#include <iostream>
#include <chrono>

using namespace std;
using namespace std::chrono;

template<long long I, long long J>
struct midpt {
	static const long long value = I+(J-I)/2;
	// alternative method of associating a constant value:
	//enum {value = I+(J-I)/2};
};

template<long long X, long long I, long long J, typename Cond=void>
struct isprimehelper {
	static const bool value = 
		isprimehelper<X,I+1,midpt<I,J>::value>::value
	      && isprimehelper<X,midpt<I,J>::value+1,J>::value;
};

template<long long X, long long I, long long J>
struct isprimehelper<X,I,J, typename enable_if<X%I==0>::type> {
	static const bool value = false;
};

template<long long X, long long I, long long J>
struct isprimehelper<X,I,J,typename enable_if<X%I!=0 && (I>=J||I>X/I)>::type> {
	static const bool value = true;
};

template<long long X>
struct isprime {
	static const bool value = isprimehelper<X,2,X-1>::value;
};

template<long long X, typename Cond=void>
struct nextprime {
	static const long long value = nextprime<X+1>::value;
};

template<long long X>
struct nextprime<X,typename enable_if<isprime<X>::value>::type> {
	static const long long value = X;
};

int main(int argc, char **argv) {
	cout << "starting program" << endl;
	// constexpr variable:
	//    must be constructed or assigned a value at declaration
	//    the assigned value or parameteres to the constructor must
	//        only be literals, constexpr variables, or constexpr fns
	//    if a constructor is used, it must be a constexpr constructor
	auto t1 = high_resolution_clock::now();
	long long largishprime = nextprime<1000000>::value;
	auto t2 = high_resolution_clock::now();
	cout << "time = " << duration_cast<microseconds>(t2-t1).count()
		<< " microseconds" << endl;
	cout << largishprime << endl;

	// (not possible for TMP)
	/*
	long long x;
	cin >> x;
	t1 = high_resolution_clock::now();
	x = nextprime(x);
	t2 = high_resolution_clock::now();
	cout << "time = " << duration_cast<microseconds>(t2-t1).count()
		<< " microseconds" << endl;
	cout << x << endl;
	*/
}