From d1a2c0f99c079479009b879fd904859438b72f1e Mon Sep 17 00:00:00 2001 From: Stein Somers Date: Thu, 5 Nov 2020 13:23:11 +0100 Subject: [PATCH] BTreeMap: try to enhance various comments & local identifiers --- .../alloc/src/collections/btree/map/entry.rs | 2 +- .../alloc/src/collections/btree/navigate.rs | 9 + library/alloc/src/collections/btree/node.rs | 168 ++++++++++-------- library/alloc/src/collections/btree/remove.rs | 2 +- library/alloc/src/collections/btree/search.rs | 20 ++- library/alloc/src/collections/btree/set.rs | 2 +- library/alloc/src/collections/btree/split.rs | 4 +- 7 files changed, 118 insertions(+), 89 deletions(-) diff --git a/library/alloc/src/collections/btree/map/entry.rs b/library/alloc/src/collections/btree/map/entry.rs index 69926ac2aff6d..c92888cb8973c 100644 --- a/library/alloc/src/collections/btree/map/entry.rs +++ b/library/alloc/src/collections/btree/map/entry.rs @@ -459,7 +459,7 @@ impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> { self.remove_kv().1 } - // Body of `remove_entry`, separate to keep the above implementations short. + // Body of `remove_entry`, probably separate because the name reflects the returned pair. pub(super) fn remove_kv(self) -> (K, V) { let mut emptied_internal_root = false; let (old_kv, _) = self.handle.remove_kv_tracking(|| emptied_internal_root = true); diff --git a/library/alloc/src/collections/btree/navigate.rs b/library/alloc/src/collections/btree/navigate.rs index ef6f888693fc8..cce8b21a2bc41 100644 --- a/library/alloc/src/collections/btree/navigate.rs +++ b/library/alloc/src/collections/btree/navigate.rs @@ -9,6 +9,9 @@ use super::search::{self, SearchResult}; use super::unwrap_unchecked; /// Finds the leaf edges delimiting a specified range in or underneath a node. +/// +/// The result is meaningful only if the tree is ordered by key, like the tree +/// in a `BTreeMap` is. fn range_search( root1: NodeRef, root2: NodeRef, @@ -122,6 +125,9 @@ fn full_range( impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::LeafOrInternal> { /// Creates a pair of leaf edges delimiting a specified range in or underneath a node. + /// + /// The result is meaningful only if the tree is ordered by key, like the tree + /// in a `BTreeMap` is. pub fn range_search( self, range: R, @@ -152,6 +158,9 @@ impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::LeafOrInternal> /// Splits a unique reference into a pair of leaf edges delimiting a specified range. /// The result are non-unique references allowing (some) mutation, which must be used /// carefully. + /// + /// The result is meaningful only if the tree is ordered by key, like the tree + /// in a `BTreeMap` is. pub fn range_search( self, range: R, diff --git a/library/alloc/src/collections/btree/node.rs b/library/alloc/src/collections/btree/node.rs index 6a8be441513a0..78be070a98382 100644 --- a/library/alloc/src/collections/btree/node.rs +++ b/library/alloc/src/collections/btree/node.rs @@ -27,6 +27,9 @@ // given node has exactly the same length. // - A node of length `n` has `n` keys, `n` values, and `n + 1` edges. // This implies that even an empty node has at least one edge. +// For a leaf node, "having an edge" only means we can identify a position in the node, +// since leaf edges are empty and need no data representation. In an internal node, +// an edge both identifies a position and contains a pointer to a child node. use core::cmp::Ordering; use core::marker::PhantomData; @@ -215,6 +218,8 @@ impl NodeRef { /// although insert methods allow a mutable pointer to a value to coexist. /// - When this is `Owned`, the `NodeRef` acts roughly like `Box`, /// but does not have a destructor, and must be cleaned up manually. +/// Since any `NodeRef` allows navigating through the tree, `BorrowType` +/// effectively applies to the entire tree, not just the node itself. /// - `K` and `V`: These are the types of keys and values stored in the nodes. /// - `Type`: This can be `Leaf`, `Internal`, or `LeafOrInternal`. When this is /// `Leaf`, the `NodeRef` points to a leaf node, when this is `Internal` the @@ -227,9 +232,9 @@ impl NodeRef { /// such restrictions: /// - For each type parameter, we can only define a method either generically /// or for one particular type. For example, we cannot define a method like -/// `key_at` generically for all `BorrowType`, because we want to return +/// `key_at` generically for all `BorrowType`, because