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| 1 | +// Adler32.cs - Computes Adler32 data checksum of a data stream |
| 2 | +// Copyright (C) 2001 Mike Krueger |
| 3 | +// |
| 4 | +// This file was translated from java, it was part of the GNU Classpath |
| 5 | +// Copyright (C) 1999, 2000, 2001 Free Software Foundation, Inc. |
| 6 | +// |
| 7 | +// This program is free software; you can redistribute it and/or |
| 8 | +// modify it under the terms of the GNU General Public License |
| 9 | +// as published by the Free Software Foundation; either version 2 |
| 10 | +// of the License, or (at your option) any later version. |
| 11 | +// |
| 12 | +// This program is distributed in the hope that it will be useful, |
| 13 | +// but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 15 | +// GNU General Public License for more details. |
| 16 | +// |
| 17 | +// You should have received a copy of the GNU General Public License |
| 18 | +// along with this program; if not, write to the Free Software |
| 19 | +// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. |
| 20 | +// |
| 21 | +// Linking this library statically or dynamically with other modules is |
| 22 | +// making a combined work based on this library. Thus, the terms and |
| 23 | +// conditions of the GNU General Public License cover the whole |
| 24 | +// combination. |
| 25 | +// |
| 26 | +// As a special exception, the copyright holders of this library give you |
| 27 | +// permission to link this library with independent modules to produce an |
| 28 | +// executable, regardless of the license terms of these independent |
| 29 | +// modules, and to copy and distribute the resulting executable under |
| 30 | +// terms of your choice, provided that you also meet, for each linked |
| 31 | +// independent module, the terms and conditions of the license of that |
| 32 | +// module. An independent module is a module which is not derived from |
| 33 | +// or based on this library. If you modify this library, you may extend |
| 34 | +// this exception to your version of the library, but you are not |
| 35 | +// obligated to do so. If you do not wish to do so, delete this |
| 36 | +// exception statement from your version. |
| 37 | + |
| 38 | +using System; |
| 39 | + |
| 40 | +namespace GitHub.ICSharpCode.SharpZipLib.Checksums |
| 41 | +{ |
| 42 | + |
| 43 | + /// <summary> |
| 44 | + /// Computes Adler32 checksum for a stream of data. An Adler32 |
| 45 | + /// checksum is not as reliable as a CRC32 checksum, but a lot faster to |
| 46 | + /// compute. |
| 47 | + /// |
| 48 | + /// The specification for Adler32 may be found in RFC 1950. |
| 49 | + /// ZLIB Compressed Data Format Specification version 3.3) |
| 50 | + /// |
| 51 | + /// |
| 52 | + /// From that document: |
| 53 | + /// |
| 54 | + /// "ADLER32 (Adler-32 checksum) |
| 55 | + /// This contains a checksum value of the uncompressed data |
| 56 | + /// (excluding any dictionary data) computed according to Adler-32 |
| 57 | + /// algorithm. This algorithm is a 32-bit extension and improvement |
| 58 | + /// of the Fletcher algorithm, used in the ITU-T X.224 / ISO 8073 |
| 59 | + /// standard. |
| 60 | + /// |
| 61 | + /// Adler-32 is composed of two sums accumulated per byte: s1 is |
| 62 | + /// the sum of all bytes, s2 is the sum of all s1 values. Both sums |
| 63 | + /// are done modulo 65521. s1 is initialized to 1, s2 to zero. The |
| 64 | + /// Adler-32 checksum is stored as s2*65536 + s1 in most- |
| 65 | + /// significant-byte first (network) order." |
| 66 | + /// |
| 67 | + /// "8.2. The Adler-32 algorithm |
| 68 | + /// |
| 69 | + /// The Adler-32 algorithm is much faster than the CRC32 algorithm yet |
| 70 | + /// still provides an extremely low probability of undetected errors. |
| 71 | + /// |
| 72 | + /// The modulo on unsigned long accumulators can be delayed for 5552 |
| 73 | + /// bytes, so the modulo operation time is negligible. If the bytes |
| 74 | + /// are a, b, c, the second sum is 3a + 2b + c + 3, and so is position |
| 75 | + /// and order sensitive, unlike the first sum, which is just a |
| 76 | + /// checksum. That 65521 is prime is important to avoid a possible |
| 77 | + /// large class of two-byte errors that leave the check unchanged. |
| 78 | + /// (The Fletcher checksum uses 255, which is not prime and which also |
| 79 | + /// makes the Fletcher check insensitive to single byte changes 0 - |
| 80 | + /// 255.) |
| 81 | + /// |
| 82 | + /// The sum s1 is initialized to 1 instead of zero to make the length |
| 83 | + /// of the sequence part of s2, so that the length does not have to be |
| 84 | + /// checked separately. (Any sequence of zeroes has a Fletcher |
| 85 | + /// checksum of zero.)" |
| 86 | + /// </summary> |
| 87 | + /// <see cref="ICSharpCode.SharpZipLib.Zip.Compression.Streams.InflaterInputStream"/> |
