crc16.h

isdn的完整解决方案。非常强大。不过是国际标准而非国标。

// Crc16.h

#ifndef USHORT
#define USHORT	unsigned short
#endif

#ifndef BYTE
#define BYTE	unsigned char
#endif

#ifndef TRUE
#define TRUE	(1)
#endif

#ifndef FALSE
#define FALSE	(0)
#endif

#define BOOL int

/** This class provides functions for computing 16-bit CRC values.
* 	It implements both a slow bit-at-a-time method and a table-driven
* 	method.  The simple method was implemented as a way of verifying
* 	that the optimized table-method works.  
*
* POPULAR POLYNOMIALS
*
*	@li CCITT:	x^16 + x^12 + x^5 + x^0 (set m_Polynomial to 0x1021)
*	@li	CRC-16:	x^16 + x^15 + x^2 + x^0 (set m_Polynomial to 0x8005)
*
*
* REFLECTED INPUT/CRC
*
*	Reflected input and reflected CRC is common with serial interfaces.
*  This is because the least-significant-bit is typically transmitted 
*  first with serial interfaces.
*/



class CCrc16
{
public:
	CCrc16();
	USHORT	ReverseBits( USHORT x );
	BYTE	ReverseBits( BYTE b );
	void	SimpleNextByte( BYTE b );
	USHORT	SimpleComputeBlock( BYTE* data, int length );
	USHORT	SimpleGetCrc();
	USHORT	CreateTableEntry( int index );
	void	CreateTable();
	USHORT	ComputeCrcUsingTable(  BYTE* data, int length );

	USHORT	m_Crc;
	USHORT	m_ResetValue;
	USHORT	m_Polynomial;
	BOOL	m_Reflect;
	BOOL	m_ReflectCrc;
	USHORT	m_CrcXorOutput;
	USHORT	m_Table[256];
};