src/libs/libgroff/prime.cc

   1 #include <math.h>
   2
   3 int is_prime(unsigned n)
   4 {
   5   if (n <= 3)
   6     return 1;
   7   if (!(n & 1))
   8     return 0;
   9   if (n % 3 == 0)
  10     return 0;
  11   unsigned lim = unsigned(sqrt((double)n));
  12   unsigned d = 5;
  13   for (;;) {
  14     if (d > lim)
  15       break;
  16     if (n % d == 0)
  17       return 0;
  18     d += 2;
  19     if (d > lim)
  20       break;
  21     if (n % d == 0)
  22       return 0;
  23     d += 4;
  24   }
  25   return 1;
  26 }