| 88 | + /// <see cref="ICSharpCode.SharpZipLib.Zip.Compression.Streams.DeflaterOutputStream"/> |
| 89 | + public sealed class Adler32 : IChecksum |
| 90 | + { |
| 91 | + /// <summary> |
| 92 | + /// largest prime smaller than 65536 |
| 93 | + /// </summary> |
| 94 | + const uint BASE = 65521; |
| 95 | + |
| 96 | + /// <summary> |
| 97 | + /// Returns the Adler32 data checksum computed so far. |
| 98 | + /// </summary> |
| 99 | + public long Value { |
| 100 | + get { |
| 101 | + return checksum; |
| 102 | + } |
| 103 | + } |
| 104 | + |
| 105 | + /// <summary> |
| 106 | + /// Creates a new instance of the Adler32 class. |
| 107 | + /// The checksum starts off with a value of 1. |
| 108 | + /// </summary> |
| 109 | + public Adler32() |
| 110 | + { |
| 111 | + Reset(); |
| 112 | + } |
| 113 | + |
| 114 | + /// <summary> |
| 115 | + /// Resets the Adler32 checksum to the initial value. |
| 116 | + /// </summary> |
| 117 | + public void Reset() |
| 118 | + { |
| 119 | + checksum = 1; |
| 120 | + } |
| 121 | + |
| 122 | + /// <summary> |
| 123 | + /// Updates the checksum with a byte value. |
| 124 | + /// </summary> |
| 125 | + /// <param name="value"> |
| 126 | + /// The data value to add. The high byte of the int is ignored. |
| 127 | + /// </param> |
| 128 | + public void Update(int value) |
| 129 | + { |
| 130 | + // We could make a length 1 byte array and call update again, but I |
| 131 | + // would rather not have that overhead |
| 132 | + uint s1 = checksum & 0xFFFF; |
| 133 | + uint s2 = checksum >> 16; |
| 134 | + |
| 135 | + s1 = (s1 + ((uint)value & 0xFF)) % BASE; |
| 136 | + s2 = (s1 + s2) % BASE; |
| 137 | + |
| 138 | + checksum = (s2 << 16) + s1; |
| 139 | + } |
| 140 | + |
| 141 | + /// <summary> |
| 142 | + /// Updates the checksum with an array of bytes. |
| 143 | + /// </summary> |
| 144 | + /// <param name="buffer"> |
| 145 | + /// The source of the data to update with. |
| 146 | + /// </param> |
| 147 | + public void Update(byte[] buffer) |
| 148 | + { |
| 149 | + if ( buffer == null ) { |
| 150 | + throw new ArgumentNullException("buffer"); |
| 151 | + } |
| 152 | + |
| 153 | + Update(buffer, 0, buffer.Length); |
| 154 | + } |
| 155 | + |
| 156 | + /// <summary> |
| 157 | + /// Updates the checksum with the bytes taken from the array. |
| 158 | + /// </summary> |
| 159 | + /// <param name="buffer"> |
| 160 | + /// an array of bytes |
| 161 | + /// </param> |
| 162 | + /// <param name="offset"> |
| 163 | + /// the start of the data used for this update |
| 164 | + /// </param> |
| 165 | + /// <param name="count"> |
| 166 | + /// the number of bytes to use for this update |
| 167 | + /// </param> |
| 168 | + public void Update(byte[] buffer, int offset, int count) |
| 169 | + { |
| 170 | + if (buffer == null) { |
| 171 | + throw new ArgumentNullException("buffer"); |
| 172 | + } |
| 173 | + |
| 174 | + if (offset < 0) { |
| 175 | +#if NETCF_1_0 |
| 176 | + throw new ArgumentOutOfRangeException("offset"); |
| 177 | +#else |
| 178 | + throw new ArgumentOutOfRangeException("offset", "cannot be negative"); |
| 179 | +#endif |
| 180 | + } |
| 181 | + |
| 182 | + if ( count < 0 ) |
| 183 | + { |
| 184 | +#if NETCF_1_0 |
| 185 | + throw new ArgumentOutOfRangeException("count"); |
| 186 | +#else |
| 187 | + throw new ArgumentOutOfRangeException("count", "cannot be negative"); |
| 188 | +#endif |
| 189 | + } |
| 190 | + |
| 191 | + if (offset >= buffer.Length) |
| 192 | + { |
| 193 | +#if NETCF_1_0 |
| 194 | + throw new ArgumentOutOfRangeException("offset"); |
| 195 | +#else |
| 196 | + throw new ArgumentOutOfRangeException("offset", "not a valid index into buffer"); |
| 197 | +#endif |
| 198 | + } |
| 199 | + |
| 200 | + if (offset + count > buffer.Length) |
| 201 | + { |
| 202 | +#if NETCF_1_0 |
| 203 | + throw new ArgumentOutOfRangeException("count"); |
| 204 | +#else |
| 205 | + throw new ArgumentOutOfRangeException("count", "exceeds buffer size"); |
| 206 | +#endif |
| 207 | + } |
| 208 | + |
| 209 | + //(By Per Bothner) |
| 210 | + uint s1 = checksum & 0xFFFF; |
| 211 | + uint s2 = checksum >> 16; |
| 212 | + |
| 213 | + while (count > 0) { |
| 214 | + // We can defer the modulo operation: |
| 215 | + // s1 maximally grows from 65521 to 65521 + 255 * 3800 |
| 216 | + // s2 maximally grows by 3800 * median(s1) = 2090079800 < 2^31 |
| 217 | + int n = 3800; |
| 218 | + if (n > count) { |
| 219 | + n = count; |
| 220 | + } |
| 221 | + count -= n; |
| 222 | + while (--n >= 0) { |
| 223 | + s1 = s1 + (uint)(buffer[offset++] & 0xff); |
| 224 | + s2 = s2 + s1; |
| 225 | + } |
| 226 | + s1 %= BASE; |
| 227 | + s2 %= BASE; |
| 228 | + } |
| 229 | + |
| 230 | + checksum = (s2 << 16) | s1; |
| 231 | + } |
| 232 | + |
| 233 | + #region Instance Fields |
| 234 | + uint checksum; |
| 235 | + #endregion |
| 236 | + } |
| 237 | +} |
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