Method swap

src/include/cpp-btree/btree.h:1689–1732

template <typename P>
void btree_node<P>::swap(btree_node *x, allocator_type *alloc) {
  using std::swap;
  assert(leaf() == x->leaf());

  // Determine which is the smaller/larger node.
  btree_node *smaller = this, *larger = x;
  if (smaller->count() > larger->count()) {
    swap(smaller, larger);
  }

  // Swap the values.
  std::swap_ranges(smaller->slot(0), smaller->slot(smaller->count()),
                   larger->slot(0));

  // Move values that can't be swapped.
  const size_type to_move = larger->count() - smaller->count();
  larger->uninitialized_move_n(to_move, smaller->count(), smaller->count(),
                               smaller, alloc);
  larger->value_destroy_n(smaller->count(), to_move, alloc);

  if (!leaf()) {
    // Swap the child pointers.
    auto* smaller_begin = &smaller->mutable_child(0);
    auto* larger_begin = &larger->mutable_child(0);
    auto count = smaller->count() + 1;
    std::swap_ranges(smaller_begin,
                     smaller_begin + count,
                     larger_begin);
    // Update swapped children's parent pointers.
    int i = 0;
    for (; i <= smaller->count(); ++i) {
      smaller->child(i)->set_parent(smaller);
      larger->child(i)->set_parent(larger);
    }
    // Move the child pointers that couldn't be swapped.
    for (; i <= larger->count(); ++i) {
      smaller->init_child(i, larger->child(i));
      larger->clear_child(i);
    }
  }

  // Swap the counts.
  swap(mutable_count(), x->mutable_count());
}

////
// btree_iterator methods