85 lines
2.1 KiB
C#
85 lines
2.1 KiB
C#
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using System;
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namespace TomShane.Neoforce.External.Zip
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{
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internal class CRC32
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{
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private UInt32[] crc32Table;
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private const int BUFFER_SIZE = 8192;
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private Int32 _TotalBytesRead= 0;
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public Int32 TotalBytesRead {
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get {
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return _TotalBytesRead;
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}
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}
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public UInt32 GetCrc32(System.IO.Stream input)
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{
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return GetCrc32AndCopy(input, null) ;
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}
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public UInt32 GetCrc32AndCopy(System.IO.Stream input, System.IO.Stream output)
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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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_TotalBytesRead= 0;
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int count = input.Read(buffer, 0, readSize);
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if (output != null) output.Write(buffer,0,count);
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_TotalBytesRead += count;
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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 = input.Read(buffer, 0, readSize);
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if (output != null) output.Write(buffer,0,count);
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_TotalBytesRead += count;
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}
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return ~crc32Result;
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}
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}
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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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