template<word P>
class CRC16MSBF
{
public:
	
	class Table
	{
	public:
		static const word size = 1 << 8;
		Table()
		{
			for(word i = 0; i < size; i++)
			{
				word crc = i << 8;
				for(int b = 0; b < 8; b++)
					crc = (crc & 0x8000) ? ((crc << 1) ^ P) : (crc << 1);
				t[i] = crc;
			}
		}
		word t[size];
	};

	CRC16MSBF (word init = word(-1))
		: t(Single<Table>())
	{ Init(init); }

	inline void Add(byte data) { crc = (crc << 8) ^ t.t[ (crc >> 8) ^ data ]; }

	void Add(const byte* pdata, int size)
	{
		const byte* pde = pdata + size;
		while(pdata < pde) Add(*pdata++);	
	}
	
	inline CRC16MSBF& operator <<= (byte data) { Add(data); return *this; }

#ifdef CPU_LE
	word Value() const { return word( (crc >> 8) | (crc << 8) ); }
#endif
#ifdef CPU_BE
	word Value() const { return crc; }
#endif

	word Raw() const { return crc; }
	String Serialized() const { String s; word c = Value(); s.Cat(c & 0xFF); s.Cat(c >> 8); return s; } 

	bool IsValid() const { return (crc == 0); }
	word Invalidate() { return ++crc; }
	
	void Init(word in) { crc = init = in; }
	void Reset() { crc = init; }
	
	const Table& t;
	word crc;
	word init;
};

void TestCRC()
{
	String s = "This is a soon to be protected string!";
	
	CRC16LSBF_CCITT crc; //a common init value must be used, generally 0xFFFF..
	
	//process some data, more data could be added
	crc.Add((const byte*)s.Begin(), s.GetLength());
	
	//append crc value to the protected string if it should be included in check later
	//this is typical for hardware implementations.
	//software usually tests for equality, but it is esier in first case
	//since a packet can be checked as a whole.
	s << crc.Serialized();

	
	//transmit s, receiver checks it
	
	crc.Reset(); //here we just reuse the crc with its specified init value

	//check now includes the crc value appended	
	crc.Add((const byte*)s.Begin(), s.GetLength());

	ASSERT(crc.IsValid());
	
	//imagine a corrupt data stream
	s.Set(0,0);	

	crc.Reset(); //here we just reuse the crc

	//check now includes the crc value appended	
	crc.Add((const byte*)s.Begin(), s.GetLength());
	
	//now the stream must be invalid
	ASSERT(!crc.IsValid());
}