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  1. #include <time.h>
  2.  
  3. #include <atomic>
  4. #include <mutex>
  5.  
  6. static std::atomic<bool> single_threaded(true);
  7.  
  8. int main(int argc, char *argv[])
  9. {
  10. 	(void)argv;
  11. 	if (argc == 100001) { single_threaded = !single_threaded; /* to prevent compiler optimization later */ }
  12. 	int n = argc == 100000 ? -1 : 10000000;
  13. 	{
  14. 		std::mutex mutex;
  15. 		clock_t const begin = clock();
  16. 		unsigned int total = 0;
  17. 		for (int i = 0; i < n; ++i)
  18. 		{
  19. 			if (single_threaded)
  20. 			{
  21. 				total = ((total << 1) ^ i) + ((total >> 1) & i);
  22. 			}
  23. 			else
  24. 			{
  25. 				std::lock_guard<std::mutex> lock(mutex);
  26. 				total = ((total << 1) ^ i) + ((total >> 1) & i);
  27. 			}
  28. 		}
  29. 		clock_t const end = clock();
  30. 		printf("Conditional: %u ms, total = %u\n", (unsigned int)((end - begin) * 1000U / CLOCKS_PER_SEC), total);
  31. 	}
  32. 	{
  33. 		std::mutex mutex;
  34. 		clock_t const begin = clock();
  35. 		unsigned int total = 0;
  36. 		for (int i = 0; i < n; ++i)
  37. 		{
  38. 			std::lock_guard<std::mutex> lock(mutex);
  39. 			total = ((total << 1) ^ i) + ((total >> 1) & i);
  40. 		}
  41. 		clock_t const end = clock();
  42. 		printf("Unconditional: %u ms, total = %u\n", (unsigned int)((end - begin) * 1000U / CLOCKS_PER_SEC), total);
  43. 	}
  44. }
Success #stdin #stdout 0.34s 3456KB
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Standard input is empty
stdout
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Conditional: 27 ms, total = 3684292139
Unconditional: 311 ms, total = 3684292139
https://ideone.com/fmrVFj
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
secret

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