public static class CRC16
{
    public static UInt16[] cp_Crc16_CCITT =
    {
        0x0000,0x1021, 0x2042,0x3063,0x4084,0x50A5,0x60C6,0x70E7,
        0x8108,0x9129,0xA14A,0xB16B,0xC18C,0xD1AD,0xE1CE,0xF1EF,
        0x1231,0x0210,0x3273,0x2252,0x52B5,0x4294,0x72F7,0x62D6,
        0x9339,0x8318,0xB37B,0xA35A,0xD3BD,0xC39C,0xF3FF,0xE3DE,
        0x2462,0x3443,0x0420,0x1401,0x64E6,0x74C7,0x44A4,0x5485,
        0xA56A,0xB54B,0x8528,0x9509,0xE5EE,0xF5CF,0xC5AC,0xD58D,
        0x3653,0x2672,0x1611,0x0630,0x76D7,0x66F6,0x5695,0x46B4,
        0xB75B,0xA77A,0x9719,0x8738,0xF7DF,0xE7FE,0xD79D,0xC7BC,
        0x48C4,0x58E5,0x6886,0x78A7,0x0840,0x1861,0x2802,0x3823,
        0xC9CC,0xD9ED,0xE98E,0xF9AF,0x8948,0x9969,0xA90A,0xB92B,
        0x5AF5,0x4AD4,0x7AB7,0x6A96,0x1A71,0x0A50,0x3A33,0x2A12,
        0xDBFD,0xCBDC,0xFBBF,0xEB9E,0x9B79,0x8B58,0xBB3B,0xAB1A,
        0x6CA6,0x7C87,0x4CE4,0x5CC5,0x2C22,0x3C03,0x0C60,0x1C41,
        0xEDAE,0xFD8F,0xCDEC,0xDDCD,0xAD2A,0xBD0B,0x8D68,0x9D49,
        0x7E97,0x6EB6,0x5ED5,0x4EF4,0x3E13,0x2E32,0x1E51,0x0E70,
        0xFF9F,0xEFBE,0xDFDD,0xCFFC,0xBF1B,0xAF3A,0x9F59,0x8F78,
        0x9188,0x81A9,0xB1CA,0xA1EB,0xD10C,0xC12D,0xF14E,0xE16F,
        0x1080,0x00A1,0x30C2,0x20E3,0x5004,0x4025,0x7046,0x6067,
        0x83B9,0x9398,0xA3FB,0xB3DA,0xC33D,0xD31C,0xE37F,0xF35E,
        0x02B1,0x1290,0x22F3,0x32D2,0x4235,0x5214,0x6277,0x7256,
        0xB5EA,0xA5CB,0x95A8,0x8589,0xF56E,0xE54F,0xD52C,0xC50D,
        0x34E2,0x24C3,0x14A0,0x0481,0x7466,0x6447,0x5424,0x4405,
        0xA7DB,0xB7FA,0x8799,0x97B8,0xE75F,0xF77E,0xC71D,0xD73C,
        0x26D3,0x36F2,0x0691,0x16B0,0x6657,0x7676,0x4615,0x5634,
        0xD94C,0xC96D,0xF90E,0xE92F,0x99C8,0x89E9,0xB98A,0xA9AB,
        0x5844,0x4865,0x7806,0x6827,0x18C0,0x08E1,0x3882,0x28A3,
        0xCB7D,0xDB5C,0xEB3F,0xFB1E,0x8BF9,0x9BD8,0xABBB,0xBB9A,
        0x4A75,0x5A54,0x6A37,0x7A16,0x0AF1,0x1AD0,0x2AB3,0x3A92,
        0xFD2E,0xED0F,0xDD6C,0xCD4D,0xBDAA,0xAD8B,0x9DE8,0x8DC9,
        0x7C26,0x6C07,0x5C64,0x4C45,0x3CA2,0x2C83,0x1CE0,0x0CC1,
        0xEF1F,0xFF3E,0xCF5D,0xDF7C,0xAF9B,0xBFBA,0x8FD9,0x9FF8,
        0x6E17,0x7E36,0x4E55,0x5E74,0x2E93,0x3EB2,0x0ED1,0x1EF0,
    };

    const ushort polynomial = 0xA001;
    static readonly ushort[] table = new ushort[256];

    static CRC16()
    {
        ushort value;
        ushort temp;
        for (ushort i = 0; i < table.Length; ++i)
        {
            value = 0;
            temp = i;
            for (byte j = 0; j < 8; ++j)
            {
                if (((value ^ temp) & 0x0001) != 0)
                {
                    value = (ushort)((value >> 1) ^ polynomial);
                }
                else
                {
                    value >>= 1;
                }
                temp >>= 1;
            }
            table[i] = value;
        }
    }

    public static ushort CalcRedisSlot(string key)
    {
        return Convert.ToUInt16(CRC16CCITT2(Encoding.ASCII.GetBytes(key), 0) & 16383);
    }

    public static ushort CRC16CCITT2(byte[] bytes, ushort initialValue)
    {
        const ushort poly = 0x1021;
        ushort[] table = new ushort[256];
        ushort temp, a;
        ushort crc = initialValue;
        for (int i = 0; i < table.Length; ++i)
        {
            temp = 0;
            a = (ushort)(i << 8);
            for (int j = 0; j < 8; ++j)
            {
                if (((temp ^ a) & 0x8000) != 0)
                    temp = (ushort)((temp << 1) ^ poly);
                else
                    temp <<= 1;
                a <<= 1;
            }
            table[i] = temp;
        }
        for (int i = 0; i < bytes.Length; ++i)
        {
            crc = (ushort)((crc << 8) ^ table[((crc >> 8) ^ (0xff & bytes[i]))]);
        }
        return crc;
    }
}

int slot = CRC16.CalcRedisSlot("123456789");
Console.WriteLine(Convert.ToString(slot, 16));

https://github.com/redis/redis/blob/unstable/src/crc16.c
https://www.devcoons.com/c-crc16-algorithm/
https://redis.io/docs/reference/cluster-spec/
https://redis.com/blog/redis-clustering-best-practices-with-keys/