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/* { dg-do run } */
/* { dg-options "-O2 -fopenmp" } */
/* { dg-require-effective-target tls_runtime } */
#include <omp.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int cnt;
#pragma omp threadprivate (cnt)
void
nqueens (char *a, int n, int pos)
{
/* b[i] = j means the queen in i-th row is in column j. */
char b[pos + 1];
int i, j;
memcpy (b, a, pos);
for (i = 0; i < n; i++)
{
for (j = 0; j < pos; j++)
if (b[j] == i || b[j] == i + pos - j || i == b[j] + pos - j)
break;
if (j < pos)
continue;
if (pos == n - 1)
/* Found a solution. Could output it here. */
++cnt;
else
{
b[pos] = i;
#pragma omp task
nqueens (b, n, pos + 1);
}
}
}
int
main (int argc, char **argv)
{
int n = 8;
if (argc >= 2)
n = strtoul (argv[1], NULL, 0);
if (n < 1 || n > 127)
{
fprintf (stderr, "invalid count %d\n", n);
return 1;
}
cnt = 0;
double stime = omp_get_wtime ();
nqueens ("", n, 0);
printf ("serial N %d solutions # %d time %f\n", n, cnt, omp_get_wtime () - stime);
#pragma omp parallel
cnt = 0;
stime = omp_get_wtime ();
int tempcnt = 0;
#pragma omp parallel reduction (+:tempcnt)
{
#pragma omp single
nqueens ("", n, 0);
tempcnt = cnt;
}
cnt = tempcnt;
printf ("parallel N %d solutions # %d time %f\n", n, cnt, omp_get_wtime () - stime);
return 0;
}
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