1 // This is an attempt at an implementation following the ideal
4 // struct BTreeMap<K, V> {
6 // root: Option<Box<Node<K, V, height>>>
9 // struct Node<K, V, height: usize> {
10 // keys: [K; 2 * B - 1],
11 // vals: [V; 2 * B - 1],
12 // edges: [if height > 0 { Box<Node<K, V, height - 1>> } else { () }; 2 * B],
13 // parent: Option<(NonNull<Node<K, V, height + 1>>, u16)>,
18 // Since Rust doesn't actually have dependent types and polymorphic recursion,
19 // we make do with lots of unsafety.
21 // A major goal of this module is to avoid complexity by treating the tree as a generic (if
22 // weirdly shaped) container and avoiding dealing with most of the B-Tree invariants. As such,
23 // this module doesn't care whether the entries are sorted, which nodes can be underfull, or
24 // even what underfull means. However, we do rely on a few invariants:
26 // - Trees must have uniform depth/height. This means that every path down to a leaf from a
27 // given node has exactly the same length.
28 // - A node of length `n` has `n` keys, `n` values, and `n + 1` edges.
29 // This implies that even an empty node has at least one edge.
30 // For a leaf node, "having an edge" only means we can identify a position in the node,
31 // since leaf edges are empty and need no data representation. In an internal node,
32 // an edge both identifies a position and contains a pointer to a child node.
34 use core::marker::PhantomData;
35 use core::mem::{self, MaybeUninit};
36 use core::ptr::{self, NonNull};
37 use core::slice::SliceIndex;
39 use crate::alloc::{Allocator, Global, Layout};
40 use crate::boxed::Box;
43 pub const CAPACITY: usize = 2 * B - 1;
44 pub const MIN_LEN_AFTER_SPLIT: usize = B - 1;
45 const KV_IDX_CENTER: usize = B - 1;
46 const EDGE_IDX_LEFT_OF_CENTER: usize = B - 1;
47 const EDGE_IDX_RIGHT_OF_CENTER: usize = B;
49 /// The underlying representation of leaf nodes and part of the representation of internal nodes.
50 struct LeafNode<K, V> {
51 /// We want to be covariant in `K` and `V`.
52 parent: Option<NonNull<InternalNode<K, V>>>,
54 /// This node's index into the parent node's `edges` array.
55 /// `*node.parent.edges[node.parent_idx]` should be the same thing as `node`.
56 /// This is only guaranteed to be initialized when `parent` is non-null.
57 parent_idx: MaybeUninit<u16>,
59 /// The number of keys and values this node stores.
62 /// The arrays storing the actual data of the node. Only the first `len` elements of each
63 /// array are initialized and valid.
64 keys: [MaybeUninit<K>; CAPACITY],
65 vals: [MaybeUninit<V>; CAPACITY],
68 impl<K, V> LeafNode<K, V> {
69 /// Initializes a new `LeafNode` in-place.
70 unsafe fn init(this: *mut Self) {
71 // As a general policy, we leave fields uninitialized if they can be, as this should
72 // be both slightly faster and easier to track in Valgrind.
74 // parent_idx, keys, and vals are all MaybeUninit
75 ptr::addr_of_mut!((*this).parent).write(None);
76 ptr::addr_of_mut!((*this).len).write(0);
80 /// Creates a new boxed `LeafNode`.
81 fn new() -> Box<Self> {
83 let mut leaf = Box::new_uninit();
84 LeafNode::init(leaf.as_mut_ptr());
90 /// The underlying representation of internal nodes. As with `LeafNode`s, these should be hidden
91 /// behind `BoxedNode`s to prevent dropping uninitialized keys and values. Any pointer to an
92 /// `InternalNode` can be directly cast to a pointer to the underlying `LeafNode` portion of the
93 /// node, allowing code to act on leaf and internal nodes generically without having to even check
94 /// which of the two a pointer is pointing at. This property is enabled by the use of `repr(C)`.
96 // gdb_providers.py uses this type name for introspection.
97 struct InternalNode<K, V> {
100 /// The pointers to the children of this node. `len + 1` of these are considered
101 /// initialized and valid, except that near the end, while the tree is held
102 /// through borrow type `Dying`, some of these pointers are dangling.
103 edges: [MaybeUninit<BoxedNode<K, V>>; 2 * B],
106 impl<K, V> InternalNode<K, V> {
107 /// Creates a new boxed `InternalNode`.
110 /// An invariant of internal nodes is that they have at least one
111 /// initialized and valid edge. This function does not set up
113 unsafe fn new() -> Box<Self> {
115 let mut node = Box::<Self>::new_uninit();
116 // We only need to initialize the data; the edges are MaybeUninit.
117 LeafNode::init(ptr::addr_of_mut!((*node.as_mut_ptr()).data));
123 /// A managed, non-null pointer to a node. This is either an owned pointer to
124 /// `LeafNode<K, V>` or an owned pointer to `InternalNode<K, V>`.
126 /// However, `BoxedNode` contains no information as to which of the two types
127 /// of nodes it actually contains, and, partially due to this lack of information,
128 /// is not a separate type and has no destructor.
129 type BoxedNode<K, V> = NonNull<LeafNode<K, V>>;
131 // N.B. `NodeRef` is always covariant in `K` and `V`, even when the `BorrowType`
132 // is `Mut`. This is technically wrong, but cannot result in any unsafety due to
133 // internal use of `NodeRef` because we stay completely generic over `K` and `V`.
134 // However, whenever a public type wraps `NodeRef`, make sure that it has the
137 /// A reference to a node.
139 /// This type has a number of parameters that controls how it acts:
140 /// - `BorrowType`: A dummy type that describes the kind of borrow and carries a lifetime.
141 /// - When this is `Immut<'a>`, the `NodeRef` acts roughly like `&'a Node`.
142 /// - When this is `ValMut<'a>`, the `NodeRef` acts roughly like `&'a Node`
143 /// with respect to keys and tree structure, but also allows many
144 /// mutable references to values throughout the tree to coexist.
145 /// - When this is `Mut<'a>`, the `NodeRef` acts roughly like `&'a mut Node`,
146 /// although insert methods allow a mutable pointer to a value to coexist.
147 /// - When this is `Owned`, the `NodeRef` acts roughly like `Box<Node>`,
148 /// but does not have a destructor, and must be cleaned up manually.
149 /// - When this is `Dying`, the `NodeRef` still acts roughly like `Box<Node>`,
150 /// but has methods to destroy the tree bit by bit, and ordinary methods,
151 /// while not marked as unsafe to call, can invoke UB if called incorrectly.
152 /// Since any `NodeRef` allows navigating through the tree, `BorrowType`
153 /// effectively applies to the entire tree, not just to the node itself.
154 /// - `K` and `V`: These are the types of keys and values stored in the nodes.
155 /// - `Type`: This can be `Leaf`, `Internal`, or `LeafOrInternal`. When this is
156 /// `Leaf`, the `NodeRef` points to a leaf node, when this is `Internal` the
157 /// `NodeRef` points to an internal node, and when this is `LeafOrInternal` the
158 /// `NodeRef` could be pointing to either type of node.
159 /// `Type` is named `NodeType` when used outside `NodeRef`.
