fork download 
  1. /** @file
  2.  * @author  Chuan-Bin "Bill" Huang
  3.  * @date    2013-06-27
  4.  * @version 1.0
  5.  *  
  6.  * @brief   A Brief Demo of C++11 <chrono> and <random>
  7.  * @section References
  8.  * 
  9.  * Original BBS posts:
  10.  * 
  11.  * <a href="https://w...content-available-to-author-only...t.cc/bbs/C_and_CPP/M.1372284252.A.99D.html">C++11 random</a> 
  12.  * 
  13.  * <a href="https://w...content-available-to-author-only...t.cc/bbs/C_and_CPP/M.1372283467.A.A74.html">C++11 chrono</a>
  14.  * 
  15.  */
  16.  
  17.  #include <iostream>
  18.  #include <random>
  19.  #include <chrono>
  20.  using namespace std::chrono;
  21.  // (wrong) using namespace std::random; 
  22.  
  23.  int main()
  24.  {
  25.      // Experimental Parameters
  26.      size_t start_time = 0, end_time = 0, for_time = 0; // speed record
  27.      unsigned int N = 1000000;
  28.      double *a = new double [N]; // array of random numbers
  29.      unsigned int i=0;
  30.      std::normal_distribution<double> dist(0,1); // N(0,1) distribution
  31.  
  32.      // Format Conversion
  33.      printf("1.Test duration_cast<precision>(duration_object).count() method:\n");
  34.      size_t t64 = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  35.      printf("  time now in dec ns: %u (uint64, directly obtained)\n", t64);
  36.      printf("           in hex   : %16llx\n\n", t64);
  37.  
  38.      printf("2.make sure uint64 -> uint32 discards higher bits(suitable for seeding):\n");
  39.      unsigned long t32 = static_cast<unsigned long>(t64);
  40.      printf("  time now in hex ns: %16x (truncated to uint32)\n\n", t32);
  41.  
  42.      printf("3.generating %u N(0,1) random numbers using different engines...\n", N);
  43.  
  44.      // Time cost of for-loop body
  45.      start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  46.      for(i=0; i<N; i++){}
  47.      end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  48.      for_time = end_time - start_time;
  49.      printf("%16u ns used on for-loop body\n", for_time);
  50.  
  51.      // mt19937 engine
  52.      start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  53.      std::mt19937 mt(static_cast<unsigned long>(duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count()));
  54.      for(i=0; i<N; i++)
  55.          a[i] = dist(mt);
  56.      end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  57.      printf("%16u ns for mt19937\n", (end_time-start_time-for_time));
  58.  
  59.      // mt19937_64 engine
  60.      start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  61.      std::mt19937_64 mt64(static_cast<unsigned long>(duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count()));
  62.      for(i=0; i<N; i++)
  63.          a[i] = dist(mt64);
  64.      end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  65.      printf("%16u ns for mt19937_64\n", (end_time-start_time-for_time));
  66.  
  67.      // minstd_rand engine
  68.      start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  69.      std::minstd_rand  min_rnd(static_cast<unsigned long>(duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count()));
  70.      for(i=0; i<N; i++)
  71.          a[i] = dist(min_rnd);
  72.      end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  73.      printf("%16u ns for minstd_rand\n", (end_time-start_time-for_time));
  74.  
  75.      // default_random_engine
  76.      start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  77.      std::default_random_engine def_rnd(static_cast<unsigned long>(duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count()));
  78.      for(i=0; i<N; i++)
  79.          a[i] = dist(def_rnd);
  80.      end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  81.      printf("%16u ns for default_random_engine\n", (end_time-start_time-for_time));
  82.  
  83.      // random_device (hardware generator)
  84.      start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  85.      std::random_device rd;
  86.      for(i=0; i<N; i++)
  87.          a[i] = dist(rd);
  88.      end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  89.      printf("%16u ns for random_device\n", (end_time-start_time-for_time));
  90.  
  91.      delete [] a;
  92.      printf("\nProgram Ended! Press Enter to quit.");
  93.      std::cin.get();
  94.      return 0;
  95.  }
  96.  
Success #stdin #stdout 0.52s 16072KB
comments (?)
stdin 
Standard input is empty
stdout 
1.Test duration_cast<precision>(duration_object).count() method:
  time now in dec ns: 1251234941 (uint64, directly obtained)
           in hex   : 14e9e8b14a94547d

2.make sure uint64 -> uint32 discards higher bits(suitable for seeding):
  time now in hex ns:         4a94547d (truncated to uint32)

3.generating 1000000 N(0,1) random numbers using different engines...
             151 ns used on for-loop body
        42934807 ns for mt19937
        33733544 ns for mt19937_64
        33397393 ns for minstd_rand
        32978185 ns for default_random_engine
       380725676 ns for random_device

Program Ended! Press Enter to quit.
https://ideone.com/De11nm
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!