/**
* Digital Voice Modem - Fixed Network Equipment
* AGPLv3 Open Source. Use is subject to license terms.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* @package DVM / Fixed Network Equipment
*
*/
//
// Based on code from the MMDVMHost project. (https://github.com/g4klx/MMDVMHost)
// Licensed under the GPLv2 License (https://opensource.org/licenses/GPL-2.0)
//
/*
*   Copyright (C) 2016 by Jonathan Naylor G4KLX
*   Copyright (C) 2017-2023 by Bryan Biedenkapp N2PLL
*
*   This program is free software; you can redistribute it and/or modify
*   it under the terms of the GNU General Public License as published by
*   the Free Software Foundation; either version 2 of the License, or
*   (at your option) any later version.
*
*   This program is distributed in the hope that it will be useful,
*   but WITHOUT ANY WARRANTY; without even the implied warranty of
*   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*   GNU General Public License for more details.
*
*   You should have received a copy of the GNU General Public License
*   along with this program; if not, write to the Free Software
*   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

using System;

namespace fnecore.EDAC.RS
{
    /// <summary>
    /// Implements Reed-Solomon encoding, as the name implies.
    /// </summary>
    internal sealed class ReedSolomonEncoder
    {
        private static readonly byte[][] ENCODE_MATRIX = new byte[12][] {
            new byte[24] { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 062, 044, 003, 025, 014, 016, 027, 003, 053, 004, 036, 047 },
            new byte[24] { 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 011, 012, 011, 011, 016, 064, 067, 055, 001, 076, 026, 073 },
            new byte[24] { 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 003, 001, 005, 075, 014, 006, 020, 044, 066, 006, 070, 066 },
            new byte[24] { 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 021, 070, 027, 045, 016, 067, 023, 064, 073, 033, 044, 021 },
            new byte[24] { 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 030, 022, 003, 075, 015, 015, 033, 015, 051, 003, 053, 050 },
            new byte[24] { 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 001, 041, 027, 056, 076, 064, 021, 053, 004, 025, 001, 012 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 061, 076, 021, 055, 076, 001, 063, 035, 030, 013, 064, 070 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 024, 022, 071, 056, 021, 035, 073, 042, 057, 074, 043, 076 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 072, 042, 005, 020, 043, 047, 033, 056, 001, 016, 013, 076 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 072, 014, 065, 054, 035, 025, 041, 016, 015, 040, 071, 026 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 073, 065, 036, 061, 042, 022, 017, 004, 044, 020, 025, 005 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 071, 005, 055, 003, 071, 034, 060, 011, 074, 002, 041, 050 } 
        };

        private static readonly byte[][] ENCODE_MATRIX_24169 = new byte[16][] {
            new byte[24] { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 051, 045, 067, 015, 064, 067, 052, 012 },
            new byte[24] { 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 057, 025, 063, 073, 071, 022, 040, 015 },
            new byte[24] { 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 005, 001, 031, 004, 016, 054, 025, 076 },
            new byte[24] { 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 073, 007, 047, 014, 041, 077, 047, 011 },
            new byte[24] { 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 075, 015, 051, 051, 017, 067, 017, 057 },
            new byte[24] { 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 020, 032, 014, 042, 075, 042, 070, 054 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 002, 075, 043, 005, 001, 040, 012, 064 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 024, 074, 015, 072, 024, 026, 074, 061 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 042, 064, 007, 022, 061, 020, 040, 065 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 032, 032, 055, 041, 057, 066, 021, 077 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 065, 036, 025, 007, 050, 016, 040, 051 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 064, 006, 054, 032, 076, 046, 014, 036 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 062, 063, 074, 070, 005, 027, 037, 046 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 055, 043, 034, 071, 057, 076, 050, 064 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 024, 023, 023, 005, 050, 070, 042, 023 },
            new byte[24] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 067, 075, 045, 060, 057, 024, 006, 026 } 
        };