161 /// Both `BorrowType` and `NodeType` restrict what methods we implement, to
162 /// exploit static type safety. There are limitations in the way we can apply
163 /// such restrictions:
164 /// - For each type parameter, we can only define a method either generically
165 /// or for one particular type. For example, we cannot define a method like
166 /// `into_kv` generically for all `BorrowType`, or once for all types that
167 /// carry a lifetime, because we want it to return `&'a` references.
168 /// Therefore, we define it only for the least powerful type `Immut<'a>`.
169 /// - We cannot get implicit coercion from say `Mut<'a>` to `Immut<'a>`.
170 /// Therefore, we have to explicitly call `reborrow` on a more powerful
171 /// `NodeRef` in order to reach a method like `into_kv`.
173 /// All methods on `NodeRef` that return some kind of reference, either:
174 /// - Take `self` by value, and return the lifetime carried by `BorrowType`.
175 /// Sometimes, to invoke such a method, we need to call `reborrow_mut`.
176 /// - Take `self` by reference, and (implicitly) return that reference's
177 /// lifetime, instead of the lifetime carried by `BorrowType`. That way,
178 /// the borrow checker guarantees that the `NodeRef` remains borrowed as long
179 /// as the returned reference is used.
180 /// The methods supporting insert bend this rule by returning a raw pointer,
181 /// i.e., a reference without any lifetime.
182 pub struct NodeRef<BorrowType, K, V, Type> {
183 /// The number of levels that the node and the level of leaves are apart, a
184 /// constant of the node that cannot be entirely described by `Type`, and that
185 /// the node itself does not store. We only need to store the height of the root
186 /// node, and derive every other node's height from it.
187 /// Must be zero if `Type` is `Leaf` and non-zero if `Type` is `Internal`.
189 /// The pointer to the leaf or internal node. The definition of `InternalNode`
190 /// ensures that the pointer is valid either way.
191 node: NonNull<LeafNode<K, V>>,
192 _marker: PhantomData<(BorrowType, Type)>,
195 /// The root node of an owned tree.
197 /// Note that this does not have a destructor, and must be cleaned up manually.
198 pub type Root<K, V> = NodeRef<marker::Owned, K, V, marker::LeafOrInternal>;
200 impl<'a, K: 'a, V: 'a, Type> Copy for NodeRef<marker::Immut<'a>, K, V, Type> {}
201 impl<'a, K: 'a, V: 'a, Type> Clone for NodeRef<marker::Immut<'a>, K, V, Type> {
202 fn clone(&self) -> Self {
207 unsafe impl<BorrowType, K: Sync, V: Sync, Type> Sync for NodeRef<BorrowType, K, V, Type> {}
209 unsafe impl<'a, K: Sync + 'a, V: Sync + 'a, Type> Send for NodeRef<marker::Immut<'a>, K, V, Type> {}
210 unsafe impl<'a, K: Send + 'a, V: Send + 'a, Type> Send for NodeRef<marker::Mut<'a>, K, V, Type> {}
211 unsafe impl<'a, K: Send + 'a, V: Send + 'a, Type> Send for NodeRef<marker::ValMut<'a>, K, V, Type> {}
212 unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Owned, K, V, Type> {}
213 unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Dying, K, V, Type> {}
215 impl<K, V> NodeRef<marker::Owned, K, V, marker::Leaf> {
216 pub fn new_leaf() -> Self {
217 Self::from_new_leaf(LeafNode::new())
220 fn from_new_leaf(leaf: Box<LeafNode<K, V>>) -> Self {
221 NodeRef { height: 0, node: NonNull::from(Box::leak(leaf)), _marker: PhantomData }
225 impl<K, V> NodeRef<marker::Owned, K, V, marker::Internal> {
226 fn new_internal(child: Root<K, V>) -> Self {
227 let mut new_node = unsafe { InternalNode::new() };
228 new_node.edges[0].write(child.node);
229 unsafe { NodeRef::from_new_internal(new_node, child.height + 1) }
233 /// `height` must not be zero.
234 unsafe fn from_new_internal(internal: Box<InternalNode<K, V>>, height: usize) -> Self {
235 debug_assert!(height > 0);
236 let node = NonNull::from(Box::leak(internal)).cast();
237 let mut this = NodeRef { height, node, _marker: PhantomData };
238 this.borrow_mut().correct_all_childrens_parent_links();
243 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
244 /// Unpack a node reference that was packed as `NodeRef::parent`.
245 fn from_internal(node: NonNull<InternalNode<K, V>>, height: usize) -> Self {
246 debug_assert!(height > 0);
247 NodeRef { height, node: node.cast(), _marker: PhantomData }
251 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
252 /// Exposes the data of an internal node.
254 /// Returns a raw ptr to avoid invalidating other references to this node.
255 fn as_internal_ptr(this: &Self) -> *mut InternalNode<K, V> {
256 // SAFETY: the static node type is `Internal`.
257 this.node.as_ptr() as *mut InternalNode<K, V>
261 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
262 /// Borrows exclusive access to the data of an internal node.
263 fn as_internal_mut(&mut self) -> &mut InternalNode<K, V> {
264 let ptr = Self::as_internal_ptr(self);
269 impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
270 /// Finds the length of the node. This is the number of keys or values.
271 /// The number of edges is `len() + 1`.
272 /// Note that, despite being safe, calling this function can have the side effect
273 /// of invalidating mutable references that unsafe code has created.
274 pub fn len(&self) -> usize {
275 // Crucially, we only access the `len` field here. If BorrowType is marker::ValMut,
276 // there might be outstanding mutable references to values that we must not invalidate.
277 unsafe { usize::from((*Self::as_leaf_ptr(self)).len) }
280 /// Returns the number of levels that the node and leaves are apart. Zero
281 /// height means the node is a leaf itself. If you picture trees with the
282 /// root on top, the number says at which elevation the node appears.
283 /// If you picture trees with leaves on top, the number says how high
284 /// the tree extends above the node.
285 pub fn height(&self) -> usize {
289 /// Temporarily takes out another, immutable reference to the same node.
290 pub fn reborrow(&self) -> NodeRef<marker::Immut<'_>, K, V, Type> {
291 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
294 /// Exposes the leaf portion of any leaf or internal node.
296 /// Returns a raw ptr to avoid invalidating other references to this node.
297 fn as_leaf_ptr(this: &Self) -> *mut LeafNode<K, V> {
298 // The node must be valid for at least the LeafNode portion.
299 // This is not a reference in the NodeRef type because we don't know if
300 // it should be unique or shared.
305 impl<BorrowType: marker::BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
306 /// Finds the parent of the current node. Returns `Ok(handle)` if the current
307 /// node actually has a parent, where `handle` points to the edge of the parent
308 /// that points to the current node. Returns `Err(self)` if the current node has
309 /// no parent, giving back the original `NodeRef`.
311 /// The method name assumes you picture trees with the root node on top.
313 /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
314 /// both, upon success, do nothing.
317 ) -> Result<Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>, Self> {
318 assert!(BorrowType::PERMITS_TRAVERSAL);
319 // We need to use raw pointers to nodes because, if BorrowType is marker::ValMut,
320 // there might be outstanding mutable references to values that we must not invalidate.
