CRC32.cs

public class CRC32
{
    private const int TABLE_LENGTH = 256;
    private uint[] crcTable;

    public CRC32()
    {
        BuildCRC32Table();
    }
    
    private void BuildCRC32Table()
    {
        crcTable = new uint[256];
        for (uint i = 0; i < 256; i++)
        {
            var x = i;
            for (var j = 0; j < 8; j++)
            {
                x = (uint)((x & 1) == 0 ? x >> 1 : -306674912 ^ x >> 1);
            }
            crcTable[i] = x;
        }
    }

    public uint Calc(byte[] buf)
    {
        uint num = uint.MaxValue;
        for (var i = 0; i < buf.Length; i++)
        {
            num = crcTable[(num ^ buf[i]) & 255] ^ num >> 8;
        }

        return (uint)(num ^ -1);
    }
}