aboutsummaryrefslogtreecommitdiffstatshomepage
path: root/OpenSim/Framework/Crc32.cs
diff options
context:
space:
mode:
Diffstat (limited to 'OpenSim/Framework/Crc32.cs')
-rw-r--r--OpenSim/Framework/Crc32.cs139
1 files changed, 139 insertions, 0 deletions
diff --git a/OpenSim/Framework/Crc32.cs b/OpenSim/Framework/Crc32.cs
new file mode 100644
index 0000000..7ad1566
--- /dev/null
+++ b/OpenSim/Framework/Crc32.cs
@@ -0,0 +1,139 @@
1/*
2 * Copyright (c) Contributors, http://opensimulator.org/
3 * See CONTRIBUTORS.TXT for a full list of copyright holders.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are met:
7 * * Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * * Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 * * Neither the name of the OpenSimulator Project nor the
13 * names of its contributors may be used to endorse or promote products
14 * derived from this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
17 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
18 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
19 * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
20 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
21 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
22 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
23 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
25 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 */
27
28using System;
29using System.Security.Cryptography;
30
31namespace OpenSim.Framework
32{
33 // this is more generic than openmetaverse CRC32
34
35 public class Crc32 : HashAlgorithm
36 {
37 public const UInt32 DefaultPolynomial = 0xedb88320;
38 public const UInt32 DefaultSeed = 0xffffffff;
39
40 private UInt32 hash;
41 private UInt32 seed;
42 private UInt32[] table;
43 private static UInt32[] defaultTable;
44
45 public Crc32()
46 {
47 table = InitializeTable(DefaultPolynomial);
48 seed = DefaultSeed;
49 Initialize();
50 }
51
52 public Crc32(UInt32 polynomial, UInt32 seed)
53 {
54 table = InitializeTable(polynomial);
55 this.seed = seed;
56 Initialize();
57 }
58
59 public override void Initialize()
60 {
61 hash = seed;
62 }
63
64 protected override void HashCore(byte[] buffer, int start, int length)
65 {
66 hash = CalculateHash(table, hash, buffer, start, length);
67 }
68
69 protected override byte[] HashFinal()
70 {
71 byte[] hashBuffer = UInt32ToBigEndianBytes(~hash);
72 this.HashValue = hashBuffer;
73 return hashBuffer;
74 }
75
76 public override int HashSize
77 {
78 get { return 32; }
79 }
80
81 public static UInt32 Compute(byte[] buffer)
82 {
83 return ~CalculateHash(InitializeTable(DefaultPolynomial), DefaultSeed, buffer, 0, buffer.Length);
84 }
85
86 public static UInt32 Compute(UInt32 seed, byte[] buffer)
87 {
88 return ~CalculateHash(InitializeTable(DefaultPolynomial), seed, buffer, 0, buffer.Length);
89 }
90
91 public static UInt32 Compute(UInt32 polynomial, UInt32 seed, byte[] buffer)
92 {
93 return ~CalculateHash(InitializeTable(polynomial), seed, buffer, 0, buffer.Length);
94 }
95
96 private static UInt32[] InitializeTable(UInt32 polynomial)
97 {
98 if (polynomial == DefaultPolynomial && defaultTable != null)
99 return defaultTable;
100
101 UInt32[] createTable = new UInt32[256];
102 for (int i = 0; i < 256; i++)
103 {
104 UInt32 entry = (UInt32)i;
105 for (int j = 0; j < 8; j++)
106 if ((entry & 1) == 1)
107 entry = (entry >> 1) ^ polynomial;
108 else
109 entry = entry >> 1;
110 createTable[i] = entry;
111 }
112
113 if (polynomial == DefaultPolynomial)
114 defaultTable = createTable;
115
116 return createTable;
117 }
118
119 private static UInt32 CalculateHash(UInt32[] table, UInt32 seed, byte[] buffer, int start, int size)
120 {
121 UInt32 crc = seed;
122 for (int i = start; i < size; i++)
123 unchecked
124 {
125 crc = (crc >> 8) ^ table[buffer[i] ^ crc & 0xff];
126 }
127 return crc;
128 }
129
130 private byte[] UInt32ToBigEndianBytes(UInt32 x)
131 {
132 return new byte[] {
133 (byte)((x >> 24) & 0xff),
134 (byte)((x >> 16) & 0xff),
135 (byte)((x >> 8) & 0xff),
136 (byte)(x & 0xff) };
137 }
138 }
139}