321 let leaf_ptr: *const _ = Self::as_leaf_ptr(&self);
322 unsafe { (*leaf_ptr).parent }
324 .map(|parent| Handle {
325 node: NodeRef::from_internal(*parent, self.height + 1),
326 idx: unsafe { usize::from((*leaf_ptr).parent_idx.assume_init()) },
327 _marker: PhantomData,
332 pub fn first_edge(self) -> Handle<Self, marker::Edge> {
333 unsafe { Handle::new_edge(self, 0) }
336 pub fn last_edge(self) -> Handle<Self, marker::Edge> {
337 let len = self.len();
338 unsafe { Handle::new_edge(self, len) }
341 /// Note that `self` must be nonempty.
342 pub fn first_kv(self) -> Handle<Self, marker::KV> {
343 let len = self.len();
345 unsafe { Handle::new_kv(self, 0) }
348 /// Note that `self` must be nonempty.
349 pub fn last_kv(self) -> Handle<Self, marker::KV> {
350 let len = self.len();
352 unsafe { Handle::new_kv(self, len - 1) }
356 impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
357 /// Could be a public implementation of PartialEq, but only used in this module.
358 fn eq(&self, other: &Self) -> bool {
359 let Self { node, height, _marker } = self;
360 if node.eq(&other.node) {
361 debug_assert_eq!(*height, other.height);
369 impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
370 /// Exposes the leaf portion of any leaf or internal node in an immutable tree.
371 fn into_leaf(self) -> &'a LeafNode<K, V> {
372 let ptr = Self::as_leaf_ptr(&self);
373 // SAFETY: there can be no mutable references into this tree borrowed as `Immut`.
377 /// Borrows a view into the keys stored in the node.
378 pub fn keys(&self) -> &[K] {
379 let leaf = self.into_leaf();
381 MaybeUninit::slice_assume_init_ref(leaf.keys.get_unchecked(..usize::from(leaf.len)))
386 impl<K, V> NodeRef<marker::Dying, K, V, marker::LeafOrInternal> {
387 /// Similar to `ascend`, gets a reference to a node's parent node, but also
388 /// deallocates the current node in the process. This is unsafe because the
389 /// current node will still be accessible despite being deallocated.
390 pub unsafe fn deallocate_and_ascend(
392 ) -> Option<Handle<NodeRef<marker::Dying, K, V, marker::Internal>, marker::Edge>> {
393 let height = self.height;
394 let node = self.node;
395 let ret = self.ascend().ok();
400 Layout::new::<InternalNode<K, V>>()
402 Layout::new::<LeafNode<K, V>>()
410 impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
411 /// Temporarily takes out another mutable reference to the same node. Beware, as
412 /// this method is very dangerous, doubly so since it might not immediately appear
415 /// Because mutable pointers can roam anywhere around the tree, the returned
416 /// pointer can easily be used to make the original pointer dangling, out of
417 /// bounds, or invalid under stacked borrow rules.
418 // FIXME(@gereeter) consider adding yet another type parameter to `NodeRef`
419 // that restricts the use of navigation methods on reborrowed pointers,
420 // preventing this unsafety.
421 unsafe fn reborrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
422 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
425 /// Borrows exclusive access to the leaf portion of a leaf or internal node.
426 fn as_leaf_mut(&mut self) -> &mut LeafNode<K, V> {
427 let ptr = Self::as_leaf_ptr(self);
428 // SAFETY: we have exclusive access to the entire node.
432 /// Offers exclusive access to the leaf portion of a leaf or internal node.
433 fn into_leaf_mut(mut self) -> &'a mut LeafNode<K, V> {
434 let ptr = Self::as_leaf_ptr(&mut self);
435 // SAFETY: we have exclusive access to the entire node.
440 impl<K, V, Type> NodeRef<marker::Dying, K, V, Type> {
441 /// Borrows exclusive access to the leaf portion of a dying leaf or internal node.
442 fn as_leaf_dying(&mut self) -> &mut LeafNode<K, V> {
443 let ptr = Self::as_leaf_ptr(self);
444 // SAFETY: we have exclusive access to the entire node.
449 impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
450 /// Borrows exclusive access to an element of the key storage area.
453 /// `index` is in bounds of 0..CAPACITY
454 unsafe fn key_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
456 I: SliceIndex<[MaybeUninit<K>], Output = Output>,
458 // SAFETY: the caller will not be able to call further methods on self
459 // until the key slice reference is dropped, as we have unique access
460 // for the lifetime of the borrow.
461 unsafe { self.as_leaf_mut().keys.as_mut_slice().get_unchecked_mut(index) }
464 /// Borrows exclusive access to an element or slice of the node's value storage area.
467 /// `index` is in bounds of 0..CAPACITY
468 unsafe fn val_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
470 I: SliceIndex<[MaybeUninit<V>], Output = Output>,
472 // SAFETY: the caller will not be able to call further methods on self
473 // until the value slice reference is dropped, as we have unique access
474 // for the lifetime of the borrow.
475 unsafe { self.as_leaf_mut().vals.as_mut_slice().get_unchecked_mut(index) }
479 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
480 /// Borrows exclusive access to an element or slice of the node's storage area for edge contents.
483 /// `index` is in bounds of 0..CAPACITY + 1
484 unsafe fn edge_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
486 I: SliceIndex<[MaybeUninit<BoxedNode<K, V>>], Output = Output>,
488 // SAFETY: the caller will not be able to call further methods on self
489 // until the edge slice reference is dropped, as we have unique access
490 // for the lifetime of the borrow.
491 unsafe { self.as_internal_mut().edges.as_mut_slice().get_unchecked_mut(index) }
495 impl<'a, K, V, Type> NodeRef<marker::ValMut<'a>, K, V, Type> {
497 /// - The node has more than `idx` initialized elements.
498 unsafe fn into_key_val_mut_at(mut self, idx: usize) -> (&'a K, &'a mut V) {
499 // We only create a reference to the one element we are interested in,
500 // to avoid aliasing with outstanding references to other elements,
501 // in particular, those returned to the caller in earlier iterations.
502 let leaf = Self::as_leaf_ptr(&mut self);
503 let keys = unsafe { ptr::addr_of!((*leaf).keys) };
504 let vals = unsafe { ptr::addr_of_mut!((*leaf).vals) };
505 // We must coerce to unsized array pointers because of Rust issue #74679.
506 let keys: *const [_] = keys;
507 let vals: *mut [_] = vals;
508 let key = unsafe { (&*keys.get_unchecked(idx)).assume_init_ref() };
509 let val = unsafe { (&mut *vals.get_unchecked_mut(idx)).assume_init_mut() };
514 impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
515 /// Borrows exclusive access to the length of the node.
516 pub fn len_mut(&mut self) -> &mut u16 {
517 &mut self.as_leaf_mut().len
521 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
523 /// Every item returned by `range` is a valid edge index for the node.
524 unsafe fn correct_childrens_parent_links<R: Iterator<Item = usize>>(&mut self, range: R) {
526 debug_assert!(i <= self.len());
527 unsafe { Handle::new_edge(self.reborrow_mut(), i) }.correct_parent_link();
531 fn correct_all_childrens_parent_links(&mut self) {
532 let len = self.len();
533 unsafe { self.correct_childrens_parent_links(0..=len) };
537 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
538 /// Sets the node's link to its parent edge,
539 /// without invalidating other references to the node.
