fmi.h

自适应算术编码。这个项目假设读者已经了解基本的算术压缩编码的概念。

#ifndef __FREQUENCY_MODEL_CLASS_DECLARATION__
#define __FREQUENCY_MODEL_CLASS_DECLARATION__

//	DWORD type declaration
#ifndef DWORD
#define DWORD				unsigned long
#endif
//	Frequency value limit
#define FMI_OVERFLOW_LIMIT		((DWORD)1 << 30)

class CFreqModIncr
{

public:

//	Purpose :			construction
	CFreqModIncr()
		: m_dwIncrement(0)
		, m_pdwTable(0)
	{}

//	Purpose :			destruction
	virtual ~CFreqModIncr()
	{	if (m_pdwTable) delete [] m_pdwTable;	}

//	Purpose :			call to get total frequency of the model
//	Returns :			the total frequency of the model
	DWORD GetTotalFrequency()
	{	return m_pdwTable[0];	}

//	Purpose :			call to initialize the model
//	Arguments :
//		dwTotal			= total number of elements to track
	void Initialize(DWORD dwTotal);

//	Purpose :			call to uninitialize the model
	void Uninitialize();

//	Purpose :			call to increase element's frequency and obtain
//						the element's frequency interval bounds
//	Arguments :
//		dwIndex			= index of the element
//		rdwLeftBound	= reference to a variable to keep the left bound
//		rdwRightBound	= reference to a variable to keep the right bound
	void PassByIndex(
		DWORD dwIndex,
		DWORD &rdwLeftBound,
		DWORD &rdwRightBound);

//	Purpose :			call to obtain the element whose frequency interval contains
//						a given point and to increase the element's frequency
//	Returns :			the index of an element found
//	Arguments :
//		dwPoint			= a given point
//		rdwLeftBound	= reference to a variable to keep the left bound
//		rdwRightBound	= reference to a variable to keep the right bound
	DWORD PassByPoint(
		DWORD dwPoint,
		DWORD &rdwLeftBound,
		DWORD &rdwRightBound);

//	The value to increment frequencies by
	DWORD m_dwIncrement;

protected:

//	Total number of elements
	DWORD m_dwTotal;
//	Internal displacement start value
	DWORD m_dwStartAddend;
//	Frequency table in internal format
	DWORD *m_pdwTable;

private:

//	Purpose :			called to keep frequencies nonzeroes, before
//						reducing or upon initializing the model
	void AdjustFrequencies();

//	Purpose :			called to prevent overflows, halves the frequencies
	void ReduceByHalf();

};

#endif // __FREQUENCY_MODEL_CLASS_DECLARATION__