98 lines
3.2 KiB
C#
98 lines
3.2 KiB
C#
//
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// Copyright (c) 2008-2011, Kenneth Bell
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//
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// Permission is hereby granted, free of charge, to any person obtaining a
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// copy of this software and associated documentation files (the "Software"),
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// to deal in the Software without restriction, including without limitation
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// the rights to use, copy, modify, merge, publish, distribute, sublicense,
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// and/or sell copies of the Software, and to permit persons to whom the
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// Software is furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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// DEALINGS IN THE SOFTWARE.
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//
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namespace DiscUtils.Internal
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{
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/// <summary>
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/// Calculates CRC32 of buffers.
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/// </summary>
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internal sealed class Crc32LittleEndian : Crc32
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{
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private static readonly uint[][] Tables;
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static Crc32LittleEndian()
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{
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Tables = new uint[4][];
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Tables[(int)Crc32Algorithm.Common] = CalcTable(0xEDB88320);
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Tables[(int)Crc32Algorithm.Castagnoli] = CalcTable(0x82F63B78);
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Tables[(int)Crc32Algorithm.Koopman] = CalcTable(0xEB31D82E);
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Tables[(int)Crc32Algorithm.Aeronautical] = CalcTable(0xD5828281);
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}
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public Crc32LittleEndian(Crc32Algorithm algorithm)
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: base(Tables[(int)algorithm]) {}
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public static uint Compute(Crc32Algorithm algorithm, byte[] buffer, int offset, int count)
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{
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return Process(Tables[(int)algorithm], 0xFFFFFFFF, buffer, offset, count) ^ 0xFFFFFFFF;
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}
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public override void Process(byte[] buffer, int offset, int count)
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{
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_value = Process(Table, _value, buffer, offset, count);
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}
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private static uint[] CalcTable(uint polynomial)
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{
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uint[] table = new uint[256];
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table[0] = 0;
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for (uint i = 0; i <= 255; ++i)
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{
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uint crc = i;
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for (int j = 8; j > 0; --j)
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{
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if ((crc & 1) != 0)
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{
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crc = (crc >> 1) ^ polynomial;
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}
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else
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{
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crc >>= 1;
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}
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}
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table[i] = crc;
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}
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return table;
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}
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private static uint Process(uint[] table, uint accumulator, byte[] buffer, int offset, int count)
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{
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uint value = accumulator;
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for (int i = 0; i < count; ++i)
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{
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byte b = buffer[offset + i];
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uint temp1 = (value >> 8) & 0x00FFFFFF;
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uint temp2 = table[(value ^ b) & 0xFF];
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value = temp1 ^ temp2;
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}
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return value;
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}
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}
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} |