we want it to return /// `&'a K` for most choices of `BorrowType`, but plain `K` for `Owned`. -/// We cannot define `key_at` once for all types that have a lifetime. +/// We cannot define `key_at` once for all types that carry a lifetime. /// Therefore, we define it only for the least powerful type `Immut<'a>`. /// - We cannot get implicit coercion from say `Mut<'a>` to `Immut<'a>`. /// Therefore, we have to explicitly call `reborrow` on a more powerfull @@ -240,16 +245,17 @@ impl NodeRef { /// That is irrelevant when `BorrowType` is `Immut<'a>`, but the rule does /// no harm because we make those `NodeRef` implicitly `Copy`. /// The rule also avoids implicitly returning the lifetime of `&self`, -/// instead of the lifetime contained in `BorrowType`. +/// instead of the lifetime carried by `BorrowType`. /// An exception to this rule are the insert functions. /// - Given the above, we need a `reborrow_mut` to explicitly copy a `Mut<'a>` /// `NodeRef` whenever we want to invoke a method returning an extra reference /// somewhere in the tree. pub struct NodeRef { - /// The number of levels below the node, a property of the node that cannot be - /// entirely described by `Type` and that the node does not store itself either. - /// Unconstrained if `Type` is `LeafOrInternal`, must be zero if `Type` is `Leaf`, - /// and must be non-zero if `Type` is `Internal`. + /// The number of levels that the node and the level of leaves are apart, a + /// constant of the node that cannot be entirely described by `Type`, and that + /// the node itself does not store. We only need to store the height of the root + /// node, and derive every other node's height from it. + /// Must be zero if `Type` is `Leaf` and non-zero if `Type` is `Internal`. height: usize, /// The pointer to the leaf or internal node. The definition of `InternalNode` /// ensures that the pointer is valid either way. @@ -317,8 +323,11 @@ impl NodeRef { unsafe { usize::from((*Self::as_leaf_ptr(self)).len) } } - /// Returns the height of this node with respect to the leaf level. Zero height means the - /// node is a leaf itself. + /// Returns the number of levels that the node and leaves are apart. Zero + /// height means the node is a leaf itself. If you picture trees with the + /// root on top, the number says at which elevation the node appears. + /// If you picture trees with leaves on top, the number says how high + /// the tree extends above the node. pub fn height(&self) -> usize { self.height } @@ -376,6 +385,8 @@ impl NodeRef { /// that points to the current node. Returns `Err(self)` if the current node has /// no parent, giving back the original `NodeRef`. /// + /// The method name assumes you picture trees with the root node on top. + /// /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should /// both, upon success, do nothing. pub fn ascend( @@ -576,7 +587,6 @@ impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::Internal> { impl<'a, K, V, Type> NodeRef, K, V, Type> { /// # Safety /// - The node has more than `idx` initialized elements. - /// - The keys and values of the node must be initialized up to its current length. unsafe fn into_key_val_mut_at(mut self, idx: usize) -> (&'a K, &'a mut V) { // We only create a reference to the one element we are interested in, // to avoid aliasing with outstanding references to other elements, @@ -609,7 +619,7 @@ impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::LeafOrInternal> { unsafe { (*leaf).parent_idx.write(parent_idx as u16) }; } - /// Clear the node's link to its parent edge, freeing it from its tree. + /// Clear the node's link to its parent edge. /// This only makes sense when there are no other references to the node. fn clear_parent_link(&mut self) { let leaf = Self::as_leaf_mut(self); @@ -618,7 +628,7 @@ impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::LeafOrInternal> { } impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::Leaf> { - /// Adds a key/value pair to the end of the node. + /// Adds a key-value pair to the end of the node. pub fn push(&mut self, key: K, val: V) { let len = unsafe { self.reborrow_mut().into_len_mut() }; let idx = usize::from(*len); @@ -630,7 +640,7 @@ impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::Leaf> { } } - /// Adds a key/value pair to the beginning of the node. + /// Adds a key-value pair to the beginning of the node. fn push_front(&mut self, key: K, val: V) { assert!