fib-openmp.c

/*
 * fib.cpp
 *
 * Time how long it takes to calculate a Fibonacci number. See
 * http://en.wikipedia.org/wiki/Fibonacci_number for information about the
 * Fibonacci sequence. This application demonstrates the use of the cilk_spawn
 * and cilk_sync keywords.
 *
 * This program takes a single parameter to specify the number of workers to
 * be used in the calculation. If not specified, Intel Cilk Plus will query
 * the operating system to determine the number of cores on the system and use
 * that many workers.
 */

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

int fib(int n)
{
  int x, y;
  if (n < 2)
    return n;
#pragma omp task shared(x)
  x =  fib(n-1);
#pragma omp task shared(y)  
  y = fib(n-2);
#pragma omp taskwait
  
  return x + y;
}

int main(int argc, char *argv[])
{
  // Fibonacci number to be calculated.  39 is big enough to take a
  // reasonable amount of time
  int n = 39;
  
  // If we've got a parameter, assume it's the number of workers to be used
  if (argc > 1)
    {
      // Values less than 1, or parameters that aren't numbers aren't allowed
      if (atoi(argv[1]) < 1)
        {
          printf("Usage: fib [workers]\n");
          return 1;
        }
      
      // Set the number of workers to be used
      omp_set_num_threads(atoi(argv[1]));
    }
  
  // Time how long it takes to calculate the nth Fibonacci number
  clock_t start = clock();
  int result = fib(n);
  clock_t end = clock();
  
  // Display our results
  double duration = (double)(end - start) / CLOCKS_PER_SEC;
  printf("Fibonacci number #%d is %d.\n", n, result);
  printf("Calculated in %.3f seconds using %d workers.\n",
         duration, omp_get_num_threads());
  
  return 0;
}