104 lines
3.1 KiB
C#
104 lines
3.1 KiB
C#
using System;
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using System.Text;
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using DotNetty.Buffers;
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namespace dotNetty_kcp
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{
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/// <summary>
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/// Computes a CRC32 checksum.
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/// </summary>
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/// <remarks>Based on <see cref="http://sanity-free.org/12/crc32_implementation_in_csharp.html"/></remarks>
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public static class Crc32
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{
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readonly static uint[] Table = CreateTable();
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static Crc32()
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{
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}
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// /// <summary>
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// /// Compute the checksum of a UTF8 text.
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// /// </summary>
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// /// <param name="text">Text to calculate</param>
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// /// <returns>Checksum</returns>
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// public static int ComputeChecksum(string text)
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// {
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// return ComputeChecksum(text, Encoding.UTF8);
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// }
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//
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// /// <summary>
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// /// Compute the checksum of a text using a specific encoding.
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// /// </summary>
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// /// <param name="text">Text to calculate</param>
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// /// <param name="encoding">Text encoding</param>
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// /// <returns>Checksum</returns>
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// public static int ComputeChecksum(string text, Encoding encoding)
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// {
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// if (string.IsNullOrEmpty(text)) return 0;
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// byte[] bytes = encoding.GetBytes(text);
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// return ComputeChecksum(bytes);
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// }
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/// <summary>
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/// Compute the checksum of a binary buffer.
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/// </summary>
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/// <param name="bytes">Buffer to calculate</param>
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/// <returns></returns>
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public static int ComputeChecksum(sbyte[] bytes)
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{
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uint crc = 0xffffffff;
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for (int i = 0; i < bytes.Length; i++)
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{
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byte index = (byte) (((crc) & 0xff) ^ bytes[i]);
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crc = (crc >> 8) ^ Table[index];
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}
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return unchecked((int) ~crc);
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}
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/// <summary>
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/// Compute the checksum of a binary buffer.
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/// </summary>
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/// <param name="bytes">Buffer to calculate</param>
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/// <returns></returns>
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public static uint ComputeChecksum(IByteBuffer byteBuffer,int offset,int lenth)
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{
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var crc = 0xffffffff;
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lenth += offset;
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for (var i = offset; i < lenth; i++)
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{
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var index = (byte) (((crc) & 0xff) ^ byteBuffer.GetByte(i));
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crc = (crc >> 8) ^ Table[index];
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}
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return ~crc;
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}
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static uint[] CreateTable()
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{
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const uint poly = 0xedb88320;
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var table = new uint[256];
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uint temp = 0;
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for (uint i = 0; i < table.Length; ++i)
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{
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temp = i;
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for (int j = 8; j > 0; --j)
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{
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if ((temp & 1) == 1)
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{
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temp = (uint) ((temp >> 1) ^ poly);
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}
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else
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{
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temp >>= 1;
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}
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}
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table[i] = temp;
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}
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return table;
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}
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}
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} |