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GammaCompress.hpp

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/*==========================================================================
 * Copyright (c) 2001 Carnegie Mellon University.  All Rights Reserved.
 *
 * Use of the Lemur Toolkit for Language Modeling and Information Retrieval
 * is subject to the terms of the software license set forth in the LICENSE
 * file included with this software, and also available at
 * http://www.cs.cmu.edu/~lemur/license.html
 *
 *==========================================================================
*/


#ifndef _GAMMACOMPRESSH_
#define _GAMMACOMPRESSH_


//---------------------------------------------------------------

//  J. Lafferty, 10/29/00
//
//---------------------------------------------------------------

#include "common_headers.hpp"
#include "Compress.hpp"

class GammaCompress : public Compress 
{
public:
  GammaCompress();
  virtual ~GammaCompress(){}
  
public:
  void compress (ostream &os, int n, int * a);
  int decompress (istream &is, int * a);
  int read(istream &is);
  const string type() { return "gamma";  }

private:
  void initBitMasks ();
  int floorlog2 (double x);
  int gamma_size(int x);
  int gamma_encode(int x, int offset, vector<int> &bv);
  int gamma_decode(int * y, int offset, vector<int> &bv);
  int read_bits(istream & is, vector<int> &bv, int size);
  void write_bits(ostream & os, vector<int> &bv);

private:
  vector<int> bv;  
  static char bits[8];
};

#endif

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