Crc32.cs

public static class Crc32
{
    private const uint Seed = 0xFFFFFFFF;

    private const uint Polynomial = 0xEDB88320;

    private static readonly uint[] LookupTable;

    static Crc32()
    {
        LookupTable = CreateLookupTable();
    }

    public static uint CalculateChecksum(string value)
    {
        return CalculateChecksum(Encoding.UTF8.GetBytes(value));
    }

    public static uint CalculateChecksum(byte[] buffer)
    {
	    return buffer.Aggregate(Seed, Lookup, value => value ^ Seed);
    }

    private static uint Lookup(uint value, byte b)
    {
        return (value >> 8) ^ LookupTable[(value & 0xFF) ^ b];
    }

    private static uint[] CreateLookupTable()
    {
        var table = new uint[256];

        for (var i = 0; i < 256; i++)
        {
            var entry = (uint) i;

            for (var j = 0; j < 8; j++)
            {
                entry = (entry & 1) == 1 ? (entry >> 1) ^ Polynomial : entry >> 1;
            }

            table[i] = entry;
        }

        return table;
    }
}