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  1. #include <iostream>
  2. #include <random>
  3. #include <chrono>
  4. #include <algorithm>
  5. using namespace std;
  6. using namespace std::chrono; 
  7.  
  8. const int sz = 500000; 
  9. const int rpt = 2000;
  10. int n; 
  11. double sum=0;
  12.  
  13. void f1(double *arr) {
  14.   for (int i = 0; i < n; i++)
  15.     sum += arr[i];
  16. }
  17.  
  18. void f2(double *arr) {
  19.   for (int i = 0; i < n; i++)
  20.     if (arr[i])
  21.         sum += arr[i];
  22. }
  23.  
  24. int main() {
  25. 	mt19937_64 engine(time(0));
  26. 	uniform_real_distribution<> distri(-1000000.0, +1000000.0);
  27. 	uniform_int_distribution<int> distn(0,sz-1);
  28. 	volatile double d; 
  29.  
  30. 	n = sz;
  31. 	double *arr = new double[n]; 
  32. 	for (int i=0; i<sz/2; i++) {   // play with density here
  33. 		int k = distn(engine);
  34. 		arr[k]=distri(engine);  
  35. 	}
  36. 	int zero = count(arr, arr+n, 0.0);
  37. 	cout << zero << " null items, " << (double)zero/sz*100.0 << "%"<<endl;  
  38.  
  39. 	high_resolution_clock::time_point t1=high_resolution_clock::now(); 
  40. 	for (int j=0; j<rpt; j++) {
  41.   	  sum=0; 
  42. 	  f1(arr);
  43. 	  d=sum;
  44. 	}
  45. 	high_resolution_clock::time_point t2=high_resolution_clock::now(); 
  46. 	cout << duration_cast<milliseconds>(t2-t1).count() <<endl; 
  47. 	cout<<"\t"<<sum<<endl; 
  48.  
  49. 	high_resolution_clock::time_point t3=high_resolution_clock::now(); 
  50. 	for (int j=0; j<rpt; j++) {
  51. 	  sum=0;
  52.  	  f2(arr);
  53.  	  d=sum;
  54. 	}
  55. 	high_resolution_clock::time_point t4=high_resolution_clock::now(); 
  56. 	cout << duration_cast<milliseconds>(t4-t3).count() <<endl; 
  57. 	cout<<"\t"<<sum<<endl; 
  58.  
  59. 	return 0;
  60. }
Success #stdin #stdout 4.42s 19144KB
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stdin
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Standard input is empty
stdout
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303083 null items, 60.6166%
797
	3.88259e+08
3692
	3.88259e+08
https://ideone.com/6DXdVH
language:
C++14 (gcc 8.3)
created:
6 years ago
visibility:
public

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