540 fn set_parent_link(&mut self, parent: NonNull<InternalNode<K, V>>, parent_idx: usize) {
541 let leaf = Self::as_leaf_ptr(self);
542 unsafe { (*leaf).parent = Some(parent) };
543 unsafe { (*leaf).parent_idx.write(parent_idx as u16) };
547 impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
548 /// Clears the root's link to its parent edge.
549 fn clear_parent_link(&mut self) {
550 let mut root_node = self.borrow_mut();
551 let leaf = root_node.as_leaf_mut();
556 impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
557 /// Returns a new owned tree, with its own root node that is initially empty.
558 pub fn new() -> Self {
559 NodeRef::new_leaf().forget_type()
562 /// Adds a new internal node with a single edge pointing to the previous root node,
563 /// make that new node the root node, and return it. This increases the height by 1
564 /// and is the opposite of `pop_internal_level`.
565 pub fn push_internal_level(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::Internal> {
566 super::mem::take_mut(self, |old_root| NodeRef::new_internal(old_root).forget_type());
568 // `self.borrow_mut()`, except that we just forgot we're internal now:
569 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
572 /// Removes the internal root node, using its first child as the new root node.
573 /// As it is intended only to be called when the root node has only one child,
574 /// no cleanup is done on any of the keys, values and other children.
575 /// This decreases the height by 1 and is the opposite of `push_internal_level`.
577 /// Requires exclusive access to the `NodeRef` object but not to the root node;
578 /// it will not invalidate other handles or references to the root node.
580 /// Panics if there is no internal level, i.e., if the root node is a leaf.
581 pub fn pop_internal_level(&mut self) {
582 assert!(self.height > 0);
586 // SAFETY: we asserted to be internal.
587 let internal_self = unsafe { self.borrow_mut().cast_to_internal_unchecked() };
588 // SAFETY: we borrowed `self` exclusively and its borrow type is exclusive.
589 let internal_node = unsafe { &mut *NodeRef::as_internal_ptr(&internal_self) };
590 // SAFETY: the first edge is always initialized.
591 self.node = unsafe { internal_node.edges[0].assume_init_read() };
593 self.clear_parent_link();
596 Global.deallocate(top.cast(), Layout::new::<InternalNode<K, V>>());
601 impl<K, V, Type> NodeRef<marker::Owned, K, V, Type> {
602 /// Mutably borrows the owned root node. Unlike `reborrow_mut`, this is safe
603 /// because the return value cannot be used to destroy the root, and there
604 /// cannot be other references to the tree.
605 pub fn borrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
606 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
609 /// Slightly mutably borrows the owned root node.
610 pub fn borrow_valmut(&mut self) -> NodeRef<marker::ValMut<'_>, K, V, Type> {
611 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
614 /// Irreversibly transitions to a reference that permits traversal and offers
615 /// destructive methods and little else.
616 pub fn into_dying(self) -> NodeRef<marker::Dying, K, V, Type> {
617 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
621 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
622 /// Adds a key-value pair to the end of the node, and returns
623 /// the mutable reference of the inserted value.
624 pub fn push(&mut self, key: K, val: V) -> &mut V {
625 let len = self.len_mut();
626 let idx = usize::from(*len);
627 assert!(idx < CAPACITY);
630 self.key_area_mut(idx).write(key);
631 self.val_area_mut(idx).write(val)
636 impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
637 /// Adds a key-value pair, and an edge to go to the right of that pair,
638 /// to the end of the node.
639 pub fn push(&mut self, key: K, val: V, edge: Root<K, V>) {
640 assert!(edge.height == self.height - 1);
642 let len = self.len_mut();
643 let idx = usize::from(*len);
644 assert!(idx < CAPACITY);
647 self.key_area_mut(idx).write(key);
648 self.val_area_mut(idx).write(val);
649 self.edge_area_mut(idx + 1).write(edge.node);
650 Handle::new_edge(self.reborrow_mut(), idx + 1).correct_parent_link();
655 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Leaf> {
656 /// Removes any static information asserting that this node is a `Leaf` node.
657 pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
658 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
662 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
663 /// Removes any static information asserting that this node is an `Internal` node.
664 pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
665 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
669 impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
670 /// Checks whether a node is an `Internal` node or a `Leaf` node.
674 NodeRef<BorrowType, K, V, marker::Leaf>,
675 NodeRef<BorrowType, K, V, marker::Internal>,
677 if self.height == 0 {
678 ForceResult::Leaf(NodeRef {
681 _marker: PhantomData,
684 ForceResult::Internal(NodeRef {
687 _marker: PhantomData,
693 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
694 /// Unsafely asserts to the compiler the static information that this node is a `Leaf`.
695 unsafe fn cast_to_leaf_unchecked(self) -> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
696 debug_assert!(self.height == 0);
697 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
700 /// Unsafely asserts to the compiler the static information that this node is an `Internal`.
701 unsafe fn cast_to_internal_unchecked(self) -> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
702 debug_assert!(self.height > 0);
703 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
707 /// A reference to a specific key-value pair or edge within a node. The `Node` parameter
708 /// must be a `NodeRef`, while the `Type` can either be `KV` (signifying a handle on a key-value
709 /// pair) or `Edge` (signifying a handle on an edge).
711 /// Note that even `Leaf` nodes can have `Edge` handles. Instead of representing a pointer to
712 /// a child node, these represent the spaces where child pointers would go between the key-value
713 /// pairs. For example, in a node with length 2, there would be 3 possible edge locations - one
714 /// to the left of the node, one between the two pairs, and one at the right of the node.
715 pub struct Handle<Node, Type> {
718 _marker: PhantomData<Type>,
721 impl<Node: Copy, Type> Copy for Handle<Node, Type> {}
722 // We don't need the full generality of `#[derive(Clone)]`, as the only time `Node` will be
723 // `Clone`able is when it is an immutable reference and therefore `Copy`.
724 impl<Node: Copy, Type> Clone for Handle<Node, Type> {
725 fn clone(&self) -> Self {
730 impl<Node, Type> Handle<Node, Type> {
731 /// Retrieves the node that contains the edge or key-value pair this handle points to.
732 pub fn into_node(self) -> Node {
736 /// Returns the position of this handle in the node.
737 pub fn idx(&self) -> usize {
742 impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV> {
743 /// Creates a new handle to a key-value pair in `node`.
744 /// Unsafe because the caller must ensure that `idx < node.len()`.
745 pub unsafe fn new_kv(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
746 debug_assert!(idx < node.len());
748 Handle { node, idx, _marker: PhantomData }
751 pub fn left_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
752 unsafe { Handle::new_edge(self.node, self.idx) }
755 pub fn right_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
756 unsafe { Handle::new_edge(self.node, self.idx + 1) }
760 impl<BorrowType, K, V, NodeType, HandleType> PartialEq
761 for Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
763 fn eq(&self, other: &Self) -> bool {
764 let Self { node, idx, _marker } = self;
765 node.eq(&other.node) && *idx == other.idx
769 impl<BorrowType, K, V, NodeType, HandleType>
770 Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
772 /// Temporarily takes out another immutable handle on the same location.