(self.len() < CAPACITY); @@ -659,7 +669,7 @@ impl<'a, K, V> NodeRef, K, V, marker::Internal> { } impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::Internal> { - /// Adds a key/value pair, and an edge to go to the right of that pair, + /// Adds a key-value pair, and an edge to go to the right of that pair, /// to the end of the node. pub fn push(&mut self, key: K, val: V, edge: Root) { assert!(edge.height == self.height - 1); @@ -676,7 +686,7 @@ impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::Internal> { } } - /// Adds a key/value pair, and an edge to go to the left of that pair, + /// Adds a key-value pair, and an edge to go to the left of that pair, /// to the beginning of the node. fn push_front(&mut self, key: K, val: V, edge: Root) { assert!(edge.height == self.height - 1); @@ -694,7 +704,7 @@ impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::Internal> { } impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::LeafOrInternal> { - /// Removes a key/value pair from the end of the node and returns the pair. + /// Removes a key-value pair from the end of the node and returns the pair. /// Also removes the edge that was to the right of that pair and, if the node /// is internal, returns the orphaned subtree that this edge owned. fn pop(&mut self) -> (K, V, Option>) { @@ -722,7 +732,7 @@ impl<'a, K: 'a, V: 'a> NodeRef, K, V, marker::LeafOrInternal> { } } - /// Removes a key/value pair from the beginning of the node and returns the pair. + /// Removes a key-value pair from the beginning of the node and returns the pair. /// Also removes the edge that was to the left of that pair and, if the node is /// internal, returns the orphaned subtree that this edge owned. fn pop_front(&mut self) -> (K, V, Option>) { @@ -786,12 +796,12 @@ impl NodeRef { } } -/// A reference to a specific key/value pair or edge within a node. The `Node` parameter -/// must be a `NodeRef`, while the `Type` can either be `KV` (signifying a handle on a key/value +/// A reference to a specific key-value pair or edge within a node. The `Node` parameter +/// must be a `NodeRef`, while the `Type` can either be `KV` (signifying a handle on a key-value /// pair) or `Edge` (signifying a handle on an edge). /// /// Note that even `Leaf` nodes can have `Edge` handles. Instead of representing a pointer to -/// a child node, these represent the spaces where child pointers would go between the key/value +/// a child node, these represent the spaces where child pointers would go between the key-value /// pairs. For example, in a node with length 2, there would be 3 possible edge locations - one /// to the left of the node, one between the two pairs, and one at the right of the node. pub struct Handle { @@ -810,7 +820,7 @@ impl Clone for Handle { } impl Handle { - /// Retrieves the node that contains the edge or key/value pair this handle points to. + /// Retrieves the node that contains the edge or key-value pair this handle points to. pub fn into_node(self) -> Node { self.node } @@ -822,7 +832,7 @@ impl Handle { } impl Handle, marker::KV> { - /// Creates a new handle to a key/value pair in `node`. + /// Creates a new handle to a key-value pair in `node`. /// Unsafe because the caller must ensure that `idx < node.len()`. pub unsafe fn new_kv(node: NodeRef, idx: usize) -> Self { debug_assert!(idx < node.len()); @@ -842,7 +852,7 @@ impl Handle, mar impl NodeRef { /// Could be a public implementation of PartialEq, but only used in this module. fn eq(&self, other: &Self) -> bool { - let Self { node, height, _marker: _ } = self; + let Self { node, height, _marker } = self; if node.eq(&other.node) { debug_assert_eq!(*height, other.height); true @@ -856,7 +866,7 @@ impl PartialEq for Handle, HandleType> { fn eq(&self, other: &Self) -> bool { - let Self { node, idx, _marker: _ } = self; + let Self { node, idx, _marker } = self; node.eq(&other.node) && *idx == other.idx } } @@ -865,7 +875,7 @@ impl PartialOrd for Handle, HandleType> { fn partial_cmp(&self, other: &Self) -> Option { - let Self { node, idx, _marker: _ } = self; + let Self { node, idx, _marker } = self; if node.eq(&other.node) { Some(idx.cmp(&other.idx)) } else { None } } } @@ -950,7 +960,7 @@ fn splitpoint(edge_idx: usize) -> (usize, LeftOrRight) { } impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Leaf>, marker::Edge> { - /// Inserts a new key/value pair between the key/value pairs to the