EvtPredGen.hh

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* Copyright 1998-2020 CERN for the benefit of the EvtGen authors       *
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* This file is part of EvtGen.                                         *
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* GNU General Public License for more details.                         *
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#ifndef EVT_PRED_GEN_HH
#define EVT_PRED_GEN_HH
 
#include <stdio.h>
 
// A predicate is applied to a generator to get another generator.
// Accept-reject can be implemented in this way.
//
//           Predicate
// Generator    ->     Generator
 
template <class Generator, class Predicate>
class EvtPredGen {
  public:
    typedef typename Generator::result_type result_type;
 
    EvtPredGen() : m_tried( 0 ), m_passed( 0 ) {}
 
    EvtPredGen( Generator gen, Predicate pred ) :
        m_gen( gen ), m_pred( pred ), m_tried( 0 ), m_passed( 0 )
    {
    }
 
    EvtPredGen( const EvtPredGen& other ) :
        m_gen( other.m_gen ),
        m_pred( other.m_pred ),
        m_tried( other.m_tried ),
        m_passed( other.m_passed )
    {
    }
 
    ~EvtPredGen() {}
 
    result_type operator()()
    {
        int i = 0;
        int MAX = 10000;
        while ( i++ < MAX ) {
            m_tried++;
            result_type point = m_gen();
            if ( m_pred( point ) ) {
                m_passed++;
                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 m_gen();
    }
 
    inline int getTried() const { return m_tried; }
    inline int getPassed() const { return m_passed; }
 
  protected:
    Generator m_gen;
    Predicate m_pred;
    int m_tried;
    int m_passed;
};
 
#endif