HexToByteArray

    public unsafe static class FastConverter
    {
        static readonly byte[] HiTable =
        {
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 0, 16,
            32, 48, 64, 80, 96, 112, 128, 144, 255, 255,
            255, 255, 255, 255, 255, 160, 176, 192, 208, 224,
            240, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 160, 176, 192,
            208, 224, 240
        };

        static readonly byte[] LoTable =
        {
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 0, 1,
            2, 3, 4, 5, 6, 7, 8, 9, 255, 255,
            255, 255, 255, 255, 255, 10, 11, 12, 13, 14,
            15, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
            255, 255, 255, 255, 255, 255, 255, 10, 11, 12,
            13, 14, 15
        };

        public static byte[] FromHexString(string source)
        {
            // No checks, quality (not null and even chars) of source garanteed

            var result = new byte[source.Length >> 1];

            fixed (char* sourceRef = source)
            fixed (byte* resultRef = result)
            {
                fixed (byte* hiRef = HiTable)
                fixed (byte* lowRef = LoTable)
                {
                    char* s = &sourceRef[0];
                    byte* r = resultRef;
                    while (*s != 0)
                    {
                        *r = hiRef[*s++];
                        *r++ += lowRef[*s++];
                    }
                    return result;
                }
            }
        }
    }