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  1.  
  2. #include <iostream>
  3. #include <chrono>
  4. #include <vector>
  5. #include <array>
  6.  
  7.  
  8. //Force 1-byte alignment
  9. #pragma pack(push, 1)
  10. struct UnalignedData {
  11. 	char c;
  12. 	double d;
  13. 	int i;
  14. };
  15. #pragma pack(pop)
  16.  
  17.  
  18. //aligned and padded by compiler
  19. struct AlignedData {
  20. 	double d;
  21. 	int i;
  22. 	char c;
  23. };
  24.  
  25.  
  26. void performance_test(){
  27. 	const int iterations = static_cast<int>(1e4);
  28. 	std::vector<UnalignedData> unaligned(iterations) ;
  29. 	std::vector<AlignedData> aligned(iterations);
  30.     std::array<double, iterations> collect;
  31.  
  32.     //initial
  33.     for(int i = 0; i < iterations; ++i){
  34.         unaligned[i] = {static_cast<char>(i), i * 3.14, i};
  35.         aligned[i] = {i * 3.14, i, static_cast<char>(i)};
  36.     }
  37.  
  38. 	//unaligned
  39. 	auto start = std::chrono::high_resolution_clock::now();
  40.  
  41. 	for(int i = 0; i < iterations; ++i){
  42. 		collect[i] = unaligned[i].d;
  43. 	}
  44.  
  45. 	auto end = std::chrono::high_resolution_clock::now();
  46. 	std::chrono::duration<double, std::milli> unaligned_time(end - start);
  47.  
  48.  
  49. 	//aligned
  50. 	start = std::chrono::high_resolution_clock::now();
  51. 	for(int i = 0; i < iterations; ++i){
  52. 		collect[i] = aligned[i].d;
  53. 	}
  54. 	end = std::chrono::high_resolution_clock::now();
  55. 	std::chrono::duration<double, std::milli> aligned_time(end - start);
  56.  
  57.  
  58. 	std::cout << "Exec Time of Unaligned: " << unaligned_time.count() << "ms" << std::endl;
  59. 	std::cout << "Exec Time of Aligned: " << aligned_time.count() << "ms" << std::endl;
  60. 	std::cout << "Performance Improvement: " << (unaligned_time.count() / aligned_time.count() -1)*100 << "%" << std::endl;
  61.  
  62.  
  63. }
  64.  
  65.  
  66. int main(){
  67.  
  68. 	performance_test();
  69. 	return 0;
  70. }
  71.  
Success #stdin #stdout 0.01s 5288KB
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Standard input is empty
stdout
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Exec Time of Unaligned: 0.000185ms
Exec Time of Aligned: 7.2e-05ms
Performance Improvement: 156.944%
https://ideone.com/KmWNUo
language:
C++14 (gcc 8.3)
created:
9 days ago
visibility:
public

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