        private static readonly byte[][] ENCODE_MATRIX_362017 = new byte[20][] {
            new byte[36] { 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 074, 037, 034, 006, 002, 007, 044, 064, 026, 014, 026, 044, 054, 013, 077, 005 },
            new byte[36] { 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 004, 017, 050, 024, 011, 005, 030, 057, 033, 003, 002, 002, 015, 016, 025, 026 },
            new byte[36] { 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 007, 023, 037, 046, 056, 075, 043, 045, 055, 021, 050, 031, 045, 027, 071, 062 },
            new byte[36] { 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 026, 005, 007, 063, 063, 027, 063, 040, 006, 004, 040, 045, 047, 030, 075, 007 },
            new byte[36] { 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 023, 073, 073, 041, 072, 034, 021, 051, 067, 016, 031, 074, 011, 021, 012, 021 },
            new byte[36] { 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 024, 051, 025, 023, 022, 041, 074, 066, 074, 065, 070, 036, 067, 045, 064, 001 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 052, 033, 014, 002, 020, 006, 014, 025, 052, 023, 035, 074, 075, 075, 043, 027 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 055, 062, 056, 025, 073, 060, 015, 030, 013, 017, 020, 002, 070, 055, 014, 047 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 054, 051, 032, 065, 077, 012, 054, 013, 035, 032, 056, 012, 075, 001, 072, 063 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 074, 041, 030, 041, 043, 022, 051, 006, 064, 033, 003, 047, 027, 012, 055, 047 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 054, 070, 011, 003, 013, 022, 016, 057, 003, 045, 072, 031, 030, 056, 035, 022 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 051, 007, 072, 030, 065, 054, 006, 021, 036, 063, 050, 061, 064, 052, 001, 060 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 001, 065, 032, 070, 013, 044, 073, 024, 012, 052, 021, 055, 012, 035, 014, 072 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 011, 070, 005, 010, 065, 024, 015, 077, 022, 024, 024, 074, 007, 044, 007, 046 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 006, 002, 065, 011, 041, 020, 045, 042, 046, 054, 035, 012, 040, 064, 065, 033 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 034, 031, 001, 015, 044, 064, 016, 024, 052, 016, 006, 062, 020, 013, 055, 057 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 063, 043, 025, 044, 077, 063, 017, 017, 064, 014, 040, 074, 031, 072, 054, 006 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 071, 021, 070, 044, 056, 004, 030, 074, 004, 023, 071, 070, 063, 045, 056, 043 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 002, 001, 053, 074, 002, 014, 052, 074, 012, 057, 024, 063, 015, 042, 052, 033 },
            new byte[36] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 034, 035, 002, 023, 021, 027, 022, 033, 064, 042, 005, 073, 051, 046, 073, 060 } 
        };

        /*
        ** Methods
        */

        /// <summary>
        /// Encode RS (24,12,13) FEC.
        /// </summary>
        /// <param name="data">Raw data to encode with Reed-Solomon FEC.</param>
        public void encode241213(ref byte[] data)
        {
            if (data == null)
                throw new NullReferenceException();

            byte[] codeword = new byte[24U];

            for (uint i = 0U; i < 24U; i++)
            {
                codeword[i] = 0x00;

                uint offs = 0U;
                for (uint j = 0U; j < 12U; j++, offs += 6U)
                {
                    byte hexbit = bin2Hex(data, offs);
                    codeword[i] ^= gf6Mult(hexbit, ENCODE_MATRIX[j][i]);
                }
            }

            uint offset = 0U;
            for (uint i = 0U; i < 24U; i++, offset += 6U)
                hex2Bin(codeword[i], ref data, offset);
        }

