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  1. #include <chrono>
  2. #include <iostream>
  3. #include <random>
  4. #include <algorithm>
  5. #include <iterator>
  6. #include <functional>
  7.  
  8. using namespace std;
  9.  
  10. int main()
  11. {
  12.     //Generate a vector of random integers from 1 to 100
  13.     random_device rnd_device;
  14.     mt19937 rnd_engine(rnd_device());
  15.     uniform_int_distribution<int> rnd_dist(1, 100);
  16.     auto gen = std::bind(rnd_dist, rnd_engine);
  17.     vector<int> rand_vec(5000);
  18.     generate(begin(rand_vec), end(rand_vec), gen);
  19.     volatile int nLow, nMid, nHigh;
  20.  
  21.     //Count the number of values in each of three different ranges
  22.     //Run the test a few times
  23.     for (int n = 0; n != 10; ++n) {
  24. {
  25.           //Sort the conditional statements in order of likelyhood
  26.           nLow = nMid = nHigh = 0;
  27.           auto start = chrono::high_resolution_clock::now();
  28.           for (int& i : rand_vec) {
  29.               if (i >= 20 && i < 95) ++nMid;  //Most likely branch
  30.               else if (i < 20) ++nLow;
  31.               else if (i >= 95) ++nHigh;      //Least likely branch
  32.           }
  33.           auto end = chrono::high_resolution_clock::now();
  34.           cout << "Sorted:\t\t\t" << chrono::duration_cast<chrono::nanoseconds>(end-start).count() << "ns" << endl;
  35.         }
  36.  
  37.         //Run the test again, but now sort the conditional statements in reverse-order of likelyhood
  38.         {
  39.           nLow = nMid = nHigh = 0;
  40.           auto start = chrono::high_resolution_clock::now();
  41.           for (int& i : rand_vec) {
  42.               if (i >= 95) ++nHigh;               //Least likely branch
  43.               else if (i < 20) ++nLow;
  44.               else if (i >= 20 && i < 95) ++nMid; //Most likely branch
  45.           }
  46.           auto end = chrono::high_resolution_clock::now();
  47.           cout << "Reverse-sorted: \t" << chrono::duration_cast<chrono::nanoseconds>(end-start).count() << "ns" << endl;
  48.         }
  49.  
  50.  
  51.         cout << endl;
  52.     }
  53. }
Success #stdin #stdout 0s 15240KB
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stdin
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Standard input is empty
stdout
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Sorted:			15839ns
Reverse-sorted: 	14896ns

Sorted:			15049ns
Reverse-sorted: 	14245ns

Sorted:			13613ns
Reverse-sorted: 	13869ns

Sorted:			12819ns
Reverse-sorted: 	13196ns

Sorted:			12137ns
Reverse-sorted: 	12499ns

Sorted:			11439ns
Reverse-sorted: 	12255ns

Sorted:			11401ns
Reverse-sorted: 	12738ns

Sorted:			10848ns
Reverse-sorted: 	12667ns

Sorted:			10663ns
Reverse-sorted: 	12363ns

Sorted:			10403ns
Reverse-sorted: 	12083ns
https://ideone.com/qA7qLE
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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