103 lines
3.3 KiB
C#
103 lines
3.3 KiB
C#
// Copyright (c) 2014, Outercurve Foundation.
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// All rights reserved.
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//
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// Redistribution and use in source and binary forms, with or without modification,
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// are permitted provided that the following conditions are met:
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//
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// - Redistributions of source code must retain the above copyright notice, this
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// list of conditions and the following disclaimer.
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//
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// - Redistributions in binary form must reproduce the above copyright notice,
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// this list of conditions and the following disclaimer in the documentation
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// and/or other materials provided with the distribution.
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//
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// - Neither the name of the Outercurve Foundation nor the names of its
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// contributors may be used to endorse or promote products derived from this
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// software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
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// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
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// ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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// LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
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// ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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using System;
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using System.Collections.Generic;
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using System.Text;
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namespace WebsitePanel.FilesComparer
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{
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public class CRC32
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{
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private UInt32[] crc32Table;
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private const int BUFFER_SIZE = 1024;
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/// <summary>
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/// Returns the CRC32 for the specified stream.
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/// </summary>
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/// <param name="stream">The stream to calculate the CRC32 for</param>
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/// <returns>An unsigned integer containing the CRC32 calculation</returns>
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public UInt32 GetCrc32(System.IO.Stream stream)
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{
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unchecked
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{
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UInt32 crc32Result;
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crc32Result = 0xFFFFFFFF;
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byte[] buffer = new byte[BUFFER_SIZE];
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int readSize = BUFFER_SIZE;
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int count = stream.Read(buffer, 0, readSize);
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while (count > 0)
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{
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for (int i = 0; i < count; i++)
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{
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crc32Result = ((crc32Result) >> 8) ^ crc32Table[(buffer[i]) ^ ((crc32Result) & 0x000000FF)];
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}
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count = stream.Read(buffer, 0, readSize);
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}
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return ~crc32Result;
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}
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}
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/// <summary>
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/// Construct an instance of the CRC32 class, pre-initialising the table
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/// for speed of lookup.
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/// </summary>
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public CRC32()
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{
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unchecked
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{
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// This is the official polynomial used by CRC32 in PKZip.
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// Often the polynomial is shown reversed as 0x04C11DB7.
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UInt32 dwPolynomial = 0xEDB88320;
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UInt32 i, j;
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crc32Table = new UInt32[256];
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UInt32 dwCrc;
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for (i = 0; i < 256; i++)
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{
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dwCrc = i;
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for (j = 8; j > 0; j--)
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{
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if ((dwCrc & 1) == 1)
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{
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dwCrc = (dwCrc >> 1) ^ dwPolynomial;
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}
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else
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{
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dwCrc >>= 1;
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}
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}
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crc32Table[i] = dwCrc;
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}
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}
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}
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}
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}
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