www.pudn.com > LZ77.rar > Dictionary.cpp

// Dictionary.cpp: implementation of the CDictionary class. 
// 
////////////////////////////////////////////////////////////////////// 
 
/* 
	Created by: Luria Israel 
 
  This project implements the use of a dynamic LZW compression. 
  This code is free for use, and can be inserted into any MFC project. 
*/ 
 
#include "stdafx.h" 
#include "Dictionary.h" 
 
#ifdef _DEBUG 
#undef THIS_FILE 
static char THIS_FILE[]=__FILE__; 
#define new DEBUG_NEW 
#endif 
 
////////////////////////////////////////////////////////////////////// 
// Construction/Destruction 
////////////////////////////////////////////////////////////////////// 
 
CDictionary::CDictionary() 
{ 
} 
 
CDictionary::~CDictionary() 
{ 
	ClearDictionary(); 
} 
 
void CDictionary::ClearDictionary() 
{ 
	//	Go over every element in the dictionary and delete it 
	dicElement *temp = NULL; 
 
	while (GetSize() > 0) 
	{ 
		temp = (dicElement*)GetAt(0); 
		RemoveAt(0); 
		delete[] temp; 
	} 
} 
 
DWORD CDictionary::AddEntry(DWORD prefix, BYTE letter) 
{ 
	//	Add a dictionary element. 
	//	Since the dictionary should already have all the values 
	//	between 0-255, we start it from 256. 
	dicElement *temp = new dicElement; 
 
	temp->m_Prefix = prefix; 
	temp->m_Letter = letter; 
 
	Add(temp); 
 
	return GetSize() + 255; 
} 
 
long CDictionary::GetEntry(DWORD prefix, BYTE letter) 
{ 
	//	Returns the code of an element from the dictionary 
	//	by searching for the prefix and letter assosiated with 
	//	that element code. 
	 
	//	Returns -1 if no entry was found 
	int total = GetSize(); 
	dicElement *temp = NULL; 
 
	for (int counter = 0; counter < total; counter++) 
	{ 
		temp = (dicElement*)GetAt(counter); 
 
		if ((temp->m_Prefix == prefix) &&  
			(temp->m_Letter == letter)) 
		{ 
			break; 
		} 
		temp = NULL; 
	} 
 
	if (temp != NULL) 
		return counter + 256; 
	else 
		return -1; 
} 
 
BOOL CDictionary::IsCodeExist(DWORD code) 
{ 
	//	Check if the code exist in the dictionary 
	//	Returns TRUE if so, and FALSE if not. 
	DWORD returnValue = 0; 
 
	//	If the code is lower then 256, then the element is a normal 
	//	ASCII character, and as such is considered to be in the 
	//	dictionay. 
	if (code < 256) 
		return TRUE; 
 
	returnValue = code - 256; 
	if (returnValue < (unsigned)GetSize()) 
		return TRUE; 
	else  
		return FALSE; 
} 
 
DWORD CDictionary::GetMaxCode() 
{ 
	//	Return the highest code in the dictionary 
	return GetSize() + 256; 
} 
 
void CDictionary::GetBytesFromCode(CByteArray *Buffer, DWORD code) 
{ 
	//	Fill an array with bytes using the code for retrieving  
	//	those bytes from the dictionary elements 
 
	//	Since we dont have 0-255 in the dictionary we have to make  
	//	sure, that if we get below 256 we stop (but still add that code) 
	//	Every code higher then 255, will have a letter attached to it, 
	//	which we use for getting the string back. 
	dicElement *tmpEl = NULL; 
 
	while (code > 255) 
	{ 
		tmpEl = (dicElement*)GetAt(code - 256); 
		Buffer->Add(tmpEl->m_Letter); 
		code = tmpEl->m_Prefix; 
	} 
	Buffer->Add((BYTE)code); 
}