cpp benchmark

main.cpp

#include <chrono>
#include <iostream>
#include <random>

double dot(const std::vector<double> &x, const std::vector<double> &y)
{
    auto n = x.size();
    double s = 0.0;
    for (size_t i = 0; i < n; i++)
    {
        s += x[i] * y[i];
    }
    return s;
}

std::uniform_real_distribution<> dist(0.0, 1.0);

template <class URBG>
std::vector<double> uniform_rand(size_t n, URBG &engine)
{

    std::vector<double> v(n);
    for (size_t i = 0; i < n; i++)
    {
        v[i] = dist(engine);
    }
    return v;
}

int main()
{
    std::random_device seed_gen;
    std::default_random_engine engine(0);

    double s = 0.0;
    auto start = std::chrono::system_clock::now();
    for (size_t i = 0; i < 10000; i++)
    {
        auto x = uniform_rand(10000, engine);
        auto y = uniform_rand(10000, engine);
        s += dot(x, y);
    }
    auto end = std::chrono::system_clock::now();
    double elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count() / 1000.0;

    std::cout << "s = " << s << std::endl;
    std::cout << "elapsed = " << elapsed << "[sec]" << std::endl;
}

main2.cpp

#include <chrono>
#include <iostream>
#include <vector>

int main()
{
    double s = 0.0;
    auto start = std::chrono::system_clock::now();
    for (size_t i = 0; i < 5000; i++)
    {
        std::vector<double> v(1000000);
        v[0] = 10;
    }
    auto end = std::chrono::system_clock::now();
    double elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count() / 1000.0;

    std::cout << "elapsed = " << elapsed << "[sec]" << std::endl;
}