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  1. #include <iostream>
  2. #include <random>
  3. #include <chrono>
  4. using namespace std::chrono;
  5.  
  6. int main()
  7. {
  8.     // variables
  9. 	size_t start_time = 0, end_time = 0, for_time = 0; // speed record
  10. 	unsigned int N = 100000;
  11. 	double *a = new double [N]; // array of random numbers
  12. 	unsigned int i=0;
  13. 	std::normal_distribution<double> dist(0,1); // N(0,1) distribution
  14.  
  15. 	printf("1.Test duration_cast<precision>(duration_object).count() method:\n");
  16. 	size_t t64 = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  17. 	printf("  time now in dec ns: %u (uint64, directly obtained)\n", t64);
  18. 	printf("           in hex   : %16llx\n\n", t64);
  19.  
  20.     printf("2.make sure uint64 -> uint32 discards higher bits(suitable for seeding):\n");
  21. 	unsigned long t32 = static_cast<unsigned long>(t64);
  22. 	printf("  time now in hex ns: %16x (truncated to uint32)\n\n", t32);
  23.  
  24. 	printf("3.generating %u N(0,1) random numbers using different engines...\n", N);
  25.  
  26. 	// Time cost of for-loop body
  27. 	start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  28. 	for(i=0; i<N; i++){}
  29. 	end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  30. 	for_time = end_time - start_time;
  31. 	printf("%16u ns used on for-loop body\n", for_time);
  32.  
  33. 	// mt19937 engine
  34. 	start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  35. 	std::mt19937 mt(static_cast<unsigned long>(duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count()));
  36. 	for(i=0; i<N; i++)
  37. 		a[i] = dist(mt);
  38. 	end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  39. 	printf("%16u ns for mt19937\n", (end_time-start_time-for_time)) ;
  40.  
  41. 	// mt19937_64 engine
  42. 	start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  43. 	std::mt19937_64 mt64(static_cast<unsigned long>(duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count()));
  44. 	for(i=0; i<N; i++)
  45. 		a[i] = dist(mt64);
  46. 	end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  47. 	printf("%16u ns for mt19937_64\n", (end_time-start_time-for_time)) ;
  48.  
  49. 	// minstd_rand engine
  50. 	start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  51. 	std::minstd_rand  min_rnd(static_cast<unsigned long>(duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count()));
  52. 	for(i=0; i<N; i++)
  53. 		a[i] = dist(min_rnd);
  54. 	end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  55. 	printf("%16u ns for minstd_rand\n", (end_time-start_time-for_time)) ;
  56.  
  57. 	// default_random_engine
  58. 	start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  59. 	std::default_random_engine def_rnd(static_cast<unsigned long>(duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count()));
  60. 	for(i=0; i<N; i++)
  61. 		a[i] = dist(def_rnd);
  62. 	end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  63. 	printf("%16u ns for default_random_engine\n", (end_time-start_time-for_time)) ;
  64.  
  65. 	// random_device (hardware generator)
  66. 	start_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  67. 	std::random_device rd;
  68. 	for(i=0; i<N; i++)
  69. 		a[i] = dist(rd);
  70. 	end_time = duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
  71. 	printf("%16u ns for random_device\n", (end_time-start_time-for_time)) ;
  72.  
  73. 	delete [] a;
  74. 	system("PAUSE");
  75. 	return 0;
  76. }
Success #stdin #stdout #stderr 0.36s 3036KB
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stdin
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Standard input is empty
stdout
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1.Test duration_cast<precision>(duration_object).count() method:
  time now in dec ns: 1292916176 (uint64, directly obtained)
           in hex   :         4d1055d0

2.make sure uint64 -> uint32 discards higher bits(suitable for seeding):
  time now in hex ns:         4d1055d0 (truncated to uint32)

3.generating 100000 N(0,1) random numbers using different engines...
               0 ns used on for-loop body
        14502000 ns for mt19937
        12965000 ns for mt19937_64
        13066000 ns for minstd_rand
        12821000 ns for default_random_engine
       317918000 ns for random_device
stderr
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sh: PAUSE: not found
https://ideone.com/u20Wu0
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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