right and left of + /// Inserts a new key-value pair between the key-value pairs to the right and left of /// this edge. This method assumes that there is enough space in the node for the new /// pair to fit. /// @@ -969,7 +979,7 @@ impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Leaf>, mark } impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Leaf>, marker::Edge> { - /// Inserts a new key/value pair between the key/value pairs to the right and left of + /// Inserts a new key-value pair between the key-value pairs to the right and left of /// this edge. This method splits the node if there isn't enough room. /// /// The returned pointer points to the inserted value. @@ -997,8 +1007,8 @@ impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Leaf>, mark } impl<'a, K, V> Handle, K, V, marker::Internal>, marker::Edge> { - /// Fixes the parent pointer and index in the child node below this edge. This is useful - /// when the ordering of edges has been changed, such as in the various `insert` methods. + /// Fixes the parent pointer and index in the child node that this edge + /// links to. This is useful when the ordering of edges has been changed, fn correct_parent_link(self) { // Create backpointer without invalidating other references to the node. let ptr = unsafe { NonNull::new_unchecked(NodeRef::as_internal_ptr(&self.node)) }; @@ -1009,8 +1019,8 @@ impl<'a, K, V> Handle, K, V, marker::Internal>, marker:: } impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Internal>, marker::Edge> { - /// Inserts a new key/value pair and an edge that will go to the right of that new pair - /// between this edge and the key/value pair to the right of this edge. This method assumes + /// Inserts a new key-value pair and an edge that will go to the right of that new pair + /// between this edge and the key-value pair to the right of this edge. This method assumes /// that there is enough space in the node for the new pair to fit. fn insert_fit(&mut self, key: K, val: V, edge: Root) { debug_assert!(self.node.len() < CAPACITY); @@ -1026,8 +1036,8 @@ impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Internal>, } } - /// Inserts a new key/value pair and an edge that will go to the right of that new pair - /// between this edge and the key/value pair to the right of this edge. This method splits + /// Inserts a new key-value pair and an edge that will go to the right of that new pair + /// between this edge and the key-value pair to the right of this edge. This method splits /// the node if there isn't enough room. fn insert( mut self, @@ -1060,7 +1070,7 @@ impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Internal>, } impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Leaf>, marker::Edge> { - /// Inserts a new key/value pair between the key/value pairs to the right and left of + /// Inserts a new key-value pair between the key-value pairs to the right and left of /// this edge. This method splits the node if there isn't enough room, and tries to /// insert the split off portion into the parent node recursively, until the root is reached. /// @@ -1098,6 +1108,8 @@ impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Leaf>, mark impl Handle, marker::Edge> { /// Finds the node pointed to by this edge. /// + /// The method name assumes you picture trees with the root node on top. + /// /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should /// both, upon success, do nothing. pub fn descend(self) -> NodeRef { @@ -1186,10 +1198,10 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle, K, V, NodeType> impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Leaf>, marker::KV> { /// Splits the underlying node into three parts: /// - /// - The node is truncated to only contain the key/value pairs to the left of + /// - The node is truncated to only contain the key-value pairs to the left of /// this handle. /// - The key and value pointed to by this handle are extracted. - /// - All the key/value pairs to the right of this handle are put into a newly + /// - All the key-value pairs to the right of this handle are put into a newly /// allocated node. pub fn split(mut self) -> SplitResult<'a, K, V, marker::Leaf> { unsafe { @@ -1202,8 +1214,8 @@ impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Leaf>, mark } } - /// Removes the key/value pair pointed to by this handle and returns it, along with the edge - /// that the key/value