59 lines
1.3 KiB
C++
59 lines
1.3 KiB
C++
#include <iostream>
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#include <thread>
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#include <atomic>
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#include <sys/time.h>
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#include <ctime>
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#include <cmath>
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#include <random>
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static const int num_threads = 8;
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static const int max_ = 100000;
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void slice_of_pi(int tries, int my_id, std::atomic<int> & in_circle) {
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struct timeval tv;
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gettimeofday(&tv, NULL);
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srand(tv.tv_usec + my_id);
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std::uniform_int_distribution<int> distribution {0, max_};
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std::mt19937 engine; // Mersenne twister MT19937
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auto generator = std::bind(distribution, engine);
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double x, y, d;
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int _in_circle = 0;
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for(int i = 0; i < tries; i++) {
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x = (float)generator() / (float)max_;
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y = (float)generator() / (float)max_;
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d = sqrt(x * x + y * y);
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if(d < 1.0)
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_in_circle++;
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}
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in_circle += _in_circle;
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}
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int main(int argc, char * argv[]) {
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if(argc != 2) {
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std::cerr << "pi <number of attempts>" << std::endl;
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return 1;
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}
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std::atomic<int> successes {0};
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int attempts = atoi(argv[1]);
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std::thread t[num_threads];
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for (int i = 0; i < num_threads; ++i) {
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t[i] = std::thread(slice_of_pi, attempts, i, std::ref(successes));
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}
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for (int i = 0; i < num_threads; ++i) {
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t[i].join();
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}
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float pi = 4 * float(successes) / float(attempts * num_threads);
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printf("%0.8f\n", pi);
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return 0;
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}
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