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106 lines
3.7 KiB
C++
106 lines
3.7 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2020 Jon Beniston, M7RCE //
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// //
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// This program is free software; you can redistribute it and/or modify //
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// it under the terms of the GNU General Public License as published by //
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// the Free Software Foundation as version 3 of the License, or //
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// (at your option) any later version. //
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// //
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// This program is distributed in the hope that it will be useful, //
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// but WITHOUT ANY WARRANTY; without even the implied warranty of //
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
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// GNU General Public License V3 for more details. //
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// //
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// You should have received a copy of the GNU General Public License //
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// along with this program. If not, see <http://www.gnu.org/licenses/>. //
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///////////////////////////////////////////////////////////////////////////////////
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#ifndef INCLUDE_LFSR_H
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#define INCLUDE_LFSR_H
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#include <stdint.h>
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#include "export.h"
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// Linear feedback shift register that can be used for scrambling or generating
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// PN (Pseudo Noise) random sequence.
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class SDRBASE_API LFSR
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{
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public:
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// Create and initialise LFSR with specified number of bits, polynomial and
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// initial state (which must be non-zero, unless a multiplicative scrambler).
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// The +1 is implicit in the polynomial so x^1 + 1 should be passed as 0x01
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LFSR(uint32_t polynomial, uint32_t init_value = ~0U, int rand_bit = -1) :
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m_rand_bit(rand_bit),
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m_polynomial(polynomial),
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m_init_value(init_value)
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{
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init();
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}
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// Initialise LFSR state
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void init()
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{
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m_sr = m_init_value;
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}
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// Shift the LFSR one bit and return output of XOR
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int shift();
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// Multiplicative scramble a single bit using LFSR
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int scramble(int bit_in);
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// Multiplicative scramble of data using LFSR - LSB first
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void scramble(uint8_t *data, int length);
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// Descramble data using LFSR - LSB first
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void descramble(uint8_t *data, int length);
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// XOR data with rand_bit from LFSR generating pseudo noise (PN) sequence - LSB first
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void randomize(uint8_t *data, int length);
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// Get current shift-register value
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uint32_t getSR()
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{
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return m_sr;
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}
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// Set the polynomial
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void setPolynomial(uint32_t polynomial)
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{
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m_polynomial = polynomial;
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}
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// Get the polynomial
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uint32_t getPolynomial()
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{
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return m_polynomial;
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}
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private:
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int m_rand_bit; // Which bit from the SR to use in randomize()
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uint32_t m_polynomial; // Polynomial coefficients (+1 is implicit)
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uint32_t m_init_value; // Value to initialise SR to when init() is called
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uint32_t m_sr; // Shift register
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};
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// http://www.jrmiller.demon.co.uk/products/figs/man9k6.pdf
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// In Matlab: comm.Scrambler(2, '1 + z^-12 + z^-17', 0)
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// Call scramble()
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class SDRBASE_API ScramblerG3RUG : public LFSR
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{
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public:
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ScramblerG3RUG() : LFSR(0x10800, 0x0) {}
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};
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// https://public.ccsds.org/Pubs/131x0b3e1.pdf
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// x^8+x^7+x^5+x^3+1
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// In Matlab: comm.PNSequence('Polynomial', 'x^8+x^7+x^5+x^3+1', 'InitialConditions', [1 1 1 1 1 1 1 1])
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// Call randomize()
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class SDRBASE_API RandomizeCCSDS : public LFSR
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{
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public:
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RandomizeCCSDS() : LFSR(0x95, 0xff, 7) {}
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};
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#endif
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