773 pub fn reborrow(&self) -> Handle<NodeRef<marker::Immut<'_>, K, V, NodeType>, HandleType> {
774 // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
775 Handle { node: self.node.reborrow(), idx: self.idx, _marker: PhantomData }
779 impl<'a, K, V, NodeType, HandleType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
780 /// Temporarily takes out another mutable handle on the same location. Beware, as
781 /// this method is very dangerous, doubly so since it might not immediately appear
784 /// For details, see `NodeRef::reborrow_mut`.
785 pub unsafe fn reborrow_mut(
787 ) -> Handle<NodeRef<marker::Mut<'_>, K, V, NodeType>, HandleType> {
788 // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
789 Handle { node: unsafe { self.node.reborrow_mut() }, idx: self.idx, _marker: PhantomData }
793 impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
794 /// Creates a new handle to an edge in `node`.
795 /// Unsafe because the caller must ensure that `idx <= node.len()`.
796 pub unsafe fn new_edge(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
797 debug_assert!(idx <= node.len());
799 Handle { node, idx, _marker: PhantomData }
802 pub fn left_kv(self) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
804 Ok(unsafe { Handle::new_kv(self.node, self.idx - 1) })
810 pub fn right_kv(self) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
811 if self.idx < self.node.len() {
812 Ok(unsafe { Handle::new_kv(self.node, self.idx) })
819 pub enum LeftOrRight<T> {
824 /// Given an edge index where we want to insert into a node filled to capacity,
825 /// computes a sensible KV index of a split point and where to perform the insertion.
826 /// The goal of the split point is for its key and value to end up in a parent node;
827 /// the keys, values and edges to the left of the split point become the left child;
828 /// the keys, values and edges to the right of the split point become the right child.
829 fn splitpoint(edge_idx: usize) -> (usize, LeftOrRight<usize>) {
830 debug_assert!(edge_idx <= CAPACITY);
831 // Rust issue #74834 tries to explain these symmetric rules.
833 0..EDGE_IDX_LEFT_OF_CENTER => (KV_IDX_CENTER - 1, LeftOrRight::Left(edge_idx)),
834 EDGE_IDX_LEFT_OF_CENTER => (KV_IDX_CENTER, LeftOrRight::Left(edge_idx)),
835 EDGE_IDX_RIGHT_OF_CENTER => (KV_IDX_CENTER, LeftOrRight::Right(0)),
836 _ => (KV_IDX_CENTER + 1, LeftOrRight::Right(edge_idx - (KV_IDX_CENTER + 1 + 1))),
840 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
841 /// Inserts a new key-value pair between the key-value pairs to the right and left of
842 /// this edge. This method assumes that there is enough space in the node for the new
845 /// The returned pointer points to the inserted value.
846 fn insert_fit(&mut self, key: K, val: V) -> *mut V {
847 debug_assert!(self.node.len() < CAPACITY);
848 let new_len = self.node.len() + 1;
851 slice_insert(self.node.key_area_mut(..new_len), self.idx, key);
852 slice_insert(self.node.val_area_mut(..new_len), self.idx, val);
853 *self.node.len_mut() = new_len as u16;
855 self.node.val_area_mut(self.idx).assume_init_mut()
860 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
861 /// Inserts a new key-value pair between the key-value pairs to the right and left of
862 /// this edge. This method splits the node if there isn't enough room.
864 /// The returned pointer points to the inserted value.
865 fn insert(mut self, key: K, val: V) -> (Option<SplitResult<'a, K, V, marker::Leaf>>, *mut V) {
866 if self.node.len() < CAPACITY {
867 let val_ptr = self.insert_fit(key, val);
870 let (middle_kv_idx, insertion) = splitpoint(self.idx);
871 let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
872 let mut result = middle.split();
873 let mut insertion_edge = match insertion {
874 LeftOrRight::Left(insert_idx) => unsafe {
875 Handle::new_edge(result.left.reborrow_mut(), insert_idx)
877 LeftOrRight::Right(insert_idx) => unsafe {
878 Handle::new_edge(result.right.borrow_mut(), insert_idx)
881 let val_ptr = insertion_edge.insert_fit(key, val);
882 (Some(result), val_ptr)
887 impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
888 /// Fixes the parent pointer and index in the child node that this edge
889 /// links to. This is useful when the ordering of edges has been changed,
890 fn correct_parent_link(self) {
891 // Create backpointer without invalidating other references to the node.
892 let ptr = unsafe { NonNull::new_unchecked(NodeRef::as_internal_ptr(&self.node)) };
894 let mut child = self.descend();
895 child.set_parent_link(ptr, idx);
899 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
900 /// Inserts a new key-value pair and an edge that will go to the right of that new pair
901 /// between this edge and the key-value pair to the right of this edge. This method assumes
902 /// that there is enough space in the node for the new pair to fit.
903 fn insert_fit(&mut self, key: K, val: V, edge: Root<K, V>) {
904 debug_assert!(self.node.len() < CAPACITY);
905 debug_assert!(edge.height == self.node.height - 1);
906 let new_len = self.node.len() + 1;
909 slice_insert(self.node.key_area_mut(..new_len), self.idx, key);
910 slice_insert(self.node.val_area_mut(..new_len), self.idx, val);
911 slice_insert(self.node.edge_area_mut(..new_len + 1), self.idx + 1, edge.node);
912 *self.node.len_mut() = new_len as u16;
914 self.node.correct_childrens_parent_links(self.idx + 1..new_len + 1);
918 /// Inserts a new key-value pair and an edge that will go to the right of that new pair
919 /// between this edge and the key-value pair to the right of this edge. This method splits
920 /// the node if there isn't enough room.
926 ) -> Option<SplitResult<'a, K, V, marker::Internal>> {
927 assert!(edge.height == self.node.height - 1);
929 if self.node.len() < CAPACITY {
930 self.insert_fit(key, val, edge);
933 let (middle_kv_idx, insertion) = splitpoint(self.idx);
934 let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
935 let mut result = middle.split();
936 let mut insertion_edge = match insertion {
937 LeftOrRight::Left(insert_idx) => unsafe {
938 Handle::new_edge(result.left.reborrow_mut(), insert_idx)
940 LeftOrRight::Right(insert_idx) => unsafe {
941 Handle::new_edge(result.right.borrow_mut(), insert_idx)
944 insertion_edge.insert_fit(key, val, edge);
950 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
951 /// Inserts a new key-value pair between the key-value pairs to the right and left of
952 /// this edge. This method splits the node if there isn't enough room, and tries to
953 /// insert the split off portion into the parent node recursively, until the root is reached.
955 /// If the returned result is some `SplitResult`, the `left` field will be the root node.
956 /// The returned pointer points to the inserted value, which in the case of `SplitResult`
957 /// is in the `left` or `right` tree.
