From 698f8c2f01ea549d77d7dc3338a12e04c11057b9 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Wed, 17 Apr 2024 14:02:58 +0200 Subject: Adding upstream version 1.64.0+dfsg1. Signed-off-by: Daniel Baumann --- library/alloc/src/collections/btree/fix.rs | 179 +++++++++++++++++++++++++++++ 1 file changed, 179 insertions(+) create mode 100644 library/alloc/src/collections/btree/fix.rs (limited to 'library/alloc/src/collections/btree/fix.rs') diff --git a/library/alloc/src/collections/btree/fix.rs b/library/alloc/src/collections/btree/fix.rs new file mode 100644 index 000000000..91b612180 --- /dev/null +++ b/library/alloc/src/collections/btree/fix.rs @@ -0,0 +1,179 @@ +use super::map::MIN_LEN; +use super::node::{marker, ForceResult::*, Handle, LeftOrRight::*, NodeRef, Root}; +use core::alloc::Allocator; + +impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::LeafOrInternal> { + /// Stocks up a possibly underfull node by merging with or stealing from a + /// sibling. If successful 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, + alloc: A, + ) -> Result, 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(alloc); + 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(alloc); + 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, 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, alloc: A) -> bool { + loop { + match self.fix_node_through_parent(alloc.clone()) { + Ok(Some(parent)) => self = parent.forget_type(), + Ok(None) => return true, + Err(_) => return false, + } + } + } +} + +impl Root { + /// Removes empty levels on the top, but keeps an empty leaf if the entire tree is empty. + pub fn fix_top(&mut self, alloc: A) { + while self.height() > 0 && self.len() == 0 { + self.pop_internal_level(alloc.clone()); + } + } + + /// 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, alloc: A) { + self.fix_top(alloc.clone()); + if self.len() > 0 { + self.borrow_mut().last_kv().fix_right_border_of_right_edge(alloc.clone()); + self.fix_top(alloc); + } + } + + /// The symmetric clone of `fix_right_border`. + pub fn fix_left_border(&mut self, alloc: A) { + self.fix_top(alloc.clone()); + if self.len() > 0 { + self.borrow_mut().first_kv().fix_left_border_of_left_edge(alloc.clone()); + self.fix_top(alloc); + } + } + + /// Stocks up any underfull nodes on the right border of the tree. + /// The other nodes, those that are neither 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, K, V, marker::LeafOrInternal>, marker::KV> { + fn fix_left_border_of_left_edge(mut self, alloc: A) { + while let Internal(internal_kv) = self.force() { + self = internal_kv.fix_left_child(alloc.clone()).first_kv(); + debug_assert!(self.reborrow().into_node().len() > MIN_LEN); + } + } + + fn fix_right_border_of_right_edge(mut self, alloc: A) { + while let Internal(internal_kv) = self.force() { + self = internal_kv.fix_right_child(alloc.clone()).last_kv(); + debug_assert!(self.reborrow().into_node().len() > MIN_LEN); + } + } +} + +impl<'a, K: 'a, V: 'a> Handle, 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, + alloc: A, + ) -> NodeRef, 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(alloc) + } 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, + alloc: A, + ) -> NodeRef, 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(alloc) + } 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() + } + } +} -- cgit v1.2.3