pair collapsed into. + /// Removes the key-value pair pointed to by this handle and returns it, along with the edge + /// that the key-value pair collapsed into. pub fn remove( mut self, ) -> ((K, V), Handle, K, V, marker::Leaf>, marker::Edge>) { @@ -1219,10 +1231,10 @@ impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Leaf>, mark impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Internal>, marker::KV> { /// Splits the underlying node into three parts: /// - /// - The node is truncated to only contain the edges and key/value pairs to the + /// - The node is truncated to only contain the edges and key-value pairs to the /// left of this handle. /// - The key and value pointed to by this handle are extracted. - /// - All the edges and key/value pairs to the right of this handle are put into + /// - All the edges and key-value pairs to the right of this handle are put into /// a newly allocated node. pub fn split(mut self) -> SplitResult<'a, K, V, marker::Internal> { unsafe { @@ -1247,7 +1259,7 @@ impl<'a, K: 'a, V: 'a> Handle, K, V, marker::Internal>, } /// Represents a session for evaluating and performing a balancing operation -/// around an internal key/value pair. +/// around an internal key-value pair. pub struct BalancingContext<'a, K, V> { parent: Handle, K, V, marker::Internal>, marker::KV>, left_child: NodeRef, K, V, marker::LeafOrInternal>, @@ -1320,14 +1332,14 @@ impl<'a, K, V> BalancingContext<'a, K, V> { /// Returns `true` if it is valid to call `.merge()` in the balancing context, /// i.e., whether there is enough room in a node to hold the combination of - /// both adjacent child nodes, along with the key/value pair in the parent. + /// both adjacent child nodes, along with the key-value pair in the parent. pub fn can_merge(&self) -> bool { self.left_child.len() + 1 + self.right_child.len() <= CAPACITY } } impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> { - /// Merges the parent's key/value pair and both adjacent child nodes into + /// Merges the parent's key-value pair and both adjacent child nodes into /// the left node and returns an edge handle in that expanded left node. /// If `track_edge_idx` is given some value, the returned edge corresponds /// to where the edge in that child node ended up, @@ -1409,8 +1421,8 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> { } } - /// Removes a key/value pair from the left child and places it in the key/value storage - /// of the parent, while pushing the old parent key/value pair into the right child. + /// Removes a key-value pair from the left child and places it in the key-value storage + /// of the parent, while pushing the old parent key-value pair into the right child. /// Returns a handle to the edge in the right child corresponding to where the original /// edge specified by `track_right_edge_idx` ended up. pub fn steal_left( @@ -1432,8 +1444,8 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> { } } - /// Removes a key/value pair from the right child and places it in the key/value storage - /// of the parent, while pushing the old parent key/value pair onto the left child. + /// Removes a key-value pair from the right child and places it in the key-value storage + /// of the parent, while pushing the old parent key-value pair onto the left child. /// Returns a handle to the edge in the left child specified by `track_left_edge_idx`, /// which didn't move. pub fn steal_right( @@ -1459,17 +1471,17 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> { pub fn bulk_steal_left(&mut self, count: usize) { unsafe { let left_node = &mut self.left_child; - let left_len = left_node.len(); + let old_left_len = left_node.len(); let right_node = &mut self.right_child; - let right_len = right_node.len(); + let old_right_len = right_node.len(); // Make sure that we may steal safely. - assert!(right_len + count <= CAPACITY); - assert!(left_len >= count); + assert!(old_right_len + count <= CAPACITY); + assert!