//	Ex1121.cc	§ 11.2.1

//	Calculates a polynom at point x in two different ways
//		and compare the execution time

//		Try also option -O or -Ofast in compilation 
//		SGI   : CC -Ofast Polynom.cc -lfastm
//		LINUX : g++ -O3  Polynom.cc
//		 also   g++ -O3 -ffast-math Polynom.cc

//		a.out < input.1121

#include <iostream.h>
#include <time.h>		// contains clock()
#include <math.h>

int main()
{
 const int NRUN = 100000;	// number of test runs
 const int N = 20;		// highest degree in polynom
    double a[N+1];		// (N+1) coefficients
    double x,xk,s1,s2;
       int k,j;
    double time1=0.0, time2=0.0, tstart;	// time measurment
 
 cout << endl;
 cout << "Polynom calculation" << endl;
 cout << "  Read coeff" << endl;
 
 for ( k = 0; k <= N; k++ )
  {
   cin >> a[k];
  }

 cout << endl;
 cout << "  Read X" << endl;
 cout << "  x = "; cin >> x;
 cout << endl;

//	version a (slow)
			tstart = clock();
for (j=1; j<=NRUN; j++)
{
 s1 = 0.0;
 for ( k = 0; k <= N; k++)
  {
   xk  = pow(x,k);
   s1 += xk * a[k];
  }
}
			time1 += clock()-tstart;

//	version b (fast)

			tstart = clock();
for (j=1; j<=NRUN; j++)
{
 s2 = a[0];
 xk = 1.0;
 for ( k = 1; k <= N; k++)
  {
   xk *= x;
   s2 += xk * a[k];
  }
}
			time2 += clock()-tstart;

//	Rescale to get seconds
 			time1 = time1/CLOCKS_PER_SEC;
 			time2 = time2/CLOCKS_PER_SEC;

cout << "  s1 = " << s1 << "   (" << time1 << " sec.)" << endl;
cout << "  s2 = " << s2 << "   (" << time2 << " sec.)" << endl;

 cout << endl;
}