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  1. #include <iostream>
  2. #include <algorithm>
  3. #include <ctime>
  4.  
  5.  
  6. using namespace std;
  7.  
  8. class mytimer
  9. {
  10.  public:
  11.   mytimer() { _start_time = clock(); }
  12.   void   restart() { _start_time = clock(); }
  13.   clock_t elapsed() const
  14.   { return  clock() - _start_time; }
  15.  
  16.  private:
  17.   clock_t  _start_time;
  18. }; // timer
  19.  
  20. int main()
  21. {
  22.     const int num_samples = 1000;
  23.     float* samples = new float[num_samples];
  24.     mytimer timer;
  25.     for (int x = 0 ; x != 100000 ; x++) {
  26.     for (int i = 0; i < num_samples; i++) {
  27.         samples[i] = 1.f;
  28.     }
  29.     }
  30.     double result = timer.elapsed();
  31.     std::cout << "rewrite of " << (num_samples*sizeof(float)/(1024*1024)) << " Mb takes " << result << std::endl;
  32.  
  33.     timer.restart();
  34.     float sum;
  35.     for (int x = 0 ; x != 100000 ; x++) {
  36.     	sum=0;
  37.     for (int i = 0; i < num_samples; i++) {
  38.         sum += samples[i];
  39.     }
  40.     }
  41.     result = timer.elapsed();
  42.     std::cout << "naive:\t\t" << result << ", sum = " << sum << std::endl;
  43.  
  44.     timer.restart();
  45.     float* end = samples + num_samples;
  46.     for (int x = 0 ; x != 100000 ; x++) {
  47.     sum = 0;
  48.     for(float* i = samples; i < end; i++) {
  49.         sum += *i;
  50.     }
  51.     }
  52.     result = timer.elapsed();
  53.     std::cout << "pointers:\t" << result << ", sum = " << sum << std::endl;
  54.  
  55.     timer.restart();
  56.     sum = 0;
  57.     for (int x = 0 ; x != 100000 ; x++) {
  58.  
  59.     sum = std::accumulate(samples, end, 0.0F);
  60.     }
  61.     result = timer.elapsed();
  62.     std::cout << "algorithm:\t" << result << ", sum = " << sum << std::endl;
  63.  
  64. }
  65.  
Success #stdin #stdout 0.63s 3472KB
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stdin
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Standard input is empty
stdout
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rewrite of 0 Mb takes 90000
naive:		180000, sum = 1000
pointers:	180000, sum = 1000
algorithm:	180000, sum = 1000
https://ideone.com/XXtnyR
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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