#include <time.h>
#include <stdio.h>
#include <stdint.h>

#define SIZE (1<<13)
int box[SIZE][SIZE]; // A big 2D array

// A high-resolution timer counting in microseconds
uint64_t microseconds() { 
  #pragma inline
  struct timespec ts;
  clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts);
  uint64_t ans = ts.tv_sec * 1000000;
  ans += ts.tv_nsec / 1000;
  return ans;
}

// Run two loops, getting the time before and after each
int main(int argc, char *argv[]) {
  uint64_t t0 = microseconds();
  
  for(int i=0; i<SIZE; i+=1)
    for(int j=0; j<SIZE; j+=1)
      box[i][j] = i*2+i;
  
  uint64_t t1 = microseconds();
  
  for(int j=0; j<SIZE; j+=1)
    for(int i=0; i<SIZE; i+=1)
      box[i][j] = i*2+j;
  
  uint64_t t2 = microseconds();
  printf("Time used in first loop:  %8lu µs\n", t1-t0);
  printf("Time used in second loop: %8lu µs\n", t2-t1);
}