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
15package com.google.common.hash;
16
17import static com.google.common.primitives.UnsignedBytes.toInt;
18
19import java.io.Serializable;
20import java.nio.ByteBuffer;
21
22/**
23 * See http://smhasher.googlecode.com/svn/trunk/MurmurHash3.cpp
24 * MurmurHash3_x86_32
25 *
26 * @author aappleby@google.com (Austin Appleby)
27 * @author andreou@google.com (Dimitris Andreou)
28 */
29final class Murmur3_32HashFunction extends AbstractStreamingHashFunction implements Serializable {
30  private final int seed;
31
32  Murmur3_32HashFunction(int seed) {
33    this.seed = seed;
34  }
35
36  @Override public int bits() {
37    return 32;
38  }
39
40  @Override public Hasher newHasher() {
41    return new Murmur3_32Hasher(seed);
42  }
43
44  private static final class Murmur3_32Hasher extends AbstractStreamingHasher {
45    int h1;
46    int c1 = 0xcc9e2d51;
47    int c2 = 0x1b873593;
48    int len;
49
50    Murmur3_32Hasher(int seed) {
51      super(4);
52      h1 = seed;
53    }
54
55    @Override protected void process(ByteBuffer bb) {
56      int k1 = bb.getInt();
57      len += 4;
58
59      k1 *= c1;
60      k1 = Integer.rotateLeft(k1, 15);
61      k1 *= c2;
62
63      h1 ^= k1;
64      h1 = Integer.rotateLeft(h1, 13);
65      h1 = h1 * 5 + 0xe6546b64;
66    }
67
68    @Override protected void processRemaining(ByteBuffer bb) {
69      len += bb.remaining();
70      int k1 = 0;
71      switch (bb.remaining()) {
72        case 3:
73          k1 ^= toInt(bb.get(2)) << 16;
74          // fall through
75        case 2:
76          k1 ^= toInt(bb.get(1)) << 8;
77          // fall through
78        case 1:
79          k1 ^= toInt(bb.get(0));
80          // fall through
81        default:
82          k1 *= c1;
83          k1 = Integer.rotateLeft(k1, 15);
84          k1 *= c2;
85          h1 ^= k1;
86      }
87    }
88
89    @Override public HashCode makeHash() {
90      h1 ^= len;
91
92      h1 ^= h1 >>> 16;
93      h1 *= 0x85ebca6b;
94      h1 ^= h1 >>> 13;
95      h1 *= 0xc2b2ae35;
96      h1 ^= h1 >>> 16;
97
98      return HashCodes.fromInt(h1);
99    }
100  }
101
102  private static final long serialVersionUID = 0L;
103}
104