75 lines
1.7 KiB
C#
75 lines
1.7 KiB
C#
using System;
|
|
using System.Collections.Generic;
|
|
using System.Text;
|
|
|
|
namespace WebsitePanel.FilesComparer
|
|
{
|
|
public class CRC32
|
|
{
|
|
private UInt32[] crc32Table;
|
|
private const int BUFFER_SIZE = 1024;
|
|
|
|
/// <summary>
|
|
/// Returns the CRC32 for the specified stream.
|
|
/// </summary>
|
|
/// <param name="stream">The stream to calculate the CRC32 for</param>
|
|
/// <returns>An unsigned integer containing the CRC32 calculation</returns>
|
|
public UInt32 GetCrc32(System.IO.Stream stream)
|
|
{
|
|
unchecked
|
|
{
|
|
UInt32 crc32Result;
|
|
crc32Result = 0xFFFFFFFF;
|
|
byte[] buffer = new byte[BUFFER_SIZE];
|
|
int readSize = BUFFER_SIZE;
|
|
|
|
int count = stream.Read(buffer, 0, readSize);
|
|
while (count > 0)
|
|
{
|
|
for (int i = 0; i < count; i++)
|
|
{
|
|
crc32Result = ((crc32Result) >> 8) ^ crc32Table[(buffer[i]) ^ ((crc32Result) & 0x000000FF)];
|
|
}
|
|
count = stream.Read(buffer, 0, readSize);
|
|
}
|
|
|
|
return ~crc32Result;
|
|
}
|
|
}
|
|
|
|
/// <summary>
|
|
/// Construct an instance of the CRC32 class, pre-initialising the table
|
|
/// for speed of lookup.
|
|
/// </summary>
|
|
public CRC32()
|
|
{
|
|
unchecked
|
|
{
|
|
// This is the official polynomial used by CRC32 in PKZip.
|
|
// Often the polynomial is shown reversed as 0x04C11DB7.
|
|
UInt32 dwPolynomial = 0xEDB88320;
|
|
UInt32 i, j;
|
|
|
|
crc32Table = new UInt32[256];
|
|
|
|
UInt32 dwCrc;
|
|
for (i = 0; i < 256; i++)
|
|
{
|
|
dwCrc = i;
|
|
for (j = 8; j > 0; j--)
|
|
{
|
|
if ((dwCrc & 1) == 1)
|
|
{
|
|
dwCrc = (dwCrc >> 1) ^ dwPolynomial;
|
|
}
|
|
else
|
|
{
|
|
dwCrc >>= 1;
|
|
}
|
|
}
|
|
crc32Table[i] = dwCrc;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|