        /// <summary>
        /// Encode RS (24,16,9) FEC.
        /// </summary>
        /// <param name="data">Raw data to encode with Reed-Solomon FEC.</param>
        public void encode24169(ref byte[] data)
        {
            if (data == null)
                throw new NullReferenceException();

            byte[] codeword = new byte[24U];

            for (uint i = 0U; i < 24U; i++)
            {
                codeword[i] = 0x00;

                uint offs = 0U;
                for (uint j = 0U; j < 16U; j++, offs += 6U)
                {
                    byte hexbit = bin2Hex(data, offs);
                    codeword[i] ^= gf6Mult(hexbit, ENCODE_MATRIX_24169[j][i]);
                }
            }

            uint offset = 0U;
            for (uint i = 0U; i < 24U; i++, offset += 6U)
                hex2Bin(codeword[i], ref data, offset);
        }

        /// <summary>
        /// Encode RS (36,20,17) FEC.
        /// </summary>
        /// <param name="data">Raw data to encode with Reed-Solomon FEC.</param>
        public void encode362017(ref byte[] data)
        {
            if (data == null)
                throw new NullReferenceException();

            byte[] codeword = new byte[36U];

            for (uint i = 0U; i < 36U; i++)
            {
                codeword[i] = 0x00;

                uint offs = 0U;
                for (uint j = 0U; j < 20U; j++, offs += 6U)
                {
                    byte hexbit = bin2Hex(data, offs);
                    codeword[i] ^= gf6Mult(hexbit, ENCODE_MATRIX_362017[j][i]);
                }
            }

            uint offset = 0U;
            for (uint i = 0U; i < 36U; i++, offset += 6U)
                hex2Bin(codeword[i], ref data, offset);
        }

        /// <summary>
        ///
        /// </summary>
        /// <param name="input"></param>
        /// <param name="offset"></param>
        /// <returns></returns>
        private byte bin2Hex(byte[] input, uint offset)
        {
            byte output = 0x00;

            output |= (byte)(FneUtils.ReadBit(input, offset + 0U) ? 0x20U : 0x00U);
            output |= (byte)(FneUtils.ReadBit(input, offset + 1U) ? 0x10U : 0x00U);
            output |= (byte)(FneUtils.ReadBit(input, offset + 2U) ? 0x08U : 0x00U);
            output |= (byte)(FneUtils.ReadBit(input, offset + 3U) ? 0x04U : 0x00U);
            output |= (byte)(FneUtils.ReadBit(input, offset + 4U) ? 0x02U : 0x00U);
            output |= (byte)(FneUtils.ReadBit(input, offset + 5U) ? 0x01U : 0x00U);

            return output;
        }

        /// <summary>
        ///
        /// </summary>
        /// <param name="input"></param>
        /// <param name="output"></param>
        /// <param name="offset"></param>
        /// <returns></returns>
        private void hex2Bin(byte input, ref byte[] output, uint offset)
        {
            FneUtils.WriteBit(ref output, offset + 0U, (input & 0x20U) == 0x20U);
            FneUtils.WriteBit(ref output, offset + 1U, (input & 0x10U) == 0x10U);
            FneUtils.WriteBit(ref output, offset + 2U, (input & 0x08U) == 0x08U);
            FneUtils.WriteBit(ref output, offset + 3U, (input & 0x04U) == 0x04U);
            FneUtils.WriteBit(ref output, offset + 4U, (input & 0x02U) == 0x02U);
            FneUtils.WriteBit(ref output, offset + 5U, (input & 0x01U) == 0x01U);
        }

        /// <summary>
        ///
        /// </summary>
        /// <remarks>GF(2 ^ 6) multiply (for Reed-Solomon encoder).</remarks>
        /// <param name="a"></param>
        /// <param name="b"></param>
        /// <returns></returns>
        private byte gf6Mult(byte a, byte b)
        {
            byte p = 0x00;

            for (uint i = 0U; i < 6U; i++) {
                if ((b & 0x01) == 0x01)
                    p ^= a;

                a <<= 1;

                if ((a & 0x40) == 0x40)
                    a ^= 0x43;              // primitive polynomial : x ^ 6 + x + 1

                b >>= 1;
            }

            return p;
        }
    } // internal sealed class ReedSolomonEncoder
} // namespace fnecore.EDAC.RS