1 files changed, 55 insertions, 0 deletions
diff --git a/src/libs/libgroff/prime.cpp b/src/libs/libgroff/prime.cpp
new file mode 100644
index 0000000..5ae068d
--- /dev/null
+++ b/src/libs/libgroff/prime.cpp
@@ -0,0 +1,55 @@
+/* Copyright (C) 2014-2020 Free Software Foundation, Inc.
+
+This file is part of groff.
+
+groff is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation, either version 2 of the License, or
+(at your option) any later version.
+
+groff is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+The GNU General Public License version 2 (GPL2) is available in the
+internet at <http://www.gnu.org/licenses/gpl-2.0.txt>. */
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <assert.h>
+#include <math.h>
+
+bool is_prime(unsigned n)
+{
+  assert(n > 1);
+  if (n <= 3)
+    return true;
+  if (!(n & 1))
+    return false;
+  if (n % 3 == 0)
+    return false;
+  unsigned lim = unsigned(sqrt((double)n));
+  unsigned d = 5;
+  for (;;) {
+    if (d > lim)
+      break;
+    if (n % d == 0)
+      return false;
+    d += 2;
+    if (d > lim)
+      break;
+    if (n % d == 0)
+      return false;
+    d += 4;
+  }
+  return true;
+}
+
+// Local Variables:
+// fill-column: 72
+// mode: C++
+// End:
+// vim: set cindent noexpandtab shiftwidth=2 textwidth=72: