/* isPrime-fn2.h
 * efficient recognizer (predicate function) for prime numbers
 */

#include <cmath>           //for sqrt(), ceil()
using namespace std;

/* isPrime()---------------------------------------
 * returns true if n is prime; otherwise returns false
 */
bool isPrime(unsigned long n){
    unsigned long pd = 2,           //potential divisor
    limit = sqrt(n);                //upper bound for potential divisors
    int divisible = 0;              //boolean flag (0 is false, 1 is true)

    //check divisors up to limit
    do{
	divisible = (n % pd == 0);
        pd++;
    }while(!divisible && (pd <= limit));

    //return result
    //if(divisible)
    //return 0;
    //else
    // return 1;

    return (!divisible || n == 2);
}