1   /*
2    * Copyright (C) 2008 The Guava Authors
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    * http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  package com.google.common.collect;
18  
19  import com.google.common.annotations.GwtCompatible;
20  import com.google.common.primitives.Ints;
21  
22  import javax.annotation.Nullable;
23  
24  /**
25   * Static methods for implementing hash-based collections.
26   *
27   * @author Kevin Bourrillion
28   * @author Jesse Wilson
29   * @author Austin Appleby
30   */
31  @GwtCompatible
32  final class Hashing {
33    private Hashing() {}
34  
35    private static final int C1 = 0xcc9e2d51;
36    private static final int C2 = 0x1b873593;
37  
38    /*
39     * This method was rewritten in Java from an intermediate step of the Murmur hash function in
40     * http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp, which contained the
41     * following header:
42     *
43     * MurmurHash3 was written by Austin Appleby, and is placed in the public domain. The author
44     * hereby disclaims copyright to this source code.
45     */
46    static int smear(int hashCode) {
47      return C2 * Integer.rotateLeft(hashCode * C1, 15);
48    }
49    
50    static int smearedHash(@Nullable Object o) {
51      return smear((o == null) ? 0 : o.hashCode());
52    }
53    
54    private static int MAX_TABLE_SIZE = Ints.MAX_POWER_OF_TWO;
55    
56    static int closedTableSize(int expectedEntries, double loadFactor) {
57      // Get the recommended table size.
58      // Round down to the nearest power of 2.
59      expectedEntries = Math.max(expectedEntries, 2);
60      int tableSize = Integer.highestOneBit(expectedEntries);
61      // Check to make sure that we will not exceed the maximum load factor.
62      if (expectedEntries > (int) (loadFactor * tableSize)) {
63        tableSize <<= 1;
64        return (tableSize > 0) ? tableSize : MAX_TABLE_SIZE;
65      }
66      return tableSize;
67    }
68    
69    static boolean needsResizing(int size, int tableSize, double loadFactor) {
70      return size > loadFactor * tableSize && tableSize < MAX_TABLE_SIZE;
71    }
72  }