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BTreeMap: admit the existence of leaf edges in comments

This commit is contained in:
Stein Somers 2020-08-09 12:25:20 +02:00
parent fc42fb8e70
commit df76cf89ad
1 changed files with 12 additions and 22 deletions
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34
library/alloc/src/collections/btree/node.rs
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@ -9,11 +9,8 @@
// struct Node<K, V, height: usize> { // struct Node<K, V, height: usize> {
// keys: [K; 2 * B - 1], // keys: [K; 2 * B - 1],
// vals: [V; 2 * B - 1], // vals: [V; 2 * B - 1],
// edges: if height > 0 { // edges: [if height > 0 { Box<Node<K, V, height - 1>> } else { () }; 2 * B],
// [Box<Node<K, V, height - 1>>; 2 * B] // parent: Option<(NonNull<Node<K, V, height + 1>>, u16)>,
// } else { () },
// parent: Option<NonNull<Node<K, V, height + 1>>>,
// parent_idx: u16,
// len: u16, // len: u16,
// } // }
// ``` // ```
@ -28,8 +25,8 @@
// //
// - Trees must have uniform depth/height. This means that every path down to a leaf from a // - Trees must have uniform depth/height. This means that every path down to a leaf from a
// given node has exactly the same length. // given node has exactly the same length.
// - A node of length `n` has `n` keys, `n` values, and (in an internal node) `n + 1` edges. // - A node of length `n` has `n` keys, `n` values, and `n + 1` edges.
// This implies that even an empty internal node has at least one edge. // This implies that even an empty node has at least one edge.
use core::cmp::Ordering; use core::cmp::Ordering;
use core::marker::PhantomData; use core::marker::PhantomData;
@ -298,9 +295,8 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
} }
impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> { impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
/// Finds the length of the node. This is the number of keys or values. In an /// Finds the length of the node. This is the number of keys or values.
/// internal node, the number of edges is `len() + 1`. /// The number of edges is `len() + 1`.
/// For any node, the number of possible edge handles is also `len() + 1`.
/// Note that, despite being safe, calling this function can have the side effect /// Note that, despite being safe, calling this function can have the side effect
/// of invalidating mutable references that unsafe code has created. /// of invalidating mutable references that unsafe code has created.
pub fn len(&self) -> usize { pub fn len(&self) -> usize {
@ -321,9 +317,6 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
} }
/// Exposes the leaf portion of any leaf or internal node. /// Exposes the leaf portion of any leaf or internal node.
/// If the node is a leaf, this function simply opens up its data.
/// If the node is an internal node, so not a leaf, it does have all the data a leaf has
/// (header, keys and values), and this function exposes that.
/// ///
/// Returns a raw ptr to avoid invalidating other references to this node, /// Returns a raw ptr to avoid invalidating other references to this node,
/// which is possible when BorrowType is marker::ValMut. /// which is possible when BorrowType is marker::ValMut.
@ -471,9 +464,6 @@ impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
} }
/// Exposes the leaf portion of any leaf or internal node for writing. /// Exposes the leaf portion of any leaf or internal node for writing.
/// If the node is a leaf, this function simply opens up its data.
/// If the node is an internal node, so not a leaf, it does have all the data a leaf has
/// (header, keys and values), and this function exposes that.
/// ///
/// We don't need to return a raw ptr because we have unique access to the entire node. /// We don't need to return a raw ptr because we have unique access to the entire node.
fn as_leaf_mut(&mut self) -> &'a mut LeafNode<K, V> { fn as_leaf_mut(&mut self) -> &'a mut LeafNode<K, V> {
@ -679,9 +669,9 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
} }
impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> { impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
/// Removes a key/value pair from the end of this node and returns the pair. /// Removes a key/value pair from the end of the node and returns the pair.
/// If this is an internal node, also removes the edge that was to the right /// Also removes the edge that was to the right of that pair and, if the node
/// of that pair and returns the orphaned node that this edge owned. /// is internal, returns the orphaned subtree that this edge owned.
fn pop(&mut self) -> (K, V, Option<Root<K, V>>) { fn pop(&mut self) -> (K, V, Option<Root<K, V>>) {
debug_assert!(self.len() > 0); debug_assert!(self.len() > 0);
@ -705,9 +695,9 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
} }
} }
/// Removes a key/value pair from the beginning of this node and returns the pair. /// Removes a key/value pair from the beginning of the node and returns the pair.
/// If this is an internal node, also removes the edge that was to the left /// Also removes the edge that was to the left of that pair and, if the node is
/// of that pair and returns the orphaned node that this edge owned. /// internal, returns the orphaned subtree that this edge owned.
fn pop_front(&mut self) -> (K, V, Option<Root<K, V>>) { fn pop_front(&mut self) -> (K, V, Option<Root<K, V>>) {
debug_assert!(self.len() > 0); debug_assert!(self.len() > 0);