c++ - Is this the fastest way and a new way to test special prime numbers? -


sample code:

bool is_special_prime (int n) {   qhash<int, int> o;   struct a_functor   {     int operator()(unsigned int n) { return n >> __builtin_ctz(n);}   }a;   int k = a(n + 1);   if(k == 1)     return 0;   o[k] = k;   int t = (n - 5) >> 1;   for(int = 0; < t; i++) {       k = a(n + k);       if(k == 1 || o.contains(k))         return 0;       o[k] = k;   }   return 1; }

is way can test numbers greater latest largest prime 2 ^ 57885161 − 1?

have read lucas-lehmer? sounds have bit more study before you're finding new , faster ways test primes. try implementing lucas-lehmer bignum library first.

your algorithm iterates n/2, far being quick, it's in fact extremely slow indeed (much slower prime seive). never find prime bigger 2^32 or 2^64, quite bit less 2^57885161. see why it's slow? can't return 1 until it's looped on value of less n/2.

i haven't checked whether code accurately determines primes or not.


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