/////////////////////////////////////////////////////////////////////////////////// // Copyright (C) 2020 Jon Beniston, M7RCE // // // // 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 as version 3 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 V3 for more details. // // // // You should have received a copy of the GNU General Public License // // along with this program. If not, see . // /////////////////////////////////////////////////////////////////////////////////// #ifndef INCLUDE_LFSR_H #define INCLUDE_LFSR_H #include #include "export.h" // Linear feedback shift register that can be used for scrambling or generating // PN (Pseudo Noise) random sequence. class SDRBASE_API LFSR { public: // Create and initialise LFSR with specified number of bits, polynomial and // initial state (which must be non-zero, unless a multiplicative scrambler). // The +1 is implicit in the polynomial so x^1 + 1 should be passed as 0x01 LFSR(uint32_t polynomial, uint32_t init_value = ~0U, int rand_bit = -1) : m_rand_bit(rand_bit), m_polynomial(polynomial), m_init_value(init_value) { init(); } // Initialise LFSR state void init() { m_sr = m_init_value; } // Shift the LFSR one bit and return output of XOR int shift(); // Multiplicative scramble a single bit using LFSR int scramble(int bit_in); // Multiplicative scramble of data using LFSR - LSB first void scramble(uint8_t *data, int length); // Descramble data using LFSR - LSB first void descramble(uint8_t *data, int length); // XOR data with rand_bit from LFSR generating pseudo noise (PN) sequence - LSB first void randomize(uint8_t *data, int length); // Get current shift-register value uint32_t getSR() { return m_sr; } // Set the polynomial void setPolynomial(uint32_t polynomial) { m_polynomial = polynomial; } // Get the polynomial uint32_t getPolynomial() { return m_polynomial; } private: int m_rand_bit; // Which bit from the SR to use in randomize() uint32_t m_polynomial; // Polynomial coefficients (+1 is implicit) uint32_t m_init_value; // Value to initialise SR to when init() is called uint32_t m_sr; // Shift register }; // http://www.jrmiller.demon.co.uk/products/figs/man9k6.pdf // In Matlab: comm.Scrambler(2, '1 + z^-12 + z^-17', 0) // Call scramble() class SDRBASE_API ScramblerG3RUG : public LFSR { public: ScramblerG3RUG() : LFSR(0x10800, 0x0) {} }; // https://public.ccsds.org/Pubs/131x0b3e1.pdf // x^8+x^7+x^5+x^3+1 // In Matlab: comm.PNSequence('Polynomial', 'x^8+x^7+x^5+x^3+1', 'InitialConditions', [1 1 1 1 1 1 1 1]) // Call randomize() class SDRBASE_API RandomizeCCSDS : public LFSR { public: RandomizeCCSDS() : LFSR(0x95, 0xff, 7) {} }; // 802.15.4 GFSK PHY // Call randomize() class SDRBASE_API Randomize_802_15_4_PN9 : public LFSR { public: Randomize_802_15_4_PN9() : LFSR(0x108, 0x1fe, 0) {} }; #endif