958 pub fn insert_recursing(
962 ) -> (Option<SplitResult<'a, K, V, marker::LeafOrInternal>>, *mut V) {
963 let (mut split, val_ptr) = match self.insert(key, value) {
964 (None, val_ptr) => return (None, val_ptr),
965 (Some(split), val_ptr) => (split.forget_node_type(), val_ptr),
969 split = match split.left.ascend() {
970 Ok(parent) => match parent.insert(split.kv.0, split.kv.1, split.right) {
971 None => return (None, val_ptr),
972 Some(split) => split.forget_node_type(),
974 Err(root) => return (Some(SplitResult { left: root, ..split }), val_ptr),
980 impl<BorrowType: marker::BorrowType, K, V>
981 Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>
983 /// Finds the node pointed to by this edge.
985 /// The method name assumes you picture trees with the root node on top.
987 /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
988 /// both, upon success, do nothing.
989 pub fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
990 assert!(BorrowType::PERMITS_TRAVERSAL);
991 // We need to use raw pointers to nodes because, if BorrowType is
992 // marker::ValMut, there might be outstanding mutable references to
993 // values that we must not invalidate. There's no worry accessing the
994 // height field because that value is copied. Beware that, once the
995 // node pointer is dereferenced, we access the edges array with a
996 // reference (Rust issue #73987) and invalidate any other references
997 // to or inside the array, should any be around.
998 let parent_ptr = NodeRef::as_internal_ptr(&self.node);
999 let node = unsafe { (*parent_ptr).edges.get_unchecked(self.idx).assume_init_read() };
1000 NodeRef { node, height: self.node.height - 1, _marker: PhantomData }
1004 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Immut<'a>, K, V, NodeType>, marker::KV> {
1005 pub fn into_kv(self) -> (&'a K, &'a V) {
1006 debug_assert!(self.idx < self.node.len());
1007 let leaf = self.node.into_leaf();
1008 let k = unsafe { leaf.keys.get_unchecked(self.idx).assume_init_ref() };
1009 let v = unsafe { leaf.vals.get_unchecked(self.idx).assume_init_ref() };
1014 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
1015 pub fn key_mut(&mut self) -> &mut K {
1016 unsafe { self.node.key_area_mut(self.idx).assume_init_mut() }
1019 pub fn into_val_mut(self) -> &'a mut V {
1020 debug_assert!(self.idx < self.node.len());
1021 let leaf = self.node.into_leaf_mut();
1022 unsafe { leaf.vals.get_unchecked_mut(self.idx).assume_init_mut() }
1026 impl<'a, K, V, NodeType> Handle<NodeRef<marker::ValMut<'a>, K, V, NodeType>, marker::KV> {
1027 pub fn into_kv_valmut(self) -> (&'a K, &'a mut V) {
1028 unsafe { self.node.into_key_val_mut_at(self.idx) }
1032 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
1033 pub fn kv_mut(&mut self) -> (&mut K, &mut V) {
1034 debug_assert!(self.idx < self.node.len());
1035 // We cannot call separate key and value methods, because calling the second one
1036 // invalidates the reference returned by the first.
1038 let leaf = self.node.as_leaf_mut();
1039 let key = leaf.keys.get_unchecked_mut(self.idx).assume_init_mut();
1040 let val = leaf.vals.get_unchecked_mut(self.idx).assume_init_mut();
1045 /// Replaces the key and value that the KV handle refers to.
1046 pub fn replace_kv(&mut self, k: K, v: V) -> (K, V) {
1047 let (key, val) = self.kv_mut();
1048 (mem::replace(key, k), mem::replace(val, v))
1052 impl<K, V, NodeType> Handle<NodeRef<marker::Dying, K, V, NodeType>, marker::KV> {
1053 /// Extracts the key and value that the KV handle refers to.
1055 /// The node that the handle refers to must not yet have been deallocated.
1056 pub unsafe fn into_key_val(mut self) -> (K, V) {
1057 debug_assert!(self.idx < self.node.len());
1058 let leaf = self.node.as_leaf_dying();
1060 let key = leaf.keys.get_unchecked_mut(self.idx).assume_init_read();
1061 let val = leaf.vals.get_unchecked_mut(self.idx).assume_init_read();
1066 /// Drops the key and value that the KV handle refers to.
1068 /// The node that the handle refers to must not yet have been deallocated.
1070 pub unsafe fn drop_key_val(mut self) {
1071 debug_assert!(self.idx < self.node.len());
1072 let leaf = self.node.as_leaf_dying();
1074 leaf.keys.get_unchecked_mut(self.idx).assume_init_drop();
1075 leaf.vals.get_unchecked_mut(self.idx).assume_init_drop();
1080 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
1081 /// Helps implementations of `split` for a particular `NodeType`,
1082 /// by taking care of leaf data.
1083 fn split_leaf_data(&mut self, new_node: &mut LeafNode<K, V>) -> (K, V) {
1084 debug_assert!(self.idx < self.node.len());
1085 let old_len = self.node.len();
1086 let new_len = old_len - self.idx - 1;
1087 new_node.len = new_len as u16;
1089 let k = self.node.key_area_mut(self.idx).assume_init_read();
1090 let v = self.node.val_area_mut(self.idx).assume_init_read();
1093 self.node.key_area_mut(self.idx + 1..old_len),
1094 &mut new_node.keys[..new_len],
1097 self.node.val_area_mut(self.idx + 1..old_len),
1098 &mut new_node.vals[..new_len],
1101 *self.node.len_mut() = self.idx as u16;
1107 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
1108 /// Splits the underlying node into three parts:
1110 /// - The node is truncated to only contain the key-value pairs to the left of
1112 /// - The key and value pointed to by this handle are extracted.
1113 /// - All the key-value pairs to the right of this handle are put into a newly
1115 pub fn split(mut self) -> SplitResult<'a, K, V, marker::Leaf> {
1116 let mut new_node = LeafNode::new();
1118 let kv = self.split_leaf_data(&mut new_node);
1120 let right = NodeRef::from_new_leaf(new_node);
1121 SplitResult { left: self.node, kv, right }
1124 /// Removes the key-value pair pointed to by this handle and returns it, along with the edge
1125 /// that the key-value pair collapsed into.
1128 ) -> ((K, V), Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>) {
1129 let old_len = self.node.len();
1131 let k = slice_remove(self.node.key_area_mut(..old_len), self.idx);
1132 let v = slice_remove(self.node.val_area_mut(..old_len), self.idx);
1133 *self.node.len_mut() = (old_len - 1) as u16;
1134 ((k, v), self.left_edge())
1139 impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> {
1140 /// Splits the underlying node into three parts:
1142 /// - The node is truncated to only contain the edges and key-value pairs to the
1143 /// left of this handle.
1144 /// - The key and value pointed to by this handle are extracted.
1145 /// - All the edges and key-value pairs to the right of this handle are put into
1146 /// a newly allocated node.
1147 pub fn split(mut self) -> SplitResult<'a, K, V, marker::Internal> {
1148 let old_len = self.node.len();
1150 let mut new_node = InternalNode::new();
1151 let kv = self.split_leaf_data(&mut new_node.data);
1152 let new_len = usize::from(new_node.data.len);
1154 self.node.edge_area_mut(self.idx + 1..old_len + 1),
1155 &mut new_node.edges[..new_len + 1],
1158 let height = self.node.height;
1159 let right = NodeRef::from_new_internal(new_node, height);
1161 SplitResult { left: self.node, kv, right }
1166 /// Represents a session for evaluating and performing a balancing operation
1167 /// around an internal key-value pair.
