main.cpp

#include <iostream>
#include <chrono>
#include <cmath>

int main(int argc, char *argv[])
{
    constexpr std::size_t CONSTEXPR_SIZE = 1000000000000000000;
    // The good way to use this program is to call it like so :
    // ./main 1000000000000000000
    std::size_t DYNAMIC_SIZE = std::atoll(argv[1]);

    // Ensure the values are the same
    // Compiler is smart, if you do this verification, he'll inline the last
    // computation
    // if (CONSTEXPR_SIZE != DYNAMIC_SIZE) {
    //     std::cerr << "Wrong size" << std::endl;
    //     return 1;
    // }

    // CONSTEXPR Loop
    // O(n^3) computation executed instantly
    std::size_t count = 0;
    auto before = std::chrono::high_resolution_clock::now();
    for (std::size_t i = 0; i < CONSTEXPR_SIZE; i++) {
        for (std::size_t j = 0; j < CONSTEXPR_SIZE; j++) {
            for (std::size_t k = 0; k < CONSTEXPR_SIZE; k++) {
                count++;
            }
        }
    }
    auto after = std::chrono::high_resolution_clock::now();

    // Print count so the compiler doesn't avoid the computation
    std::cout << count << std::endl;
    std::cout << (after - before).count() << std::endl;

    // DYNAMIC Loop
    // super long O(n) computation
    count = 0;
    before = std::chrono::high_resolution_clock::now();
    for (std::size_t i = 0; i < DYNAMIC_SIZE; i++) {
        count++;
    }
    after = std::chrono::high_resolution_clock::now();
    std::cout << count << std::endl;

    std::cout << (after - before).count() << std::endl;

    return 0;
}