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

int main()
{
        int data[] = {12757923, 12878611, 12878893, 12757923, 15808973, 15780709, 197622519};
        int largest, largest_factor = 0;

        omp_set_num_threads(4);
        /* "omp parallel for" turns the for loop multithreaded by making each thread
         * iterating only a part of the loop variable, in this case i; variables declared
         * as "shared" will be implicitly locked on access
         */
        #pragma omp parallel for shared(largest_factor, largest)
        for (int i = 0; i < 7; i++) {
                int p, n = data[i];

                for (p = 3; p * p <= n && n % p; p += 2);
                if (p * p > n) p = n;
                if (p > largest_factor) {
                        largest_factor = p;
                        largest = n;
                        printf("thread %d: found larger: %d of %d\n",
                                omp_get_thread_num(), p, n);
                } else {
                        printf("thread %d: not larger:   %d of %d\n",
                                omp_get_thread_num(), p, n);
                }
        }

        printf("Largest factor: %d of %d\n", largest_factor, largest);
        return 0;
}