piomp.c

piomp.c

#include <stdio.h>
#include <omp.h>

static long num_steps = 99999999;
double step,start = 0.0,stop = 0.0;

#define NUM_THREADS 8
int main ()
{
    double pi;
    step = 1.0/(double) num_steps;
    omp_set_num_threads(NUM_THREADS);

    #pragma omp parallel
    {
        int i, id,nthrds,nthreads = 0; double x, sum;
        id = omp_get_thread_num();
        nthrds = omp_get_num_threads();
        if (id == 0) nthreads = nthrds;

        printf("HELLO FROM THREAD %d\n", id);
        start = omp_get_wtime();
        for (i=id, sum=0.0;i< num_steps; i=i+NUM_THREADS)
        {
            x = (i+0.5)*step;
            sum += 4.0/(1.0+x*x);
        }

        sum = sum*step;

        #pragma omp atomic
        pi += sum ;
    }

    stop = omp_get_wtime();
    printf("pi = %f",pi);
    printf("time = %f",stop-start);
}