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BTreeMap: gather and decompose reusable tree fixing functions
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,171 @@ | ||
| use super::map::MIN_LEN; | ||
| use super::node::{marker, ForceResult::*, Handle, LeftOrRight::*, NodeRef, Root}; | ||
|
|
||
| impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> { | ||
| /// Stocks up a possibly underfull node by merging with or stealing from a | ||
| /// sibling. If succesful but at the cost of shrinking the parent node, | ||
| /// returns that shrunk parent node. Returns an `Err` if the node is | ||
| /// an empty root. | ||
| fn fix_node_through_parent( | ||
| self, | ||
| ) -> Result<Option<NodeRef<marker::Mut<'a>, K, V, marker::Internal>>, Self> { | ||
| let len = self.len(); | ||
| if len >= MIN_LEN { | ||
| Ok(None) | ||
| } else { | ||
| match self.choose_parent_kv() { | ||
| Ok(Left(mut left_parent_kv)) => { | ||
| if left_parent_kv.can_merge() { | ||
| let parent = left_parent_kv.merge_tracking_parent(); | ||
| Ok(Some(parent)) | ||
| } else { | ||
| left_parent_kv.bulk_steal_left(MIN_LEN - len); | ||
| Ok(None) | ||
| } | ||
| } | ||
| Ok(Right(mut right_parent_kv)) => { | ||
| if right_parent_kv.can_merge() { | ||
| let parent = right_parent_kv.merge_tracking_parent(); | ||
| Ok(Some(parent)) | ||
| } else { | ||
| right_parent_kv.bulk_steal_right(MIN_LEN - len); | ||
| Ok(None) | ||
| } | ||
| } | ||
| Err(root) => { | ||
| if len > 0 { | ||
| Ok(None) | ||
| } else { | ||
| Err(root) | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> { | ||
| /// Stocks up a possibly underfull node, and if that causes its parent node | ||
| /// to shrink, stocks up the parent, recursively. | ||
| /// Returns `true` if it fixed the tree, `false` if it couldn't because the | ||
| /// root node became empty. | ||
| /// | ||
| /// This method does not expect ancestors to already be underfull upon entry | ||
| /// and panics if it encounters an empty ancestor. | ||
| pub fn fix_node_and_affected_ancestors(mut self) -> bool { | ||
| loop { | ||
| match self.fix_node_through_parent() { | ||
| Ok(Some(parent)) => self = parent.forget_type(), | ||
| Ok(None) => return true, | ||
| Err(_) => return false, | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl<K, V> Root<K, V> { | ||
| /// Removes empty levels on the top, but keeps an empty leaf if the entire tree is empty. | ||
| pub fn fix_top(&mut self) { | ||
| while self.height() > 0 && self.len() == 0 { | ||
| self.pop_internal_level(); | ||
| } | ||
| } | ||
|
|
||
| /// Stocks up or merge away any underfull nodes on the right border of the | ||
| /// tree. The other nodes, those that are not the root nor a rightmost edge, | ||
| /// must already have at least MIN_LEN elements. | ||
| pub fn fix_right_border(&mut self) { | ||
| self.fix_top(); | ||
| if self.len() > 0 { | ||
| self.borrow_mut().last_kv().fix_right_border_of_right_edge(); | ||
| self.fix_top(); | ||
| } | ||
| } | ||
|
|
||
| /// The symmetric clone of `fix_right_border`. | ||
| pub fn fix_left_border(&mut self) { | ||
| self.fix_top(); | ||
| if self.len() > 0 { | ||
| self.borrow_mut().first_kv().fix_left_border_of_left_edge(); | ||
| self.fix_top(); | ||
| } | ||
| } | ||
|
|
||
| /// Stock up any underfull nodes on the right border of the tree. | ||
| /// The other nodes, those that are not the root nor a rightmost edge, | ||
| /// must be prepared to have up to MIN_LEN elements stolen. | ||
| pub fn fix_right_border_of_plentiful(&mut self) { | ||
| let mut cur_node = self.borrow_mut(); | ||
| while let Internal(internal) = cur_node.force() { | ||
| // Check if right-most child is underfull. | ||
| let mut last_kv = internal.last_kv().consider_for_balancing(); | ||
| debug_assert!(last_kv.left_child_len() >= MIN_LEN * 2); | ||
| let right_child_len = last_kv.right_child_len(); | ||
| if right_child_len < MIN_LEN { | ||
| // We need to steal. | ||
| last_kv.bulk_steal_left(MIN_LEN - right_child_len); | ||
| } | ||
|
|
||
| // Go further down. | ||
| cur_node = last_kv.into_right_child(); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::KV> { | ||
| fn fix_left_border_of_left_edge(mut self) { | ||
| while let Internal(internal_kv) = self.force() { | ||
| self = internal_kv.fix_left_child().first_kv(); | ||
| debug_assert!(self.reborrow().into_node().len() > MIN_LEN); | ||
| } | ||
| } | ||
|
|
||
| fn fix_right_border_of_right_edge(mut self) { | ||
| while let Internal(internal_kv) = self.force() { | ||
| self = internal_kv.fix_right_child().last_kv(); | ||
| debug_assert!(self.reborrow().into_node().len() > MIN_LEN); | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> { | ||
| /// Stocks up the left child, assuming the right child isn't underfull, and | ||
| /// provisions an extra element to allow merging its children in turn | ||
| /// without becoming underfull. | ||
| /// Returns the left child. | ||
| fn fix_left_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> { | ||
| let mut internal_kv = self.consider_for_balancing(); | ||
| let left_len = internal_kv.left_child_len(); | ||
| debug_assert!(internal_kv.right_child_len() >= MIN_LEN); | ||
| if internal_kv.can_merge() { | ||
| internal_kv.merge_tracking_child() | ||
| } else { | ||
| // `MIN_LEN + 1` to avoid readjust if merge happens on the next level. | ||
| let count = (MIN_LEN + 1).saturating_sub(left_len); | ||
| if count > 0 { | ||
| internal_kv.bulk_steal_right(count); | ||
| } | ||
| internal_kv.into_left_child() | ||
| } | ||
| } | ||
|
|
||
| /// Stocks up the right child, assuming the left child isn't underfull, and | ||
| /// provisions an extra element to allow merging its children in turn | ||
| /// without becoming underfull. | ||
| /// Returns wherever the right child ended up. | ||
| fn fix_right_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> { | ||
| let mut internal_kv = self.consider_for_balancing(); | ||
| let right_len = internal_kv.right_child_len(); | ||
| debug_assert!(internal_kv.left_child_len() >= MIN_LEN); | ||
| if internal_kv.can_merge() { | ||
| internal_kv.merge_tracking_child() | ||
| } else { | ||
| // `MIN_LEN + 1` to avoid readjust if merge happens on the next level. | ||
| let count = (MIN_LEN + 1).saturating_sub(right_len); | ||
| if count > 0 { | ||
| internal_kv.bulk_steal_left(count); | ||
| } | ||
| internal_kv.into_right_child() | ||
| } | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,5 +1,6 @@ | ||
| mod append; | ||
| mod borrow; | ||
| mod fix; | ||
| pub mod map; | ||
| mod mem; | ||
| mod merge_iter; | ||
|
|
||
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