fork(2) download
copy 
  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. struct timeit {
  5.     decltype(chrono::high_resolution_clock::now()) begin;
  6.     const string label;
  7.     timeit(string label = "???") : label(label) { begin = chrono::high_resolution_clock::now(); }
  8.     ~timeit() {
  9.         auto end = chrono::high_resolution_clock::now();
  10.         auto duration = chrono::duration_cast<chrono::milliseconds>(end - begin).count();
  11.         cerr << duration << "ms elapsed [" << label << "]" << endl;
  12.     }
  13. };
  14. const int MAXN = 1<<8;
  15. int i, j, a[MAXN][MAXN], rows[MAXN], cols[MAXN];
  16. const int NUMITERS = 10000;
  17. int main() {
  18.     for (int i=0; i<MAXN; i++) {
  19.         rows[i] = i;
  20.         cols[i] = i;
  21.     }
  22.     {
  23.         timeit timer("blocked");
  24.         int n = MAXN;
  25.         int B = 8;
  26.         for (int t = 0; t < NUMITERS; t++) {
  27.             for (int i = 0; i < n; i += B) {
  28.                 for (int j = 0; j < n; j += B) {
  29.                     for (int x = i; x < i + B; x++) {
  30.                         for (int y = j; y < j + B; y++) {
  31.                             a[x][y] = rows[x] * cols[y];
  32.                         }
  33.                     }
  34.                 }
  35.             }
  36.         }
  37.         cout<<a[20][20]<<endl;
  38.     }
  39.     {
  40.         timeit x("normal");
  41.         int n = MAXN;
  42.         for (int t = 0; t < NUMITERS; t++) {
  43.             for (i = 0; i < MAXN; i++) {
  44.                 for (j = 0; j < MAXN; j++) {
  45.                     a[i][j] = rows[i]*cols[j];
  46.                 }
  47.             }
  48.         }
  49.         cout<<a[20][20]<<endl;
  50.     }
  51. }
  52.  
Success #stdin #stdout #stderr 0.99s 4384KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
400
400
stderr
copy 
600ms elapsed [blocked]
386ms elapsed [normal]
https://ideone.com/4HRl3F
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!