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/******************************************************************************
* lzsscomprs.h - definition of Class SWCompress used for data compression
*
* $Id: lzsscomprs.h,v 1.4 2002/10/01 19:52:40 dglassey Exp $
*
* Copyright 1998 CrossWire Bible Society (http://www.crosswire.org)
* CrossWire Bible Society
* P. O. Box 2528
* Tempe, AZ 85280-2528
*
* 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 version 2.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
*/
#ifndef LZSSCOMPRS_H
#define LZSSCOMPRS_H
#include <swcomprs.h>
#include <defs.h>
SWORD_NAMESPACE_START
// The following are constant sizes used by the compression algorithm.
//
// N - This is the size of the ring buffer. It is set
// to 4K. It is important to note that a position
// within the ring buffer requires 12 bits.
//
// F - This is the maximum length of a character sequence
// that can be taken from the ring buffer. It is set
// to 18. Note that a length must be 3 before it is
// worthwhile to store a position/length pair, so the
// length can be encoded in only 4 bits. Or, put yet
// another way, it is not necessary to encode a length
// of 0-18, it is necessary to encode a length of
// 3-18, which requires 4 bits.
//
// THRESHOLD - It takes 2 bytes to store an offset and
// a length. If a character sequence only
// requires 1 or 2 characters to store
// uncompressed, then it is better to store
// it uncompressed than as an offset into
// the ring buffer.
//
// Note that the 12 bits used to store the position and the 4 bits
// used to store the length equal a total of 16 bits, or 2 bytes.
#define N 4096
#define F 18
#define THRESHOLD 3
#define NOT_USED N
class SWDLLEXPORT LZSSCompress:public SWCompress
{
static unsigned char m_ring_buffer[N + F - 1];
static short int m_match_position;
static short int m_match_length;
static short int m_lson[N + 1];
static short int m_rson[N + 257];
static short int m_dad[N + 1];
void InitTree ();
void InsertNode (short int Pos);
void DeleteNode (short int Node);
public:
LZSSCompress ();
virtual ~ LZSSCompress ();
virtual void Encode (void);
virtual void Decode (void);
};
SWORD_NAMESPACE_END
#endif
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