LZ77.rar Dictionary.cpp

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// 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) &amt;&amt;
(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);
}