/*
 *	Copyright (C) 2009,2013 by Jonathan Naylor, G4KLX
 *
 *	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; version 2 of the License.
 *
 *	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.
 */

#ifndef	DStarScrambler_H
#define	DStarScrambler_H

/*
 * D-Star bit scrambler applied to the physical RF layer.
 *
 * The D-Star standard mandates scrambling of the bit stream before GMSK
 * modulation to randomise the data and avoid long runs of identical bits that
 * would stress the PLL in receivers.  The scrambler uses a linear feedback
 * shift register with the polynomial x^17 + x^12 + 1.
 *
 * process() operates in-place (inOut form) or with separate input/output
 * buffers, and handles both bit-per-bool and packed-byte representations.
 * reset() resets the LFSR to its initial state.
 */
class CDStarScrambler {
public:
	CDStarScrambler();
	~CDStarScrambler();

	void process(bool* inOut, unsigned int length);
	void process(const bool* in, bool* out, unsigned int length);

	void process(unsigned char* inOut, unsigned int length);
	void process(const unsigned char* in, unsigned char* out, unsigned int length);

	void reset();

private:
	unsigned int m_count;   // Current position in the LFSR sequence.
};

#endif