1168 pub struct BalancingContext<'a, K, V> {
1169 parent: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV>,
1170 left_child: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1171 right_child: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1174 impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> {
1175 pub fn consider_for_balancing(self) -> BalancingContext<'a, K, V> {
1176 let self1 = unsafe { ptr::read(&self) };
1177 let self2 = unsafe { ptr::read(&self) };
1180 left_child: self1.left_edge().descend(),
1181 right_child: self2.right_edge().descend(),
1186 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1187 /// Chooses a balancing context involving the node as a child, thus between
1188 /// the KV immediately to the left or to the right in the parent node.
1189 /// Returns an `Err` if there is no parent.
1190 /// Panics if the parent is empty.
1192 /// Prefers the left side, to be optimal if the given node is somehow
1193 /// underfull, meaning here only that it has fewer elements than its left
1194 /// sibling and than its right sibling, if they exist. In that case,
1195 /// merging with the left sibling is faster, since we only need to move
1196 /// the node's N elements, instead of shifting them to the right and moving
1197 /// more than N elements in front. Stealing from the left sibling is also
1198 /// typically faster, since we only need to shift the node's N elements to
1199 /// the right, instead of shifting at least N of the sibling's elements to
1201 pub fn choose_parent_kv(self) -> Result<LeftOrRight<BalancingContext<'a, K, V>>, Self> {
1202 match unsafe { ptr::read(&self) }.ascend() {
1203 Ok(parent_edge) => match parent_edge.left_kv() {
1204 Ok(left_parent_kv) => Ok(LeftOrRight::Left(BalancingContext {
1205 parent: unsafe { ptr::read(&left_parent_kv) },
1206 left_child: left_parent_kv.left_edge().descend(),
1209 Err(parent_edge) => match parent_edge.right_kv() {
1210 Ok(right_parent_kv) => Ok(LeftOrRight::Right(BalancingContext {
1211 parent: unsafe { ptr::read(&right_parent_kv) },
1213 right_child: right_parent_kv.right_edge().descend(),
1215 Err(_) => unreachable!("empty internal node"),
1218 Err(root) => Err(root),
1223 impl<'a, K, V> BalancingContext<'a, K, V> {
1224 pub fn left_child_len(&self) -> usize {
1225 self.left_child.len()
1228 pub fn right_child_len(&self) -> usize {
1229 self.right_child.len()
1232 pub fn into_left_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1236 pub fn into_right_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1240 /// Returns whether merging is possible, i.e., whether there is enough room
1241 /// in a node to combine the central KV with both adjacent child nodes.
1242 pub fn can_merge(&self) -> bool {
1243 self.left_child.len() + 1 + self.right_child.len() <= CAPACITY
1247 impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
1248 /// Performs a merge and lets a closure decide what to return.
1251 NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
1252 NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1259 let Handle { node: mut parent_node, idx: parent_idx, _marker } = self.parent;
1260 let old_parent_len = parent_node.len();
1261 let mut left_node = self.left_child;
1262 let old_left_len = left_node.len();
1263 let mut right_node = self.right_child;
1264 let right_len = right_node.len();
1265 let new_left_len = old_left_len + 1 + right_len;
1267 assert!(new_left_len <= CAPACITY);
1270 *left_node.len_mut() = new_left_len as u16;
1272 let parent_key = slice_remove(parent_node.key_area_mut(..old_parent_len), parent_idx);
1273 left_node.key_area_mut(old_left_len).write(parent_key);
1275 right_node.key_area_mut(..right_len),
1276 left_node.key_area_mut(old_left_len + 1..new_left_len),
1279 let parent_val = slice_remove(parent_node.val_area_mut(..old_parent_len), parent_idx);
1280 left_node.val_area_mut(old_left_len).write(parent_val);
1282 right_node.val_area_mut(..right_len),
1283 left_node.val_area_mut(old_left_len + 1..new_left_len),
1286 slice_remove(&mut parent_node.edge_area_mut(..old_parent_len + 1), parent_idx + 1);
1287 parent_node.correct_childrens_parent_links(parent_idx + 1..old_parent_len);
1288 *parent_node.len_mut() -= 1;
1290 if parent_node.height > 1 {
1291 // SAFETY: the height of the nodes being merged is one below the height
1292 // of the node of this edge, thus above zero, so they are internal.
1293 let mut left_node = left_node.reborrow_mut().cast_to_internal_unchecked();
1294 let mut right_node = right_node.cast_to_internal_unchecked();
1296 right_node.edge_area_mut(..right_len + 1),
1297 left_node.edge_area_mut(old_left_len + 1..new_left_len + 1),
1300 left_node.correct_childrens_parent_links(old_left_len + 1..new_left_len + 1);
1302 Global.deallocate(right_node.node.cast(), Layout::new::<InternalNode<K, V>>());
1304 Global.deallocate(right_node.node.cast(), Layout::new::<LeafNode<K, V>>());
1307 result(parent_node, left_node)
1310 /// Merges the parent's key-value pair and both adjacent child nodes into
1311 /// the left child node and returns the shrunk parent node.
1313 /// Panics unless we `.can_merge()`.
1314 pub fn merge_tracking_parent(self) -> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
1315 self.do_merge(|parent, _child| parent)
1318 /// Merges the parent's key-value pair and both adjacent child nodes into
1319 /// the left child node and returns that child node.
1321 /// Panics unless we `.can_merge()`.
1322 pub fn merge_tracking_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1323 self.do_merge(|_parent, child| child)
1326 /// Merges the parent's key-value pair and both adjacent child nodes into
1327 /// the left child node and returns the edge handle in that child node
1328 /// where the tracked child edge ended up,
1330 /// Panics unless we `.can_merge()`.
1331 pub fn merge_tracking_child_edge(
1333 track_edge_idx: LeftOrRight<usize>,
1334 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1335 let old_left_len = self.left_child.len();
1336 let right_len = self.right_child.len();
1337 assert!(match track_edge_idx {
1338 LeftOrRight::Left(idx) => idx <= old_left_len,
1339 LeftOrRight::Right(idx) => idx <= right_len,
1341 let child = self.merge_tracking_child();
1342 let new_idx = match track_edge_idx {
1343 LeftOrRight::Left(idx) => idx,
1344 LeftOrRight::Right(idx) => old_left_len + 1 + idx,
1346 unsafe { Handle::new_edge(child, new_idx) }
1349 /// Removes a key-value pair from the left child and places it in the key-value storage
1350 /// of the parent, while pushing the old parent key-value pair into the right child.
1351 /// Returns a handle to the edge in the right child corresponding to where the original
1352 /// edge specified by `track_right_edge_idx` ended up.
1355 track_right_edge_idx: usize,
1356 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1357 self.bulk_steal_left(1);
1358 unsafe { Handle::new_edge(self.right_child, 1 + track_right_edge_idx) }
1361 /// Removes a key-value pair from the right child and places it in the key-value storage
1362 /// of the parent, while pushing the old parent key-value pair onto the left child.
