Crc16.h

//-------------------------------------------------------------------------------------
// CRC16 support class
// Based on various examples found on the web
// Copyright (C) 2014 Vincenzo Mennella (see license.txt)
// History
//  0.1.0 31/05/2014:   First public code release
//  0.1.1 17/12/2014:   Minor revision and commented code
//
// License
// "MIT Open Source Software License":
// Permission is hereby granted, free of charge, to any person obtaining a copy of
// this software and associated documentation files (the "Software"), to deal in the
// Software without restriction, including without limitation the rights to use, copy,
// modify, merge, publish, distribute, sublicense, and/or sell copies of the Software,
// and to permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
// FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
// COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
// IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//-------------------------------------------------------------------------------------
#ifndef CRC16_H
#define CRC16_H
#define LIBRARY_VERSION_CRC16_H   "0.1.1"

class Crc16 {
   private:
        //Crc parameters
        uint16_t _msbMask;
        uint16_t _mask;
        uint16_t _xorIn;
        uint16_t _xorOut;
        uint16_t _polynomial;
        uint8_t _reflectIn;
        uint8_t _reflectOut;
        //Crc value
		uint16_t _crc;
		uint8_t reflect(uint8_t data, uint8_t bits = 32);

   public:
        inline Crc16()
        {
            //Default to XModem parameters
            _reflectIn = false;
            _reflectOut = false;
            _polynomial = 0x1021;
            _xorIn = 0x0000;
            _xorOut = 0x0000;
            _msbMask = 0x8000;
            _mask = 0xFFFF;
            _crc = _xorIn;
        }
        inline Crc16(uint8_t reflectIn, uint8_t reflectOut, uint16_t polynomial, uint16_t xorIn, uint16_t xorOut, uint16_t msbMask, uint16_t mask)
        {
            _reflectIn = reflectIn;
            _reflectOut = reflectOut;
            _polynomial = polynomial;
            _xorIn = xorIn;
            _xorOut = xorOut;
            _msbMask = msbMask;
            _mask = mask;
            _crc = _xorIn;
        }
        inline void clearCrc();
        inline void updateCrc(uint8_t data);
        inline uint16_t getCrc();
        inline uint32_t fastCrc(uint8_t data[], uint8_t start, uint16_t length, uint8_t reflectIn, uint8_t reflectOut, uint16_t polynomial, uint16_t xorIn, uint16_t xorOut, uint16_t msbMask, uint16_t mask);
        inline uint32_t XModemCrc(uint8_t data[], uint8_t start, uint16_t length)
		{
            //  XModem parameters: poly=0x1021 init=0x0000 refin=false refout=false xorout=0x0000
            return fastCrc(data, start, length, false, false, 0x1021, 0x0000, 0x0000, 0x8000, 0xffff);
		}
};

//---------------------------------------------------
// Initialize crc calculation
//---------------------------------------------------
void Crc16::clearCrc()
{
	_crc = _xorIn;
}
//---------------------------------------------------
// Update crc with new data
//---------------------------------------------------
void Crc16::updateCrc(uint8_t data)
{
	if (_reflectIn != 0)
		data = (uint8_t) reflect(data, 8);

	int j = 0x80;

	while (j > 0)
	{
		uint16_t bit = (uint16_t)(_crc & _msbMask);
		
		_crc <<= 1;

		if ((data & j) != 0)
		{
			bit = (uint16_t)(bit ^ _msbMask);
		}

		if (bit != 0)
		{
			_crc ^= _polynomial;
		}

		j >>= 1;
	}
}

//---------------------------------------------------
// Get final crc value
//---------------------------------------------------
uint16_t Crc16::getCrc()
{
  if (_reflectOut != 0)
		_crc = (uint32_t)((reflect(_crc) ^ _xorOut) & _mask);

	return _crc;
}

//---------------------------------------------------
// Calculate generic crc code on data array
// Examples of crc 16:
// Kermit: 		width=16 poly=0x1021 init=0x0000 refin=true  refout=true  xorout=0x0000 check=0x2189
// Modbus: 		width=16 poly=0x8005 init=0xffff refin=true  refout=true  xorout=0x0000 check=0x4b37
// XModem: 		width=16 poly=0x1021 init=0x0000 refin=false refout=false xorout=0x0000 check=0x31c3
// CCITT-False:	width=16 poly=0x1021 init=0xffff refin=false refout=false xorout=0x0000 check=0x29b1
//---------------------------------------------------
uint32_t Crc16::fastCrc(uint8_t data[], uint8_t start, uint16_t length, uint8_t reflectIn, uint8_t reflectOut, uint16_t polynomial, uint16_t xorIn, uint16_t xorOut, uint16_t msbMask, uint16_t mask)
{
	uint32_t crc = xorIn;

	int j;
	uint8_t c;
	uint32_t bit;

	if (length == 0) return crc;

	for (int i = start; i < (start + length); i++)
	{
		c = data[i];

		if (reflectIn != 0)
			c = (uint8_t) reflect(c, 8);

		j = 0x80;

		while (j > 0)
		{
			bit = (uint32_t)(crc & msbMask);
			crc <<= 1;

			if ((c & j) != 0)
			{
				bit = (uint32_t)(bit ^ msbMask);
			}

			if (bit != 0)
			{
				crc ^= polynomial;
			}

			j >>= 1;
		}
	}

	if (reflectOut != 0)
		crc = (uint32_t)((reflect(crc) ^ xorOut) & mask);

	return crc;
}

//-------------------------------------------------------
// Reflects bit in a uint8_t
//-------------------------------------------------------
uint8_t Crc16::reflect(uint8_t data, uint8_t bits)
{
	unsigned long reflection = 0x00000000;
	// Reflect the data about the center bit.
	for (uint8_t bit = 0; bit < bits; bit++)
	{
		// If the LSB bit is set, set the reflection of it.
		if ((data & 0x01) != 0)
		{
			reflection |= (unsigned long)(1 << ((bits - 1) - bit));
		}

		data = (uint8_t)(data >> 1);
	}

	return reflection;
}
#endif