1 use super::map::MIN_LEN;
2 use super::node::{marker, ForceResult::*, Handle, LeftOrRight::*, NodeRef};
4 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::KV> {
5 /// Removes a key-value pair from the tree, and returns that pair, as well as
6 /// the leaf edge corresponding to that former pair. It's possible this empties
7 /// a root node that is internal, which the caller should pop from the map
8 /// holding the tree. The caller should also decrement the map's length.
9 pub fn remove_kv_tracking<F: FnOnce()>(
11 handle_emptied_internal_root: F,
12 ) -> ((K, V), Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>) {
14 Leaf(node) => node.remove_leaf_kv(handle_emptied_internal_root),
15 Internal(node) => node.remove_internal_kv(handle_emptied_internal_root),
20 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
21 fn remove_leaf_kv<F: FnOnce()>(
23 handle_emptied_internal_root: F,
24 ) -> ((K, V), Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>) {
25 let (old_kv, mut pos) = self.remove();
26 let len = pos.reborrow().into_node().len();
29 // We have to temporarily forget the child type, because there is no
30 // distinct node type for the immediate parents of a leaf.
31 let new_pos = match pos.into_node().forget_type().choose_parent_kv() {
32 Ok(Left(left_parent_kv)) => {
33 debug_assert!(left_parent_kv.right_child_len() == MIN_LEN - 1);
34 if left_parent_kv.can_merge() {
35 left_parent_kv.merge_tracking_child_edge(Right(idx))
37 debug_assert!(left_parent_kv.left_child_len() > MIN_LEN);
38 left_parent_kv.steal_left(idx)
41 Ok(Right(right_parent_kv)) => {
42 debug_assert!(right_parent_kv.left_child_len() == MIN_LEN - 1);
43 if right_parent_kv.can_merge() {
44 right_parent_kv.merge_tracking_child_edge(Left(idx))
46 debug_assert!(right_parent_kv.right_child_len() > MIN_LEN);
47 right_parent_kv.steal_right(idx)
50 Err(pos) => unsafe { Handle::new_edge(pos, idx) },
52 // SAFETY: `new_pos` is the leaf we started from or a sibling.
53 pos = unsafe { new_pos.cast_to_leaf_unchecked() };
55 // Only if we merged, the parent (if any) has shrunk, but skipping
56 // the following step otherwise does not pay off in benchmarks.
58 // SAFETY: We won't destroy or rearrange the leaf where `pos` is at
59 // by handling its parent recursively; at worst we will destroy or
60 // rearrange the parent through the grandparent, thus change the
61 // link to the parent inside the leaf.
62 if let Ok(parent) = unsafe { pos.reborrow_mut() }.into_node().ascend() {
63 parent.into_node().handle_shrunk_node_recursively(handle_emptied_internal_root);
70 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> {
71 fn remove_internal_kv<F: FnOnce()>(
73 handle_emptied_internal_root: F,
74 ) -> ((K, V), Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>) {
75 // Remove an adjacent KV from its leaf and then put it back in place of
76 // the element we were asked to remove. Prefer the left adjacent KV,
77 // for the reasons listed in `choose_parent_kv`.
78 let left_leaf_kv = self.left_edge().descend().last_leaf_edge().left_kv();
79 let left_leaf_kv = unsafe { left_leaf_kv.ok().unwrap_unchecked() };
80 let (left_kv, left_hole) = left_leaf_kv.remove_leaf_kv(handle_emptied_internal_root);
82 // The internal node may have been stolen from or merged. Go back right
83 // to find where the original KV ended up.
84 let mut internal = unsafe { left_hole.next_kv().ok().unwrap_unchecked() };
85 let old_kv = internal.replace_kv(left_kv.0, left_kv.1);
86 let pos = internal.next_leaf_edge();
91 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
92 /// Stocks up a possibly underfull internal node and its ancestors,
93 /// until it reaches an ancestor that has elements to spare or is the root.
94 fn handle_shrunk_node_recursively<F: FnOnce()>(mut self, handle_emptied_internal_root: F) {
96 self = match self.len() {
98 // An empty node must be the root, because length is only
99 // reduced by one, and non-root underfull nodes are stocked up,
100 // so non-root nodes never have fewer than MIN_LEN - 1 elements.
101 debug_assert!(self.ascend().is_err());
102 handle_emptied_internal_root();
106 if let Some(parent) = self.handle_underfull_node_locally() {
117 /// Stocks up an underfull internal node, possibly at the cost of shrinking
118 /// its parent instead, which is then returned.
119 fn handle_underfull_node_locally(
121 ) -> Option<NodeRef<marker::Mut<'a>, K, V, marker::Internal>> {
122 match self.forget_type().choose_parent_kv() {
123 Ok(Left(mut left_parent_kv)) => {
124 debug_assert_eq!(left_parent_kv.right_child_len(), MIN_LEN - 1);
125 if left_parent_kv.can_merge() {
126 let parent = left_parent_kv.merge_tracking_parent();
129 debug_assert!(left_parent_kv.left_child_len() > MIN_LEN);
130 left_parent_kv.bulk_steal_left(1);
134 Ok(Right(mut right_parent_kv)) => {
135 debug_assert_eq!(right_parent_kv.left_child_len(), MIN_LEN - 1);
136 if right_parent_kv.can_merge() {
137 let parent = right_parent_kv.merge_tracking_parent();
140 debug_assert!(right_parent_kv.right_child_len() > MIN_LEN);
141 right_parent_kv.bulk_steal_right(1);