libgomp/testsuite/libgomp.c/nqueens-1.c

   1 /* { dg-do run } */
   2 /* { dg-require-effective-target tls_runtime } */
   3
   4 #include <omp.h>
   5 #include <stdio.h>
   6 #include <string.h>
   7 #include <stdlib.h>
   8
   9 int cnt;
  10 #pragma omp threadprivate (cnt)
  11
  12 void
  13 nqueens (char *a, int n, int pos)
  14 {
  15   /* b[i] = j means the queen in i-th row is in column j.  */
  16   char b[pos + 1];
  17   int i, j;
  18   memcpy (b, a, pos);
  19   for (i = 0; i < n; i++)
  20     {
  21       for (j = 0; j < pos; j++)
  22         if (b[j] == i || b[j] == i + pos - j || i == b[j] + pos - j)
  23           break;
  24       if (j < pos)
  25         continue;
  26       if (pos == n - 1)
  27         /* Found a solution.  Could output it here.  */
  28         ++cnt;
  29       else
  30         {
  31           b[pos] = i;
  32           #pragma omp task
  33             nqueens (b, n, pos + 1);
  34         }
  35     }
  36 }
  37
  38 int
  39 main (int argc, char **argv)
  40 {
  41   int n = 8;
  42   if (argc >= 2)
  43     n = strtoul (argv[1], NULL, 0);
  44   if (n < 1 || n > 127)
  45     {
  46       fprintf (stderr, "invalid count %d\n", n);
  47       return 1;
  48     }
  49   cnt = 0;
  50   double stime = omp_get_wtime ();
  51   nqueens ("", n, 0);
  52   printf ("serial   N %d solutions # %d time %f\n", n, cnt, omp_get_wtime () - stime);
  53   #pragma omp parallel
  54     cnt = 0;
  55   stime = omp_get_wtime ();
  56   int tempcnt = 0;
  57   #pragma omp parallel reduction (+:tempcnt)
  58     {
  59       #pragma omp single
  60         nqueens ("", n, 0);
  61       tempcnt = cnt;
  62     }
  63   cnt = tempcnt;
  64   printf ("parallel N %d solutions # %d time %f\n", n, cnt, omp_get_wtime () - stime);
  65   return 0;
  66 }