/* File:     omp_loop_sum_fail.c
 * Purpose:  Illustrate OpenMP rejection of a loop without "canonical shape"
 *
 * Compile:  gcc -g -Wall -fopenmp -o omp_loop_sum_fail omp_loop_sum_fail.c
 * Run:      Won't compile
 */
#include <stdio.h>
#include <stdlib.h>
#include <omp.h>

#define MAX 100000 

int thread_count;

int f(int i);
long long Loop_sum(int A[], int n);

int main(int argc, char* argv[]) {
   int i, n;
   int* A;
   long long sum;

   if (argc != 2) {
      fprintf(stderr, "usage: %s <number of threads>\n", argv[0]);
      exit(0);
   }
   thread_count = strtol(argv[1], NULL, 10);
   printf("How many elements?\n");
   scanf("%d", &n);
   A = malloc(n*sizeof(int));

   srandom(1);
   for (i = 0; i < n; i++)
      A[i] = random() % MAX;

   sum = Loop_sum(A, n);
   printf("loop sum = %lld\n", sum);

   return 0;
}  /* main */

long long Loop_sum(int A[], int n) {
   int i;
   long long sum = 0;
   int my_rank;

   /* This is going to cause a compile-time error */
#  pragma omp parallel for num_threads(thread_count) \
      reduction(+: sum) default(none) private(i, my_rank) \
      shared(n, A)
   for (i = 0; i < n; i = f(i)) {
      my_rank = omp_get_thread_num();
      printf("Thread %d > i = %d\n", my_rank, i);
      sum += A[i];
   }
   return sum;
}  /* Loop_sum */

int f(int i) {
   return i + 1;
}  /* f */