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47 lines
1.5 KiB
47 lines
1.5 KiB
/*
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* Copyright (C) 2009,2013 by Jonathan Naylor, G4KLX
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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; version 2 of the License.
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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 for more details.
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*/
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#ifndef DStarScrambler_H
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#define DStarScrambler_H
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/*
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* D-Star bit scrambler applied to the physical RF layer.
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*
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* The D-Star standard mandates scrambling of the bit stream before GMSK
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* modulation to randomise the data and avoid long runs of identical bits that
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* would stress the PLL in receivers. The scrambler uses a linear feedback
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* shift register with the polynomial x^17 + x^12 + 1.
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*
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* process() operates in-place (inOut form) or with separate input/output
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* buffers, and handles both bit-per-bool and packed-byte representations.
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* reset() resets the LFSR to its initial state.
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*/
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class CDStarScrambler {
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public:
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CDStarScrambler();
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~CDStarScrambler();
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void process(bool* inOut, unsigned int length);
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void process(const bool* in, bool* out, unsigned int length);
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void process(unsigned char* inOut, unsigned int length);
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void process(const unsigned char* in, unsigned char* out, unsigned int length);
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void reset();
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private:
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unsigned int m_count; // Current position in the LFSR sequence.
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};
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#endif
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