fib test

#include <iostream> // cout
#include <cmath> // sqrt
#include <chrono>    // steady_clock
#include <sstream>   // istringstream

std::pair<int64_t, double> fib1(int64_t n) {
    auto t1 = std::chrono::steady_clock::now();

    int64_t nth_fib =    (1 / std::sqrt(5)) *
                        std::pow((1 + std::sqrt(5)) / 2, n) -
                        (1 / std::sqrt(5)) *
                        std::pow((1 - std::sqrt(5)) / 2, n);

    auto t2 = std::chrono::steady_clock::now();

    double seconds = std::chrono::duration_cast<std::chrono::duration<double>>(t2 - t1).count();

    return {nth_fib, seconds};
}

std::pair<int64_t, double> fib2(int64_t n) {
    auto t1 = std::chrono::steady_clock::now();

    int64_t a = 0, b = 1, c = 1;

    for(int64_t i = 1; i < n; i++) {
        c = a + b;
        a = b;
        b = c;
    }

    auto t2 = std::chrono::steady_clock::now();

    double seconds = std::chrono::duration_cast<std::chrono::duration<double>>(t2 - t1).count();

    return {c, seconds};
}

int main(int argc, const char * argv[]) {
    if(argc == 1) {
        std::cout << "Please specify a valid number to test." << "\n";

        return 1;
    }

    int64_t n;
    if (!(std::istringstream(argv[1]) >> n)) {
        std::cout << "Please specify a valid number to test." << "\n";
        return 1;
    }

    int64_t nth_fib1, nth_fib2;
    double seconds1, seconds2;

    std::tie(nth_fib1, seconds1) = fib1(n);
    std::tie(nth_fib2, seconds2) = fib2(n);

    std::cout << std::fixed << "Method 1: " << nth_fib1 << ", took " << seconds1 << "s\n";
    std::cout << std::fixed << "Method 2: " << nth_fib2 << ", took " << seconds2 << "s\n";

    return 0;
}