mirror of
https://github.com/ShareX/ShareX.git
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152 lines
No EOL
4.4 KiB
C#
152 lines
No EOL
4.4 KiB
C#
#region License Information (GPL v3)
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/*
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ShareX - A program that allows you to take screenshots and share any file type
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Copyright © 2007-2015 ShareX Developers
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License
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as published by the Free Software Foundation; either version 2
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of the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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Optionally you can also view the license at <http://www.gnu.org/licenses/>.
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*/
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#endregion License Information (GPL v3)
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using System.Security.Cryptography;
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namespace ShareX.HelpersLib
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{
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// http://damieng.com/blog/2006/08/08/calculating_crc32_in_c_and_net
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public class Crc32 : HashAlgorithm
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{
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public const uint DefaultPolynomial = 0xedb88320;
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public const uint DefaultSeed = 0xffffffff;
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private uint hash;
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private uint seed;
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private uint[] table;
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private static uint[] defaultTable;
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public Crc32()
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{
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table = InitializeTable(DefaultPolynomial);
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seed = DefaultSeed;
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Initialize();
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}
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public Crc32(uint polynomial, uint seed)
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{
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table = InitializeTable(polynomial);
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this.seed = seed;
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Initialize();
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}
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public override void Initialize()
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{
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hash = seed;
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}
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protected override void HashCore(byte[] buffer, int start, int length)
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{
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hash = CalculateHash(table, hash, buffer, start, length);
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}
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protected override byte[] HashFinal()
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{
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byte[] hashBuffer = uintToBigEndianBytes(~hash);
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HashValue = hashBuffer;
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return hashBuffer;
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}
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public override int HashSize
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{
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get
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{
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return 32;
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}
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}
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public static uint Compute(byte[] buffer)
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{
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return ~CalculateHash(InitializeTable(DefaultPolynomial), DefaultSeed, buffer, 0, buffer.Length);
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}
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public static uint Compute(uint seed, byte[] buffer)
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{
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return ~CalculateHash(InitializeTable(DefaultPolynomial), seed, buffer, 0, buffer.Length);
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}
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public static uint Compute(uint polynomial, uint seed, byte[] buffer)
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{
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return ~CalculateHash(InitializeTable(polynomial), seed, buffer, 0, buffer.Length);
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}
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private static uint[] InitializeTable(uint polynomial)
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{
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if (polynomial == DefaultPolynomial && defaultTable != null)
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{
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return defaultTable;
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}
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uint[] createTable = new uint[256];
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for (int i = 0; i < 256; i++)
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{
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uint entry = (uint)i;
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for (int j = 0; j < 8; j++)
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{
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if ((entry & 1) == 1)
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{
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entry = (entry >> 1) ^ polynomial;
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}
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else
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{
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entry = entry >> 1;
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}
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}
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createTable[i] = entry;
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}
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if (polynomial == DefaultPolynomial)
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{
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defaultTable = createTable;
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}
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return createTable;
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}
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private static uint CalculateHash(uint[] table, uint seed, byte[] buffer, int start, int size)
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{
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uint crc = seed;
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for (int i = start; i < size; i++)
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{
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unchecked
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{
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crc = (crc >> 8) ^ table[buffer[i] ^ crc & 0xff];
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}
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}
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return crc;
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}
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private byte[] uintToBigEndianBytes(uint x)
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{
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return new byte[]
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{
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(byte)((x >> 24) & 0xff),
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(byte)((x >> 16) & 0xff),
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(byte)((x >> 8) & 0xff),
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(byte)(x & 0xff)
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};
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}
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}
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} |