/* =====================================================
   OpenMP example: find min in array
   ===================================================== */


#include <iostream.h>
#include <math.h>
#include <omp.h>
#include <stdlib.h>
#include <sys/time.h>


struct timeval start_time, stop_time;


#define MAX  100000000

int    num_threads;
int    start[100];
double x[MAX];
double min[100];






int main(int argc, char *argv[])
{
   char *s;
   int i;
   double my_min;
   int elapsed;

   /* -------------------------
      Generate random number
      ------------------------- */
   for (i = 0; i < MAX; i++)
      x[i] = random()/(double)1147483648;

   s = getenv("OMP_NUM_THREADS");

   if ( s == NULL )
   {
      cout << "Environment variable OMP_NUM_THREADS was not set" << endl;
      exit(1);
   }
   num_threads = atoi(s);

// num_threads = omp_get_num_threads(); // Does not work with OMP_NUM_THREADS

   cout << "Using " << num_threads << " threads..." << endl << endl;


   gettimeofday(&start_time, NULL);


   /* ******************************************************************* */
   #pragma omp parallel
   /* --------------------------------------
      Find the min. among my number

      The min is stored in min[s]
      -------------------------------------- */
   {
      int i, id;
      int n, start, stop;
      double my_min;

      n = MAX/omp_get_num_threads();   // Step size

      id = omp_get_thread_num();   // id is one of 0, 1, 2, ..., (num_threads-1)

      start = id;

      my_min = x[start];

      for (i = start+num_threads; i < MAX; i += num_threads )
      {
//       cout << i << endl;

         if ( x[i] < my_min )
            my_min = x[i];
      }
  
      min[id] = my_min;
   }
   /* ******************************************************************* */

   my_min = min[0];
   for (i = 1; i < num_threads; i++)
      if ( min[i] < my_min )
	 my_min = min[i];

   gettimeofday(&stop_time, NULL);

   elapsed = (stop_time.tv_sec*1000000 + stop_time.tv_usec) -
   		(start_time.tv_sec*1000000 + start_time.tv_usec);

   cout << "min = " << my_min << endl << endl; 
   cout << "Elapsed time = " << elapsed << " microseconds" << endl;
}