Reconstruction/MdcPatRec/MdcRecoUtil/include/MdcRecoUtil/ComPackExpFloat.h

Go to the documentation of this file.

//--------------------------------------------------------------------------
// File and Version Information:
//      $Id: ComPackExpFloat.h,v 1.2 2009/12/23 02:59:56 zhangy Exp $
//
// Description:
//      class ComPackExpFloat; pack a floating (double) into a fixed range
//      mantissa with an exponential (power of 2) representation.  With this class, the values
//      stored at the start of the range have the best precision, which
//      gradually decreases to the worst precision when going to the opposite
//      range.  This is equivalent to flat packing of the log of the value,
//      but because the exponent storage space is variable, this class allows
//      the equivalent of scaling the (log) value.
//
// Environment:
//      Software developed for the BaBar Detector at the SLAC B-Factory.
//
// Author List:
//      Dave Brown         10/12/00
//
// Copyright Information:
//      Copyright (C) 2000 LBNL
//
// History:
//  Migration for BESIII MDC
//
//
//--------------------------------------------------------------------------
 
#ifndef COMPACKEXPFLOAT_HH
#define COMPACKEXPFLOAT_HH
 
#include "MdcRecoUtil/ComPackBase.h"
#include <iostream>
 
class ComPackExpFloat : public ComPackBase<double> {
 
public:
  // specify the storage space (number of total bits) and the maximum exponent.
  // The mantissa will be stored in the bits left over after storing the exponent
  // Note that the exponent is -UNSIGNED-.  Note that the stop and start values do
  // _not_ have to be monotonic; the order simply defines which end of the range
  // has the fine precision (start) vs coarse (stop).  The 'center' command will
  // use the start and stop values to define the (exact) range for unpacking data
  // (ie the packing bins will be centered about those values).
  ComPackExpFloat( unsigned nbits, unsigned maxexponent, double start, double stop,
                   bool center = false );
  virtual ~ComPackExpFloat();
  // ComPackBase functions
  virtual StatusCode pack( const double, d_ULong& ) const;
  virtual StatusCode unpack( const d_ULong, double& ) const;
  void               print( std::ostream& os ) const;
 
private:
  unsigned _maxexp;   // maximum value of the exponent (+1)
  unsigned _expmsk;   // exponent storage mask
  unsigned _mansft;   // mantissa storage shift
  unsigned _manmsk;   // mantissa storage mask
  unsigned _maxman;   // maximum integer mantissa
  double   _invrange; // inverse range
                      // pre-computed quantities to speed unpacking
  double* _expfac;
  double* _expoff;
  // disallow copy and equivalence
  ComPackExpFloat( const ComPackExpFloat& );
  ComPackExpFloat& operator=( const ComPackExpFloat& );
};
 
#endif