void quicksort (quickarg qa) {
  pthread_t thread1, thread2;
  int pivot  = qa.premier;
  int dernier = qa.dernier;
  int ret;

  if (qa.premier < qa.dernier) {
    pivot = quicksort_partitionner(qa.tab, qa.premier, qa.dernier, pivot);

    qa.dernier = pivot - 1;
    pthread_create (&thread1, NULL, (void *) &quicksort, (void *) &qa);
    qa.premier = pivot + 1;
    qa.dernier = dernier;
    pthread_create (&thread2, NULL, (void *) &quicksort, (void *) &qa);

    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);
  }
}