1 files changed, 28 insertions, 0 deletions
diff --git a/gnu/usr.bin/groff/libgroff/prime.cc b/gnu/usr.bin/groff/libgroff/prime.cc
new file mode 100644
index 000000000000..531856c2a59a
--- /dev/null
+++ b/gnu/usr.bin/groff/libgroff/prime.cc
@@ -0,0 +1,28 @@
+extern "C" {
+#include <math.h>
+}
+
+int is_prime(unsigned n)
+{
+  if (n <= 3)
+    return 1;
+  if (!(n & 1))
+    return 0;
+  if (n % 3 == 0)
+    return 0;
+  unsigned lim = unsigned(sqrt((double)n));
+  unsigned d = 5;
+  for (;;) {
+    if (d > lim)
+      break;
+    if (n % d == 0)
+      return 0;
+    d += 2;
+    if (d > lim)
+      break;
+    if (n % d == 0)
+      return 0;
+    d += 4;
+  }
+  return 1;
+}