Re: on a design question using C++

From:

"nvinhphu@gmail.com" <nvinhphu@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 7 Feb 2009 01:42:15 -0800 (PST)

Message-ID:

<8900a3d6-e18e-4dfb-91f0-98d218671be7@f3g2000yqf.googlegroups.com>

Hi all,

Thanks to all your support, I managed to write that code. Here it is:

#include <iostream>
#include <math.h>
#include <boost/shared_ptr.hpp>

using namespace std;
using boost::shared_ptr;

class LinearSoftening
{
  public:

             LinearSoftening

               ( double ki, double kc )

         : ki_(ki), kc_(kc) {}

   double evalFunc ( double x ) { return ki_ + kc_ * x;}
   double evalDeri ( double x ) { return kc_;}

  private:

   double ki_;
   double kc_;
};

class ExponentialSoftening
{
  public:

             ExponentialSoftening

               ( double ki, double alpha, double beta )

          : ki_(ki), alpha_(alpha), beta_(beta){}

   double evalFunc ( double x )
   {
     return ki_ + exp( 1. - alpha_ + beta_ * x );
   }

   double evalDeri ( double x ) { return alpha_ + beta_;}

  private:

   double ki_;
   double alpha_;
   double beta_;
};

class SofteningLawInterface
{
  public:

    virtual double evalFunc ( double x ) = 0;
    virtual double evalDeri ( double x ) = 0;
};

template < class SofteningLawPolicy>
class SofteningLaw : public SofteningLawInterface
{
  public:

                       SofteningLaw

                ( const SofteningLawPolicy& policy ) : policy_(policy)
{};

    double evalFunc ( double x ){ return policy_.evalFunc(x);}
    double evalDeri ( double x ){ return policy_.evalDeri(x);}

  private:

   SofteningLawPolicy policy_;
};

class Application
{
  public:

   double computeDamage ( double kappa )
   {
     return softLaw_->evalFunc ( kappa );
   }

   double computeDeriOfDamage ( double kappa )
   {
     return softLaw_->evalDeri ( kappa );
   }

   template <class SoftLawPolicy>
   void setSofteningLaw ( const SoftLawPolicy& policy )
   {
     softLaw_.reset ( new SofteningLaw<SoftLawPolicy>(policy) );
   }

  private:

   shared_ptr<SofteningLawInterface> softLaw_;
};

int main ()
{
  // compile time

  typedef SofteningLaw<LinearSoftening> LinearSoftLaw;
  typedef SofteningLaw<ExponentialSoftening> ExponeSoftLaw;

  LinearSoftening linearSoft(10., 50.);
  ExponentialSoftening exponeSoft(10., 0.99, 100.);

  LinearSoftLaw linear(linearSoft);
  ExponeSoftLaw expone(exponeSoft);

  // run time

  Application app;

  app.setSofteningLaw( linear );

  // compare performance

  const int n = 1000000000;

  for ( int i = 0; i < n; i++ )
  {
    //double fval1 = linear.evalFunc(0.1);
    //double fder1 = linear.evalDeri(0.1);

    //cout << " fval1: " << fval1 << ", fderi1: " << fder1 << "\n";

    double fval2 = app.computeDamage (0.1);
    double fder2 = app.computeDeriOfDamage (0.1);

    //cout << " fval2: " << fval2 << ", fderi2: " << fder2 << "\n";
  }

  return 0;
}

I did a performance comparison between object defined at compile time
and at run time,
the result is that the latter is slower than the former:

real 0m43.238s
user 0m43.127s
sys 0m0.088s

real 1m28.149s
user 1m27.965s
sys 0m0.152s

Since I am calling this code in a tight loop, I think that I have to
fall back to the
first approach. But I then lose the beauty and clarity of template
code.

Thanks a lot again.

Phu