializable {
48   private static final int C1 = 0xcc9e2d51;
49   private static final int C2 = 0x1b873593;
50 
51   private final int seed;
52 
Murmur3_32HashFunction(int seed)53   Murmur3_32HashFunction(int seed) {
54     this.seed = seed;
55   }
56 
bits()57   @Override public int bits() {
58     return 32;
59   }
60 
newHasher()61   @Override public Hasher newHasher() {
62     return new Murmur3_32Hasher(seed);
63   }
64 
65   @Override
toString()66   public String toString() {
67     return "Hashing.murmur3_32(" + seed + ")";
68   }
69 
70   @Override
equals(@ullable Object object)71   public boolean equals(@Nullable Object object) {
72     if (object instanceof Murmur3_32HashFunction) {
73       Murmur3_32HashFunction other = (Murmur3_32HashFunction) object;
74       return seed == other.seed;
75     }
76     return false;
77   }
78 
79   @Override
hashCode()80   public int hashCode() {
81     return getClass().hashCode() ^ seed;
82   }
83 
hashInt(int input)84   @Override public HashCode hashInt(int input) {
85     int k1 = mixK1(input);
86     int h1 = mixH1(seed, k1);
87 
88     return fmix(h1, Ints.BYTES);
89   }
90 
hashLong(long input)91   @Override public HashCode hashLong(long input) {
92     int low = (int) input;
93     int high = (int) (input >>> 32);
94 
95     int k1 = mixK1(low);
96     int h1 = mixH1(seed, k1);
97 
98     k1 = mixK1(high);
99     h1 = mixH1(h1, k1);
100 
101     return fmix(h1, Longs.BYTES);
102   }
103 
104   // TODO(user): Maybe implement #hashBytes instead?
hashString(CharSequence input)105   @Override public HashCode hashString(CharSequence input) {
106     int h1 = seed;
107 
108     // step through the CharSequence 2 chars at a time
109     for (int i = 1; i < input.length(); i += 2) {
110       int k1 = input.charAt(i - 1) | (input.charAt(i) << 16);
111       k1 = mixK1(k1);
112       h1 = mixH1(h1, k1);
113     }
114 
115     // deal with any remaining characters
116     if ((input.length() & 1) == 1) {
117       int k1 = input.charAt(input.length() - 1);
118       k1 = mixK1(k1);
119       h1 ^= k1;
120     }
121 
122     return fmix(h1, Chars.BYTES * input.length());
123   }
124 
mixK1(int k1)125   private static int mixK1(int k1) {
126     k1 *= C1;
127     k1 = Integer.rotateLeft(k1, 15);
128     k1 *= C2;
129     return k1;
130   }
131 
mixH1(int h1, int k1)132   private static int mixH1(int h1, int k1) {
133     h1 ^= k1;
134     h1 = Integer.rotateLeft(h1, 13);
135     h1 = h1 * 5 + 0xe6546b64;
136     return h1;
137   }
138 
139   // Finalization mix - force all bits of a hash block to avalanche
fmix(int h1, int length)140   private static HashCode fmix(int h1, int length) {
141     h1 ^= length;
142     h1 ^= h1 >>> 16;
143     h1 *= 0x85ebca6b;
144     h1 ^= h1 >>> 13;
145     h1 *= 0xc2b2ae35;
146     h1 ^= h1 >>> 16;
147     return HashCode.fromInt(h1);
148   }
149 
150   private static final class Murmur3_32Hasher extends AbstractStreamingHasher {
151     private static final int CHUNK_SIZE = 4;
152     private int h1;
153     private int length;
154 
Murmur3_32Hasher(int seed)155     Murmur3_32Hasher(int seed) {
156       super(CHUNK_SIZE);
157       this.h1 = seed;
158       this.length = 0;
159     }
160 
process(ByteBuffer bb)161     @Override protected void process(ByteBuffer bb) {
162       int k1 = Murmur3_32HashFunction.mixK1(bb.getInt());
163       h1 = Murmur3_32HashFunction.mixH1(h1, k1);
164       length += CHUNK_SIZE;
165     }
166 
processRemaining(ByteBuffer bb)167     @Override protected void processRemaining(ByteBuffer bb) {
168       length += bb.remaining();
169       int k1 = 0;
170       for (int i = 0; bb.hasRemaining(); i += 8) {
171         k1 ^= toInt(bb.get()) << i;
172       }
173       h1 ^= Murmur3_32HashFunction.mixK1(k1);
174     }
175 
makeHash()176     @Override public HashCode makeHash() {
177       return Murmur3_32HashFunction.fmix(h1, length);
178     }
179   }
180 
181   private static final long serialVersionUID = 0L;
182 }
183