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  1. #include <iostream>
  2. #include <time.h>
  3.  
  4. using namespace std;
  5.  
  6. __attribute__ ((noinline)) int f(int x) {
  7. 	return x;
  8. }
  9. __attribute__ ((noinline)) int g(const int& x) {
  10. 	return x;
  11. }
  12.  
  13. const unsigned N = 200000000;
  14.  
  15. int main() {
  16. 	clock_t start, end, loop_time;
  17. 	unsigned throwaway = 0;
  18.  
  19.  	start = clock();
  20. 	for (unsigned i = 0; i < N; ++i) {
  21. 		throwaway += i;
  22. 	}
  23.  	end = clock();
  24. 	cout << "Loop time: " << (end - start) << " ticks" << endl;
  25.  
  26.  	start = clock();
  27. 	for (unsigned i = 0; i < N; ++i) {
  28. 		throwaway += f(i);
  29. 		throwaway -= i;
  30. 	}
  31.  	end = clock();
  32. 	cout << "By value: " << (end - start) << " ticks" << endl;
  33.  
  34.  	start = clock();
  35. 	for (unsigned i = 0; i < N; ++i) {
  36. 		throwaway += g(i);
  37. 		throwaway -= i;
  38. 	}
  39.  	end = clock();
  40. 	cout << "By ref: " << (end - start) << " ticks" << endl;
  41.  
  42. 	cout << "Throwaway (to stop optimisation) = " << throwaway << endl;
  43. 	return 0;
  44. }
Success #stdin #stdout 1.55s 2680KB
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Standard input is empty
stdout
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Loop time: 190000 ticks
By value: 540000 ticks
By ref: 810000 ticks
Throwaway (to stop optimisation) = 3649838848
https://ideone.com/Wihzi
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
public

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