EvtPredGen.hh

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/*******************************************************************************
 * Project: BaBar detector at the SLAC PEP-II B-factory
 * Package: EvtGenBase
 *    File: $Id: EvtPredGen.hh,v 1.1.1.2 2007/10/26 05:03:14 pingrg Exp $
 *  Author: Alexei Dvoretskii, dvoretsk@slac.stanford.edu, 2001-2002
 *
 * Copyright (C) 2002 Caltech
 *******************************************************************************/
 
// A predicate is applied to a generator to get another generator.
// Accept-reject can be implemented in this way.
//
//           Predicate
// Generator    ->     Generator
 
#ifndef EVT_PRED_GEN_HH
#define EVT_PRED_GEN_HH
 
#include <stdio.h>
 
template <class Generator, class Predicate> class EvtPredGen {
 
public:
  typedef typename Generator::result_type result_type;
 
  EvtPredGen() : itsTried( 0 ), itsPassed( 0 ) {}
 
  EvtPredGen( Generator gen, Predicate pred )
      : itsGen( gen ), itsPred( pred ), itsTried( 0 ), itsPassed( 0 ) {}
 
  EvtPredGen( const EvtPredGen& other )
      : itsGen( other.itsGen )
      , itsPred( other.itsPred )
      , itsTried( other.itsTried )
      , itsPassed( other.itsPassed ) {}
 
  ~EvtPredGen() {}
 
  result_type operator()() {
 
    int i   = 0;
    int MAX = 10000;
    while ( i++ < MAX )
    {
 
      itsTried++;
      result_type point = itsGen();
      if ( itsPred( point ) )
      {
        itsPassed++;
        return point;
      }
    }
 
    printf( "No random point generated after %d attempts\n", MAX );
    printf( "Sharp peak? Consider using pole compensation.\n" );
    printf( "I will now pick a point at random to return.\n" );
    return itsGen();
  }
 
  inline int getTried() const { return itsTried; }
  inline int getPassed() const { return itsPassed; }
 
protected:
  Generator itsGen;
  Predicate itsPred;
  int       itsTried;
  int       itsPassed;
};
 
#endif