1 /*
2  * Copyright (C) 2012 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 package com.google.common.hash;
16 
17 import static com.google.common.base.Preconditions.checkArgument;
18 import static com.google.common.base.Preconditions.checkNotNull;
19 
20 import com.google.common.base.Supplier;
21 
22 import java.io.Serializable;
23 import java.util.zip.Checksum;
24 
25 /**
26  * {@link HashFunction} adapter for {@link Checksum} instances.
27  *
28  * @author Colin Decker
29  */
30 final class ChecksumHashFunction extends AbstractStreamingHashFunction implements Serializable {
31 
32   private final Supplier<? extends Checksum> checksumSupplier;
33   private final int bits;
34   private final String toString;
35 
ChecksumHashFunction(Supplier<? extends Checksum> checksumSupplier, int bits, String toString)36   ChecksumHashFunction(Supplier<? extends Checksum> checksumSupplier, int bits, String toString) {
37     this.checksumSupplier = checkNotNull(checksumSupplier);
38     checkArgument(bits == 32 || bits == 64, "bits (%s) must be either 32 or 64", bits);
39     this.bits = bits;
40     this.toString = checkNotNull(toString);
41   }
42 
43   @Override
bits()44   public int bits() {
45     return bits;
46   }
47 
48   @Override
newHasher()49   public Hasher newHasher() {
50     return new ChecksumHasher(checksumSupplier.get());
51   }
52 
53   @Override
toString()54   public String toString() {
55     return toString;
56   }
57 
58   /**
59    * Hasher that updates a checksum.
60    */
61   private final class ChecksumHasher extends AbstractByteHasher {
62 
63     private final Checksum checksum;
64 
ChecksumHasher(Checksum checksum)65     private ChecksumHasher(Checksum checksum) {
66       this.checksum = checkNotNull(checksum);
67     }
68 
69     @Override
update(byte b)70     protected void update(byte b) {
71       checksum.update(b);
72     }
73 
74     @Override
update(byte[] bytes, int off, int len)75     protected void update(byte[] bytes, int off, int len) {
76       checksum.update(bytes, off, len);
77     }
78 
79     @Override
hash()80     public HashCode hash() {
81       long value = checksum.getValue();
82       if (bits == 32) {
83         /*
84          * The long returned from a 32-bit Checksum will have all 0s for its second word, so the
85          * cast won't lose any information and is necessary to return a HashCode of the correct
86          * size.
87          */
88         return HashCode.fromInt((int) value);
89       } else {
90         return HashCode.fromLong(value);
91       }
92     }
93   }
94 
95   private static final long serialVersionUID = 0L;
96 }
97