mc_pi_omp.c

// *******************************************************************
#pragma GCC optimize("O3","unroll-loops","omit-frame-pointer","inline", "unsafe-math-optimizations")
#pragma GCC option("arch=native","tune=native","no-zero-upper")
//************************************************************

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <limits.h>
#include <omp.h>
#define SEED 1053608
#define N 5000000000000

unsigned int seed = 676767676 ; 


//Random number generator with linear congruential generator
double randUint( long i ){
    
	seed = seed * 1103515245 + 123456;
    
    return seed / (double)UINT_MAX ;
}


int main()
{
   
    long count=0;
    double pi;
    
    //Init Parallelazation with reduction techinue
    #pragma omp parallel for reduction(+: count)
    for (long i=0; i<N; i++) {

        
        //Getting the coordinates y,x ε [0,1]
        double x,y;
        x = randUint(i);
        y = randUint(i);

        //Checking if in unit circle
        if (x*x+y*y <= 1)
            count = count + 1;

    
    }

    //Calcuting the ratio and as a result the pi
    pi=((double)count/(double)N) * 4.0;

    printf("OpenMP : # of trials = %14ld , estimate of pi is %1.16f AND an absolute error of %g\n",N,pi,fabs(pi - M_PI));

    return 0;
}