That 123456 again

And why GMP C++ interface is so slow...

	#include <iostream>
	#include <ctime>
	#include <gmpxx.h>
	typedef mpz_class Integer;
	Integer N[] = {1, 12, 123, 1234, 12345, 123456};
	Integer sum_digits(Integer n);
	Integer factorial(Integer n);
	int main(int argc, char *argv[])
	{
	Integer res = 0;
	std::clock_t start = std::clock();
	for(int i = 0; i < sizeof(N)/sizeof(Integer); ++i)
	{
	res += sum_digits(factorial(N[i]));
	}
	std::cout << res << std::endl;
	std::clock_t end = std::clock();
	std::cout << "Execution time: "
	<< 1e3 * ((double) (end - start)) / CLOCKS_PER_SEC
	<< " ms" << std::endl;
	}
	Integer factorial(Integer n)
	{
	Integer res = 1;
	for(Integer k = n; k > 1; k -= 1)
	res *= k;
	return res;
	}
	Integer sum_digits(Integer n)
	{
	Integer res = 0;
	std::string s = n.get_str();
	for(auto i = s.begin(); i != s.end(); ++i)
	res += (int) *i - (int) '0';
	return res;
	}

view raw gmpxx_test.cxx hosted with ❤ by GitHub

	alexey at daphne in tests$ clang++ gmp_test.cxx -lgmp -lgmpxx -std=c++11 -O3
	alexey at daphne in tests$ ./a.out
	2652733
	Execution time: 8394.96 ms
	alexey at daphne in tests$

view raw gistfile1.sh hosted with ❤ by GitHub

Even slower than Lisp. Or it's C++ itself?