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

#if RAND_MAX < 65536
static const size_t XRAND_MAX = (RAND_MAX + 1) * (RAND_MAX + 1) - 1;
static size_t xrand()
{
    return rand() * (RAND_MAX + 1) + rand();
}
// rand() is already ok; no need to do anything.
#else
static const size_t XRAND_MAX = RAND_MAX;
static size_t xrand()
{
    return rand();
}
#endif

size_t rand(size_t min_inclusive, size_t max_exclusive)
{
    const size_t range = (max_exclusive - min_inclusive);
    // huge interval or min >= max
    if (range == 0 || range > XRAND_MAX)
    {
        std::cout << "x < ERR::INVALID_PARAM" << std::endl;
        return 0;
    }

    const size_t inv_range = XRAND_MAX / range;

    // generate random number in [0, range)
    // idea: avoid skewed distributions when <range> doesn't evenly divide
    // XRAND_MAX by simply discarding values in the "remainder".
    // not expected to run often since XRAND_MAX is large.
    size_t x;
    do
    {
        x = xrand();
    } while (x >= range * inv_range);
    x /= inv_range;

    x += min_inclusive;
    //    if (x < max_exclusive)
    //    std::cout << "x < max_exclusive" << std::endl;
    return x;
}

static float RandFloat(float min, float max)
{
    return rand(min * 100.f, max * 100.f) / 100.f;
}

static float RandFloat(std::mt19937 &rng, float min, float max)
{
    return std::uniform_real_distribution<float>(min, max)(rng);
}

int main()
{

    int samples = 1000000;

    auto begin = std::chrono::high_resolution_clock::now();
    float value;

    for (int i = 0; i < samples; ++i)
    {
        value = RandFloat(0.f, 1.f);
    }
    auto end = std::chrono::high_resolution_clock::now();
    std::cout << "RandFloat(float min, float max): " << value;
    std::cout << "RandFloat(float min, float max): " << std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin).count() << "ns" << std::endl;

    begin = std::chrono::high_resolution_clock::now();
    for (int i = 0; i < samples; ++i)
    {
        std::mt19937 rng;
        rng.seed(i);
        value = RandFloat(rng, 0.f, 1.f);
    }
    end = std::chrono::high_resolution_clock::now();
    std::cout << "RandFloat(std::mt19937& rng, float min, float max) time: " << value;
    std::cout << "RandFloat(std::mt19937& rng, float min, float max) time: " << std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin).count() << "ns" << std::endl;

    return 0;
}