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
17/**
18 * Static factories for {@link HashCode} instances.
19 *
20 * @author andreou@google.com (Dimitris Andreou)
21 */
22final class HashCodes {
23  private HashCodes() { }
24
25  /**
26   * Creates a 32-bit {@code HashCode}, of which the bytes will form the passed int, interpreted
27   * in little endian order.
28   */
29  static HashCode fromInt(int hash) {
30    return new IntHashCode(hash);
31  }
32
33  private static class IntHashCode extends HashCode {
34    final int hash;
35
36    IntHashCode(int hash) {
37      this.hash = hash;
38    }
39
40    @Override public int bits() {
41      return 32;
42    }
43
44    @Override public byte[] asBytes() {
45      return new byte[] {
46          (byte) hash,
47          (byte) (hash >> 8),
48          (byte) (hash >> 16),
49          (byte) (hash >> 24)};
50    }
51
52    @Override public int asInt() {
53      return hash;
54    }
55
56    @Override public long asLong() {
57      throw new IllegalStateException("this HashCode only has 32 bits; cannot create a long");
58    }
59  }
60
61  /**
62   * Creates a 64-bit {@code HashCode}, of which the bytes will form the passed long, interpreted
63   * in little endian order.
64   */
65  static HashCode fromLong(long hash) {
66    return new LongHashCode(hash);
67  }
68
69  private static class LongHashCode extends HashCode {
70    final long hash;
71
72    LongHashCode(long hash) {
73      this.hash = hash;
74    }
75
76    @Override public int bits() {
77      return 64;
78    }
79
80    @Override public byte[] asBytes() {
81      return new byte[] {
82          (byte) hash,
83          (byte) (hash >> 8),
84          (byte) (hash >> 16),
85          (byte) (hash >> 24),
86          (byte) (hash >> 32),
87          (byte) (hash >> 40),
88          (byte) (hash >> 48),
89          (byte) (hash >> 56)};
90    }
91
92    @Override public int asInt() {
93      return (int) hash;
94    }
95
96    @Override public long asLong() {
97      return hash;
98    }
99  }
100
101  /**
102   * Creates a {@code HashCode} from a byte array. The array is <i>not</i> copied defensively,
103   * so it must be handed-off so as to preserve the immutability contract of {@code HashCode}.
104   * The array must be at least of length 4 (not checked).
105   */
106  static HashCode fromBytes(byte[] bytes) {
107    return new BytesHashCode(bytes);
108  }
109
110  private static class BytesHashCode extends HashCode {
111    final byte[] bytes;
112
113    BytesHashCode(byte[] bytes) {
114      this.bytes = bytes;
115    }
116
117    @Override public int bits() {
118      return bytes.length * 8;
119    }
120
121    @Override public byte[] asBytes() {
122      return bytes.clone();
123    }
124
125    @Override public int asInt() {
126      return (bytes[0] & 0xFF)
127          | ((bytes[1] & 0xFF) << 8)
128          | ((bytes[2] & 0xFF) << 16)
129          | ((bytes[3] & 0xFF) << 24);
130    }
131
132    @Override public long asLong() {
133      if (bytes.length < 8) {
134        // Checking this to throw the correct type of exception
135        throw new IllegalStateException("Not enough bytes");
136      }
137      return (bytes[0] & 0xFFL)
138          | ((bytes[1] & 0xFFL) << 8)
139          | ((bytes[2] & 0xFFL) << 16)
140          | ((bytes[3] & 0xFFL) << 24)
141          | ((bytes[4] & 0xFFL) << 32)
142          | ((bytes[5] & 0xFFL) << 40)
143          | ((bytes[6] & 0xFFL) << 48)
144          | ((bytes[7] & 0xFFL) << 56);
145    }
146  }
147}
148