#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include "omp.h"
#include "aux.h"

int sequential_reduction(int *x, int n);
int parallel_reduction(int *x, int n);

int main(int argc, char **argv)
{
  int n, i, result;
  long t_start, t_end;
  int *x;

  // Command line argument: array length
  if (argc == 2)
  {
    n = atoi(argv[1]); /* the length of the pref */
  }
  else
  {
    printf("Usage:\n\n ./main n\n\nwhere n is the length of the array to be used.\n");
    return 1;
  }

  x = (int *)malloc(sizeof(int) * n);

  /* Fill the array with random numbers */
  srand(1);
  for (i = 0; i < n; i++)
    x[i] = rand() % n;

  /* Sequential reduction */
  t_start = usecs();
  result = sequential_reduction(x, n);
  t_end = usecs();
  printf("Sequential time : %8.2f msec.  ---  Result: %d\n", ((double)t_end - t_start) / 1000.0, result);

  /* Fill the array with random numbers */
  srand(1);
  for (i = 0; i < n; i++)
    x[i] = rand() % n;

  /* Parallel reduction */
  t_start = usecs();
  result = parallel_reduction(x, n);
  t_end = usecs();
  printf("Parallel   time : %8.2f msec.  ---  Result: %d\n", ((double)t_end - t_start) / 1000.0, result);

  return 0;
}

int sequential_reduction(int *x, int n)
{
  int i;

  for (i = 1; i < n; i++)
    operator(x, x + i);

  return x[0];
}

int parallel_reduction(int *x, int n)
{
  int i;
  int red = 0;

#pragma omp parallel

#pragma omp for reduction(+ : red)
  for (i = 0; i < n; i++)
  {
    operator(&red, x + i);
  }

  return red;
}