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Код

using System;
using System.IO;
using System.Text;
static class CRC32
{
    private static readonly uint[] crc_table = new uint[256];
    
    public const int BufferSize = 4096;
    
    static CRC32()
    {
        for (int n = 0; n < 256; ++n)
        {
            uint c = (uint) n;
            for (int k = 0; k < 8; ++k)
                if ((c & 1) != 0)
                    c = 0xEDB88320 ^ (c >> 1);
                else
                    c >>= 1;
            crc_table[n] = c;
        }
    }
    
    public static uint Update(uint crc, byte[] data, int offset, int count)
    {
        for (int n = offset; n < offset + count; ++n)
            crc = crc_table[(crc ^ data[n]) & 0xFF] ^ (crc >> 8);
        return crc;
    }
    
    public static uint Compute(byte[] data)
    {
        return Update(0xFFFFFFFF, data, 0, data.Length) ^ 0xFFFFFFFF;
    }
    
    public static uint Compute(Stream stream)
    {
        if (stream == null)
            throw new ArgumentNullException("stream");
        byte[] buffer = new byte[BufferSize];
        int readBytes = 0;
        uint crc = 0xFFFFFFFF;
        while ((readBytes = stream.Read(buffer, 0, BufferSize)) > 0)
        {
            crc = Update(crc, buffer, 0, readBytes);
        }
        return crc ^ 0xFFFFFFFF;
    }
}