C# FNV1a 512Bit Implementation

FNV1a512.cs

public class FNV1a512 : HashAlgorithm
    {
        private readonly BigInteger _K = "35835915874844867368919076489095108449946327955754392558399825615420669938882575126094039892345713852759".NewBigInteger10();
        private BigInteger _hash;
        private readonly BigInteger Seed = "9659303129496669498009435400716310466090418745672637896108374329434462657994582932197716438449813051892206539805784495328239340083876191928701583869517785".NewBigInteger10();
        public FNV1a512()
        {
            _hash = Seed;
        }
        public FNV1a512(string seed)
        {
            Seed = seed.NewBigInteger10();
            _hash = Seed;
        }
        public override int HashSize => 512;
        public override void Initialize()
        {
            _hash = Seed;
        }
        protected override void HashCore(byte[] bytes, int ibStart, int cbSize)
        {
            Hash(bytes, ibStart, cbSize);
        }
        private void Hash(byte[] bytes, int ibStart, int cbSize)
        {
            if (bytes == null)
                return;
            if (ibStart >= bytes.Length || cbSize > bytes.Length)
                return;
            var p = 0;
            while (cbSize > 0)
            {
                _hash ^= bytes[p + ibStart];
                _hash *= _K;
                cbSize--;
                p++;
            }

            _hash = _hash ^ (_hash >> 256);
        }
        /// <summary>
        /// BigInteger does not overflow, so we limit the output to 512Bits.
        /// </summary>
        protected override byte[] HashFinal()
        {
            return _hash.ToByteArray().SubByte(0, 64);
        }
    }