cpp-coding-exercise/pi-monte-carlo/main.cpp at main · DoctorLai/cpp-coding-exercise · GitHub

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#include <algorithm>

#include <cstdint>

#include <iostream>

#include <numeric>

#include <random>

#include <thread>

#include <vector>

static std::uint64_t

count_hits(std::uint64_t n, std::uint64_t seed)

{

std::mt19937_64 rng(seed);

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

std::uint64_t hits = 0;

for (std::uint64_t i = 0; i < n; ++i) {

const double x = dist(rng);

const double y = dist(rng);

if (x * x + y * y <= 1.0)

++hits;

}

return hits;

}

int

main(int argc, char* argv[])

{

int threads = 2;

std::uint64_t n = 1'000'000;

if (argc > 1)

threads = std::max(1, std::atoi(argv[1]));

if (argc > 2)

n = std::max<std::uint64_t>(1, std::strtoull(argv[2], nullptr, 10));

const std::uint64_t base = n / threads;

const std::uint64_t rem = n % threads;

std::vector<std::thread> pool;

std::vector<std::uint64_t> hits(threads, 0);

// a single nondeterministic seed source; each thread gets a different seed

std::random_device rd;

const std::uint64_t master_seed = (static_cast<std::uint64_t>(rd()) << 32) ^ static_cast<std::uint64_t>(rd());

for (int i = 0; i < threads; ++i) {

const std::uint64_t points = base + (static_cast<std::uint64_t>(i) < rem ? 1 : 0);

const std::uint64_t seed = master_seed + 0x9e3779b97f4a7c15ULL * static_cast<std::uint64_t>(i + 1);

pool.emplace_back([&, i, points, seed] { hits[i] = count_hits(points, seed); });

}

for (auto& t : pool)

t.join();

const std::uint64_t total_hits = std::accumulate(hits.begin(), hits.end(), std::uint64_t{0});

const long double pi = 4.0 * static_cast<long double>(total_hits) / static_cast<long double>(n);

std::cout << pi << "\n";

return 0;

}

cpp-coding-exercise/pi-monte-carlo/main.cpp at main · DoctorLai/cpp-coding-exercise · GitHub

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