tasks a-s

Task/Parallel-calculations/C/parallel-calculations.c

@@ -0,0 +1,33 @@
+#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;
+}