Coverage Summary for Class: Hashing (com.google.common.collect)

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 import org.checkerframework.checker.nullness.qual.Nullable;
22 
23 /**
24  * Static methods for implementing hash-based collections.
25  *
26  * @author Kevin Bourrillion
27  * @author Jesse Wilson
28  * @author Austin Appleby
29  */
30 @GwtCompatible
31 final class Hashing {
32   private Hashing() {}
33 
34   /*
35    * These should be ints, but we need to use longs to force GWT to do the multiplications with
36    * enough precision.
37    */
38   private static final long C1 = 0xcc9e2d51;
39   private static final long C2 = 0x1b873593;
40 
41   /*
42    * This method was rewritten in Java from an intermediate step of the Murmur hash function in
43    * http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp, which contained the
44    * following header:
45    *
46    * MurmurHash3 was written by Austin Appleby, and is placed in the public domain. The author
47    * hereby disclaims copyright to this source code.
48    */
49   static int smear(int hashCode) {
50     return (int) (C2 * Integer.rotateLeft((int) (hashCode * C1), 15));
51   }
52 
53   static int smearedHash(@Nullable Object o) {
54     return smear((o == null) ? 0 : o.hashCode());
55   }
56 
57   private static final int MAX_TABLE_SIZE = Ints.MAX_POWER_OF_TWO;
58 
59   static int closedTableSize(int expectedEntries, double loadFactor) {
60     // Get the recommended table size.
61     // Round down to the nearest power of 2.
62     expectedEntries = Math.max(expectedEntries, 2);
63     int tableSize = Integer.highestOneBit(expectedEntries);
64     // Check to make sure that we will not exceed the maximum load factor.
65     if (expectedEntries > (int) (loadFactor * tableSize)) {
66       tableSize <<= 1;
67       return (tableSize > 0) ? tableSize : MAX_TABLE_SIZE;
68     }
69     return tableSize;
70   }
71 
72   static boolean needsResizing(int size, int tableSize, double loadFactor) {
73     return size > loadFactor * tableSize && tableSize < MAX_TABLE_SIZE;
74   }
75 }