Precomputed factorial

factorial.cpp

#include <numeric>


template<class T>
constexpr T cfact(unsigned f) {
	return f?cfact<T>(f - 1)*f : 1;
}

template<class T>
constexpr T factorial_max_helper(T value_so_far, unsigned f) {
	return std::numeric_limits<T>::max() / value_so_far < f ? f - 1 : factorial_max_helper(value_so_far*f, f + 1);
}

template<class T,size_t... Indices>
T factorial_helper(unsigned f, std::index_sequence<Indices...>) {
	static constexpr T ar[] = { cfact<T>(Indices)... };
	return ar[f];
}

template<class T>
T factorial(unsigned f) {
	return factorial_helper<T>(f, std::make_index_sequence<factorial_max_helper<T>(1, 1) + 1>{});
}

#include <iostream>
int main() {

	unsigned i = 7;
	volatile auto r = factorial<int>(i);
	std::cout << r << "\n";
}