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  1. #include <iostream>
  2. #include <chrono>
  3. #include <vector>
  4. #include <numeric>
  5.  
  6. using namespace std;
  7. using namespace std::chrono;
  8.  
  9.  
  10. #define N 10000000
  11. int main()
  12. {
  13.     //constexpr int N = 10000000;
  14.     vector<int> v(N);
  15.     for (int i = 0; i<N; ++i)
  16.         v[i] = i;
  17.  
  18.  
  19.  
  20.     //looping with iterators
  21.     {
  22.         high_resolution_clock::time_point t1 = high_resolution_clock::now();
  23.  
  24.         long long int sum = 0;
  25.         for (auto it = v.begin(); it != v.end(); ++it)
  26.             sum+=*it;
  27.  
  28.         high_resolution_clock::time_point t2 = high_resolution_clock::now();
  29.  
  30.         auto duration = std::chrono::duration_cast<std::chrono::microseconds>( t2 - t1 ).count();
  31.  
  32.         cout << duration << "microseconds  output = " << sum << " (Iterators)\n";
  33.     }
  34.  
  35.                 //using std::accumulate
  36.     {
  37.         high_resolution_clock::time_point t1 = high_resolution_clock::now();
  38. 		long long int start = 0;
  39.         long long int sum = accumulate(v.begin(), v.end(), start);
  40.  
  41.         high_resolution_clock::time_point t2 = high_resolution_clock::now();
  42.  
  43.         auto duration = std::chrono::duration_cast<std::chrono::microseconds>( t2 - t1 ).count();
  44.  
  45.         cout << duration << "microseconds  output = " << sum << " (std::accumulate)\n";
  46.     }
  47.  
  48.     //looping with integers
  49.     {
  50.         high_resolution_clock::time_point t1 = high_resolution_clock::now();
  51.  
  52.         long long int sum = 0;
  53.         for (int i = 0; i<N; ++i)
  54.             sum+=v[i];
  55.  
  56.         high_resolution_clock::time_point t2 = high_resolution_clock::now();
  57.  
  58.         auto duration = std::chrono::duration_cast<std::chrono::microseconds>( t2 - t1 ).count();
  59.  
  60.         cout << duration << "microseconds  output = " << sum << " (integer index)\n";
  61.     }
  62.  
  63.     //looping with integers (UNROLL 2)
  64.     {
  65.         high_resolution_clock::time_point t1 = high_resolution_clock::now();
  66.  
  67.         long long int sum = 0;
  68.         for (int i = 0; i<N; i+=2)
  69.             sum+=v[i]+v[i+1];
  70.  
  71.         high_resolution_clock::time_point t2 = high_resolution_clock::now();
  72.  
  73.         auto duration = std::chrono::duration_cast<std::chrono::microseconds>( t2 - t1 ).count();
  74.  
  75.         cout << duration << "microseconds  output = " << sum << " (integer index, UNROLL 2)\n";
  76.     }
  77.  
  78.     //looping with integers (UNROLL 4)
  79.     {
  80.         high_resolution_clock::time_point t1 = high_resolution_clock::now();
  81.  
  82.         long long int sum = 0;
  83.         for (int i = 0; i<N; i+=4)
  84.             sum+=v[i]+v[i+1]+v[i+2]+v[i+3];
  85.  
  86.         high_resolution_clock::time_point t2 = high_resolution_clock::now();
  87.  
  88.         auto duration = std::chrono::duration_cast<std::chrono::microseconds>( t2 - t1 ).count();
  89.  
  90.         cout << duration << "microseconds  output = " << sum << " (integer index, UNROLL 4)\n";
  91.     }
  92.  
  93.  
  94.     return 0;
  95. }
Success #stdin #stdout 0.13s 3140KB
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stdin
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Standard input is empty
stdout
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16532microseconds  output = 49999995000000 (Iterators)
16305microseconds  output = 49999995000000 (std::accumulate)
17227microseconds  output = 49999995000000 (integer index)
15919microseconds  output = 49999995000000 (integer index, UNROLL 2)
12807microseconds  output = 49999995000000 (integer index, UNROLL 4)
https://ideone.com/H7ekyv
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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