(old_left_len >= count); - let new_left_len = left_len - count; + let new_left_len = old_left_len - count; - // Move data. + // Move leaf data. { let left_kv = left_node.reborrow_mut().into_kv_pointers_mut(); let right_kv = right_node.reborrow_mut().into_kv_pointers_mut(); @@ -1479,13 +1491,13 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> { }; // Make room for stolen elements in the right child. - ptr::copy(right_kv.0, right_kv.0.add(count), right_len); - ptr::copy(right_kv.1, right_kv.1.add(count), right_len); + ptr::copy(right_kv.0, right_kv.0.add(count), old_right_len); + ptr::copy(right_kv.1, right_kv.1.add(count), old_right_len); // Move elements from the left child to the right one. move_kv(left_kv, new_left_len + 1, right_kv, 0, count - 1); - // Move parent's key/value pair to the right child. + // Move parent's key-value pair to the right child. move_kv(parent_kv, 0, right_kv, count - 1, 1); // Move the left-most stolen pair to the parent. @@ -1500,9 +1512,10 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> { // Make room for stolen edges. let left = left.reborrow(); let right_edges = right.reborrow_mut().into_edge_area_slice().as_mut_ptr(); - ptr::copy(right_edges, right_edges.add(count), right_len + 1); - right.correct_childrens_parent_links(count..count + right_len + 1); + ptr::copy(right_edges, right_edges.add(count), old_right_len + 1); + right.correct_childrens_parent_links(count..count + old_right_len + 1); + // Steal edges. move_edges(left, new_left_len + 1, right, 0, count); } (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {} @@ -1515,17 +1528,17 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> { pub fn bulk_steal_right(&mut self, count: usize) { unsafe { let left_node = &mut self.left_child; - let left_len = left_node.len(); + let old_left_len = left_node.len(); let right_node = &mut self.right_child; - let right_len = right_node.len(); + let old_right_len = right_node.len(); // Make sure that we may steal safely. - assert!(left_len + count <= CAPACITY); - assert!(right_len >= count); + assert!(old_left_len + count <= CAPACITY); + assert!(old_right_len >= count); - let new_right_len = right_len - count; + let new_right_len = old_right_len - count; - // Move data. + // Move leaf data. { let left_kv = left_node.reborrow_mut().into_kv_pointers_mut(); let right_kv = right_node.reborrow_mut().into_kv_pointers_mut(); @@ -1534,16 +1547,16 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> { (kv.0 as *mut K, kv.1 as *mut V) }; - // Move parent's key/value pair to the left child. - move_kv(parent_kv, 0, left_kv, left_len, 1); + // Move parent's key-value pair to the left child. + move_kv(parent_kv, 0, left_kv, old_left_len, 1); // Move elements from the right child to the left one. - move_kv(right_kv, 0, left_kv, left_len + 1, count - 1); + move_kv(right_kv, 0, left_kv, old_left_len + 1, count - 1); // Move the right-most stolen pair to the parent. move_kv(right_kv, count - 1, parent_kv, 0, 1); - // Fix right indexing + // Fill gap where stolen elements used to be. ptr::copy(right_kv.0.add(count), right_kv.0, new_right_len); ptr::copy(right_kv.1.add(count), right_kv.1, new_right_len); } @@ -1553,9 +1566,10 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> { match (left_node.reborrow_mut().force(), right_node.reborrow_mut().force()) { (ForceResult::Internal(left), ForceResult::Internal(mut right)) => { - move_edges(right.reborrow(), 0, left, left_len + 1, count); + // Steal edges. + move_edges(right.reborrow(), 0, left, old_left_len + 1, count); - // Fix right indexing. + // Fill gap where stolen edges used to be. let right_edges = right.reborrow_mut().into_edge_area_slice().as_mut_ptr(); ptr::copy(right_edges.add(count), right_edges, new_right_len + 1); right.correct_childrens_parent_links(0..=new_right_len); @@ -1671,28 +1685,28 @@ impl<'a, K, V> Handle, K, V, marker::LeafOrInternal>, ma right: &mut NodeRef, K, V, marker::LeafOrInternal>, ) { unsafe { - let left_new_len = self.idx; + let new_left_len = self.idx; let mut left_node = self.reborrow_mut().into_node(); - let right_new_len = left_node.len() - left_new_len; + let new_right_len = left_node.len() - new_left_len; let mut right_node = right.reborrow_mut(); assert!(right_node.len() == 0); assert!(left_node.height == right_node.height); - if right_new_len > 0 { + if new_right_len > 0 { let left_kv = left_node.reborrow_mut().into_kv_pointers_mut(); let right_kv = right_node.reborrow_mut().into_kv_pointers_mut(); - move_kv(left_kv, left_new_len, right_kv, 0, right_new_len); + move_kv(left_kv, new_left_len, right_kv, 0, new_right_len); - *left_node.reborrow_mut().into_len_mut() = left_new_len as u16; - *right_node.reborrow_mut().into_len_mut() = right_new_len as u16; + *left_node.reborrow_mut().into_len_mut() = new_left_len as u16; + *right_node.reborrow_mut().into_len_mut() = new_right_len as u16; match (left_node.force(), right_node.force()) { (ForceResult::Internal(left), ForceResult::Internal(right)) => { let left = left.reborrow(); - move_edges(left, left_new_len + 1, right, 1, right_new_len); + move_edges(left, new_left_len + 1, right, 1, new_right_len); } (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {} _ => unreachable!