#include <stdio.h>
#include <stdlib.h>

#ifdef _OPENMP
  #include <omp.h>
  #define TRUE  1
  #define FALSE 0
#else
  #define omp_get_thread_num() 0
  #define omp_get_num_threads() 1
#endif

#define SUM_INIT 0
double getCPU(void)
{
        return ((double) omp_get_wtime());
        }

int main()
{
   int nthr;
   int i, n = 2500000;
   float sum, a[n], n1=n;
   float ref = SUM_INIT + (n1-1)*n1/2.0;

#ifdef _OPENMP
   (void) omp_set_dynamic(FALSE);
   if (omp_get_dynamic()) {printf("Warning: dynamic adjustment of threads has been set\n");}
   //(void) omp_set_num_threads(8);
#endif

   for (i=0; i<n; i++)
       a[i] = i;

   #pragma omp parallel
   {
      nthr=omp_get_num_threads();
      #pragma omp single
      printf("Number of threads is %d\n",nthr);
   }

   double t0,t1;
   t0 = getCPU();
   sum = SUM_INIT;
   printf("Value of sum prior to parallel region: %g\n",sum);
   #pragma omp parallel for default(none) shared(n,a) \
               reduction(+:sum)
        for (i=0; i<n; i++)
          sum += a[i];
   /*-- End of parallel reduction --*/
   t1 = getCPU();
   (void) printf("Number threads %d Exec time %g sec\n", nthr, t1 - t0);

   printf("Value of sum after parallel region: %g\n",sum);
   printf("Check results: error = %g (should be %g)\n",(sum-ref)/ref,ref);


   return(0);

}