y.cc

#include <iostream>
#include <chrono>
#include <cstdlib>

int main() {
  const int N = 7*1024;

  int** m = new int*[N];
  int* n = new int[N*N];
  int* k = new int[N*N];

  for (int i = 0; i < N; i++) {
    m[i] = new int[N];
    for (int j = 0; j < N; j++) {
      const int r = arc4random();
      m[i][j] = r;
      n[i*N + j] = r;
      k[i*N + j] = r;
    }
  }

  using namespace std::chrono;
  time_point<system_clock> start, end;
  int elapsed;

  start = system_clock::now();
  for (int i = 0; i < N; i++) {
    for (int j = 0; j < N; j++) {
      m[i][j] += 42;
    }
  }
  end = system_clock::now();
  elapsed = duration_cast<milliseconds>(end - start).count();
  std::cout << elapsed << " ms\n";

  start = system_clock::now();
  for (int i = 0; i < N; i++) {
    for (int j = 0; j < N; j++) {
      n[j*N + i] += 42;
    }
  }
  end = system_clock::now();
  elapsed = duration_cast<milliseconds>(end - start).count();
  std::cout << elapsed << " ms\n";

  start = system_clock::now();
  for (int i = 0; i < N; i++) {
    for (int j = 0; j < N; j++) {
      k[i*N + j] += 42;
    }
  }
  end = system_clock::now();
  elapsed = duration_cast<milliseconds>(end - start).count();
  std::cout << elapsed << " ms\n";
}