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context.h

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/***************************************************************************
    context.h  -  Definition of Context class.
                             -------------------
    begin                : June 21 2002
    copyright            : (C) 2003 by Vojtìch Toman
    email                : vtoman@lit.cz
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/

/* Based on code by:                                                       */

/***************************************************************************
Authors:        John Carpenelli   (johnfc@ecr.mu.oz.au)
                Wayne Salamonsen  (wbs@mundil.cs.mu.oz.au)

Purpose:        Data compression using a word-based model and revised 
                arithmetic coding method.

Based on:       A. Moffat, R. Neal, I.H. Witten, "Arithmetic Coding Revisited",
                Proc. IEEE Data Compression Conference, Snowbird, Utah, 
                March 1995.


Copyright 1995 John Carpinelli and Wayne Salamonsen, All Rights Reserved.

These programs are supplied free of charge for research purposes only,
and may not sold or incorporated into any commercial product.  There is
ABSOLUTELY NO WARRANTY of any sort, nor any undertaking that they are
fit for ANY PURPOSE WHATSOEVER.  Use them at your own risk.  If you do
happen to find a bug, or have modifications to suggest, please report
the same to Alistair Moffat, alistair@cs.mu.oz.au.  The copyright
notice above and this statement of conditions must remain an integral
part of each and every copy made of these files.
****************************************************************************/


#ifndef CONTEXT_H
#define CONTEXT_H


#ifdef __GNUG__
# pragma interface
#endif


#include <cstdlib>              //for free() and malloc()


#include "defs.h"
#include "contextbase.h"



//#define CHAR_CONTEXT_LENGTH   256


#define BACK(i)                 ((i) & ((i) - 1))

#define FORW(i)                 ((i) + ((i) & - (i)))


#define MAX_FREQUENCY           ((FreqValue) 1 << F_BITS)


#define MIN_INCR                1



#define MOST_PROB_AT_END        1








class Context : public ContextBase
{
public:
  Context(void);

  Context(int, ContextType);

  virtual ~Context(void);

  virtual void setType(int, ContextType);

  virtual int initialize(void);

  virtual int lastFixedSymbol(void);

  virtual int encode(int) throw (ExaltContextNotInitializedException, ExaltIOException);

  virtual int encodeEndOfMessage() throw (ExaltContextNotInitializedException, ExaltIOException);

  virtual int decode(void) throw (ExaltContextNotInitializedException, ExaltIOException);

  virtual void purgeContext(void);

  virtual int installSymbol(int);

protected:
  int initialSize;

  int maxLength, length;

  FreqValue nSingletons;

  ContextType type;

  int nSymbols;

  FreqValue total;

  FreqValue *tree;

  FreqValue incr;

  int mostFreqSymbol;

  FreqValue mostFreqCount;

  FreqValue mostFreqPos;


  virtual void getInterval(FreqValue *, FreqValue *, int);

  virtual void halveContext(void);

  virtual void initZeroFreq();

}; //Context


#endif //CONTEXT_H

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