timing of std::pow, sqrt, cbrt.

pow_test.cpp

#include <algorithm>
#include <chrono>
#include <cmath>
#include <functional>
#include <iostream>
#include <random>
#include <vector>

using namespace std::placeholders;

static std::size_t const array_size = 1000000;
using array = std::array<double, array_size>;

array
random_array()
{
    std::random_device rd;
    std::default_random_engine e(rd());
    std::uniform_real_distribution<double> uniform_rnd(0, 1);

    array a;
    std::generate(a.begin(), a.end(), std::bind(uniform_rnd, e));
    return a;
}

template <typename F>
void
time(F&& f, std::string const info)
{
    std::chrono::time_point<std::chrono::system_clock> start, end;

    start = std::chrono::system_clock::now();
    f();
    end = std::chrono::system_clock::now();
 
    std::chrono::duration<double> elapsed_seconds = end-start;
 
    std::cout << info << " : " << elapsed_seconds.count() << "s\n";
}

int main()
{
    array a = random_array();

    time([&a]()
        {
            std::for_each(a.cbegin(), a.cend(),
                std::bind(std::pow<double, int>, _1, 2));
        },
        "^2 std::pow<double, int>"
        );

    time([&a]()
        {
            std::for_each(a.cbegin(), a.cend(),
                std::bind(std::pow<double, double>, _1, 2));
        },
        "^2 std::pow<double, double>"
        );

    time([&a]()
        {
            std::for_each(a.cbegin(), a.cend(),
                [](double const x) { return x*x; });
        },
        "^2 x*x"
        );

    time([&a]()
        {
            std::for_each(a.cbegin(), a.cend(),
                std::bind(std::pow<double, double>, _1, 0.5));
        },
        "sqrt std::pow<double, double>"
        );

    time([&a]()
        {
            std::for_each(a.cbegin(), a.cend(),
                sqrt);
        },
        "sqrt std::sqrt<double>"
        );

    time([&a]()
        {
            std::for_each(a.cbegin(), a.cend(),
                std::bind(std::pow<double, double>, _1, 1./3));
        },
        "cbrt std::pow<double, double>"
        );

    time([&a]()
        {
            std::for_each(a.cbegin(), a.cend(),
                cbrt);
        },
        "cbrt std::cbrt<double>"
        );
    return EXIT_SUCCESS;
}