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