/*
 *	Copyright (C) 2009,2011,2014 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	CCITTChecksumReverse_H
#define	CCITTChecksumReverse_H

#include <cstdint>

/*
 * CCITT-16 checksum with reversed bit order, as required by the D-Star
 * radio header format and the DSRP network protocol.
 *
 * The API is identical to CCCITTChecksum; only the polynomial bit ordering
 * differs.  This variant is used whenever a checksum is appended to or
 * verified in a D-Star header (CHeaderData, DSRP header packets, .dvtool
 * file headers, slow-data header blocks).
 */
class CCCITTChecksumReverse {
public:
	CCCITTChecksumReverse();
	~CCCITTChecksumReverse();

	void update(const unsigned char* data, unsigned int length);

	void result(unsigned char* data);

	bool check(const unsigned char* data);

	void reset();

private:
	union {
		uint16_t m_crc16;
		uint8_t  m_crc8[2U];
	};
};

#endif