C# 64 Bit Implementation of the Zobrist Hashing Algorithm.

Zobristhashing64.cs

public class ZOB64 : HashAlgorithm
    {
        private          ulong[]    _table;
        private          ulong      hash;
        private          uint       hash32;
        private readonly ulong      starthash = 0x391615744853B307;
        private          ZOB32State zhs;
        public ZOB64()
        {
            hash = starthash;
            BuildTable(0x7965CBDDD4A9E7AF);
        }
        public override int HashSize => 64;
        public override void Initialize()
        {
            hash = starthash;
        }
        protected override void HashCore(byte[] bytes, int ibStart, int cbSize)
        {
            Hash64(bytes, ibStart, cbSize);
        }
        private static ulong RotateLeft(ulong value, int count)
        {
            return (value << count) | (value >> (64 - count % 64));
        }
        private unsafe void Hash64(byte[] bytes, int ibStart, int cbSize)
        {
            if (bytes == null)
                return;
            if (ibStart >= bytes.Length || cbSize > bytes.Length)
                return;
            var i = 1;
            fixed (byte* pb = bytes)
            {
                var nb = pb + ibStart;
                while (cbSize >= 1)
                {
                    hash   ^= RotateLeft(_table[*nb], i++);
                    nb     += 1;
                    cbSize -= 1;
                }
            }
        }
        protected override byte[] HashFinal()
        {
            zhs.hash64 = hash;
            hash32     = zhs.hi ^ zhs.lo;
            return hash.GetBytes();
        }
        public void BuildTable(ulong seed)
        {
            var rnd = new CRng1(seed.GetBytes());
            var tt  = new CHashSet<ulong>(256);
            _table = new ulong[256];
            for (var i = 0; i < 256; i++)
            {
                ulong v;
                do
                {
                    v = rnd.NextULong();
                } while (tt.Contains(v));
                tt.Add(v);
                _table[i] = v;
            }
        }
        [StructLayout(LayoutKind.Explicit)]
        public struct ZOB32State
        {
            [FieldOffset(0)] public ulong hash64;
            [FieldOffset(0)] public uint  lo;
            [FieldOffset(4)] public uint  hi;
        }
    }