(), diff --git a/library/alloc/src/collections/btree/remove.rs b/library/alloc/src/collections/btree/remove.rs index c4253d4221b3b..5ae1c1fcab803 100644 --- a/library/alloc/src/collections/btree/remove.rs +++ b/library/alloc/src/collections/btree/remove.rs @@ -4,7 +4,7 @@ use super::unwrap_unchecked; use core::mem; impl<'a, K: 'a, V: 'a> Handle, K, V, marker::LeafOrInternal>, marker::KV> { - /// Removes a key/value-pair from the tree, and returns that pair, as well as + /// Removes a key-value pair from the tree, and returns that pair, as well as /// the leaf edge corresponding to that former pair. It's possible this empties /// a root node that is internal, which the caller should pop from the map /// holding the tree. The caller should also decrement the map's length. diff --git a/library/alloc/src/collections/btree/search.rs b/library/alloc/src/collections/btree/search.rs index 93de2d829ac8d..ed7f95fe632fa 100644 --- a/library/alloc/src/collections/btree/search.rs +++ b/library/alloc/src/collections/btree/search.rs @@ -14,6 +14,9 @@ pub enum SearchResult { /// Returns a `Found` with the handle of the matching KV, if any. Otherwise, /// returns a `GoDown` with the handle of the possible leaf edge where the key /// belongs. +/// +/// The result is meaningful only if the tree is ordered by key, like the tree +/// in a `BTreeMap` is. pub fn search_tree( mut node: NodeRef, key: &Q, @@ -38,8 +41,11 @@ where /// Looks up a given key in a given node, without recursion. /// Returns a `Found` with the handle of the matching KV, if any. Otherwise, -/// returns a `GoDown` with the handle of the edge where the key might be found. -/// If the node is a leaf, a `GoDown` edge is not an actual edge but a possible edge. +/// returns a `GoDown` with the handle of the edge where the key might be found +/// (if the node is internal) or where the key can be inserted. +/// +/// The result is meaningful only if the tree is ordered by key, like the tree +/// in a `BTreeMap` is. pub fn search_node( node: NodeRef, key: &Q, @@ -54,11 +60,11 @@ where } } -/// Returns the index in the node at which the key (or an equivalent) exists -/// or could exist, and whether it exists in the node itself. If it doesn't -/// exist in the node itself, it may exist in the subtree with that index -/// (if the node has subtrees). If the key doesn't exist in node or subtree, -/// the returned index is the position or subtree where the key belongs. +/// Returns either the KV index in the node at which the key (or an equivalent) +/// exists and `true`, or the edge index where the key belongs and `false`. +/// +/// The result is meaningful only if the tree is ordered by key, like the tree +/// in a `BTreeMap` is. fn search_linear( node: &NodeRef, key: &Q, diff --git a/library/alloc/src/collections/btree/set.rs b/library/alloc/src/collections/btree/set.rs index f4046e87b99a8..d8ce47ed77d1f 100644 --- a/library/alloc/src/collections/btree/set.rs +++ b/library/alloc/src/collections/btree/set.rs @@ -214,7 +214,7 @@ impl fmt::Debug for Union<'_, T> { // This constant is used by functions that compare two sets. // It estimates the relative size at which searching performs better // than iterating, based on the benchmarks in -// https://github.com/ssomers/rust_bench_btreeset_intersection; +// https://github.com/ssomers/rust_bench_btreeset_intersection. // It's used to divide rather than multiply sizes, to rule out overflow, // and it's a power of two to make that division cheap. const ITER_PERFORMANCE_TIPPING_SIZE_DIFF: usize = 16; diff --git a/library/alloc/src/collections/btree/split.rs b/library/alloc/src/collections/btree/split.rs index 701f36c37ee88..6108c139bb3a6 100644 --- a/library/alloc/src/collections/btree/split.rs +++ b/library/alloc/src/collections/btree/split.rs @@ -23,8 +23,8 @@ impl Root { loop { let mut split_edge = match search_node(left_node, key) { // key is going to the right tree - Found(handle) => handle.left_edge(), - GoDown(handle) => handle, + Found(kv) => kv.left_edge(), + GoDown(edge) => edge, }; split_edge.move_suffix(&mut right_node);