1363 /// Returns a handle to the edge in the left child specified by `track_left_edge_idx`,
1364 /// which didn't move.
1367 track_left_edge_idx: usize,
1368 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1369 self.bulk_steal_right(1);
1370 unsafe { Handle::new_edge(self.left_child, track_left_edge_idx) }
1373 /// This does stealing similar to `steal_left` but steals multiple elements at once.
1374 pub fn bulk_steal_left(&mut self, count: usize) {
1377 let left_node = &mut self.left_child;
1378 let old_left_len = left_node.len();
1379 let right_node = &mut self.right_child;
1380 let old_right_len = right_node.len();
1382 // Make sure that we may steal safely.
1383 assert!(old_right_len + count <= CAPACITY);
1384 assert!(old_left_len >= count);
1386 let new_left_len = old_left_len - count;
1387 let new_right_len = old_right_len + count;
1388 *left_node.len_mut() = new_left_len as u16;
1389 *right_node.len_mut() = new_right_len as u16;
1393 // Make room for stolen elements in the right child.
1394 slice_shr(right_node.key_area_mut(..new_right_len), count);
1395 slice_shr(right_node.val_area_mut(..new_right_len), count);
1397 // Move elements from the left child to the right one.
1399 left_node.key_area_mut(new_left_len + 1..old_left_len),
1400 right_node.key_area_mut(..count - 1),
1403 left_node.val_area_mut(new_left_len + 1..old_left_len),
1404 right_node.val_area_mut(..count - 1),
1407 // Move the left-most stolen pair to the parent.
1408 let k = left_node.key_area_mut(new_left_len).assume_init_read();
1409 let v = left_node.val_area_mut(new_left_len).assume_init_read();
1410 let (k, v) = self.parent.replace_kv(k, v);
1412 // Move parent's key-value pair to the right child.
1413 right_node.key_area_mut(count - 1).write(k);
1414 right_node.val_area_mut(count - 1).write(v);
1417 match (left_node.reborrow_mut().force(), right_node.reborrow_mut().force()) {
1418 (ForceResult::Internal(mut left), ForceResult::Internal(mut right)) => {
1419 // Make room for stolen edges.
1420 slice_shr(right.edge_area_mut(..new_right_len + 1), count);
1424 left.edge_area_mut(new_left_len + 1..old_left_len + 1),
1425 right.edge_area_mut(..count),
1428 right.correct_childrens_parent_links(0..new_right_len + 1);
1430 (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
1431 _ => unreachable!(),
1436 /// The symmetric clone of `bulk_steal_left`.
1437 pub fn bulk_steal_right(&mut self, count: usize) {
1440 let left_node = &mut self.left_child;
1441 let old_left_len = left_node.len();
1442 let right_node = &mut self.right_child;
1443 let old_right_len = right_node.len();
1445 // Make sure that we may steal safely.
1446 assert!(old_left_len + count <= CAPACITY);
1447 assert!(old_right_len >= count);
1449 let new_left_len = old_left_len + count;
1450 let new_right_len = old_right_len - count;
1451 *left_node.len_mut() = new_left_len as u16;
1452 *right_node.len_mut() = new_right_len as u16;
1456 // Move the right-most stolen pair to the parent.
1457 let k = right_node.key_area_mut(count - 1).assume_init_read();
1458 let v = right_node.val_area_mut(count - 1).assume_init_read();
1459 let (k, v) = self.parent.replace_kv(k, v);
1461 // Move parent's key-value pair to the left child.
1462 left_node.key_area_mut(old_left_len).write(k);
1463 left_node.val_area_mut(old_left_len).write(v);
1465 // Move elements from the right child to the left one.
1467 right_node.key_area_mut(..count - 1),
1468 left_node.key_area_mut(old_left_len + 1..new_left_len),
1471 right_node.val_area_mut(..count - 1),
1472 left_node.val_area_mut(old_left_len + 1..new_left_len),
1475 // Fill gap where stolen elements used to be.
1476 slice_shl(right_node.key_area_mut(..old_right_len), count);
1477 slice_shl(right_node.val_area_mut(..old_right_len), count);
1480 match (left_node.reborrow_mut().force(), right_node.reborrow_mut().force()) {
1481 (ForceResult::Internal(mut left), ForceResult::Internal(mut right)) => {
1484 right.edge_area_mut(..count),
1485 left.edge_area_mut(old_left_len + 1..new_left_len + 1),
1488 // Fill gap where stolen edges used to be.
1489 slice_shl(right.edge_area_mut(..old_right_len + 1), count);
1491 left.correct_childrens_parent_links(old_left_len + 1..new_left_len + 1);
1492 right.correct_childrens_parent_links(0..new_right_len + 1);
1494 (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
1495 _ => unreachable!(),
1501 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
1502 pub fn forget_node_type(
1504 ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
1505 unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
1509 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge> {
1510 pub fn forget_node_type(
1512 ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
1513 unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
1517 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::KV> {
1518 pub fn forget_node_type(
1520 ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV> {
1521 unsafe { Handle::new_kv(self.node.forget_type(), self.idx) }
1525 impl<BorrowType, K, V, Type> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, Type> {
1526 /// Checks whether the underlying node is an `Internal` node or a `Leaf` node.
1530 Handle<NodeRef<BorrowType, K, V, marker::Leaf>, Type>,
1531 Handle<NodeRef<BorrowType, K, V, marker::Internal>, Type>,
1533 match self.node.force() {
1534 ForceResult::Leaf(node) => {
1535 ForceResult::Leaf(Handle { node, idx: self.idx, _marker: PhantomData })
1537 ForceResult::Internal(node) => {
1538 ForceResult::Internal(Handle { node, idx: self.idx, _marker: PhantomData })
1544 impl<'a, K, V, Type> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, Type> {
1545 /// Unsafely asserts to the compiler the static information that the handle's node is a `Leaf`.
1546 pub unsafe fn cast_to_leaf_unchecked(
1548 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, Type> {
1549 let node = unsafe { self.node.cast_to_leaf_unchecked() };
1550 Handle { node, idx: self.idx, _marker: PhantomData }
1554 impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1555 /// Move the suffix after `self` from one node to another one. `right` must be empty.
1556 /// The first edge of `right` remains unchanged.
1559 right: &mut NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1562 let new_left_len = self.idx;
1563 let mut left_node = self.reborrow_mut().into_node();
1564 let old_left_len = left_node.len();
1566 let new_right_len = old_left_len - new_left_len;
1567 let mut right_node = right.reborrow_mut();
1569 assert!(right_node.len() == 0);
1570 assert!(left_node.height == right_node.height);
1572 if new_right_len > 0 {
1573 *left_node.len_mut() = new_left_len as u16;
1574 *right_node.len_mut() = new_right_len as u16;
1577 left_node.key_area_mut(new_left_len..old_left_len),
1578 right_node.key_area_mut(..new_right_len),
1581 left_node.val_area_mut(new_left_len..old_left_len),
1582 right_node.val_area_mut(..new_right_len),
1584 match (left_node.force(), right_node.force()) {
1585 (ForceResult::Internal(mut left), ForceResult::Internal(mut right)) => {
1587 left.edge_area_mut(new_left_len + 1..old_left_len + 1),
1588 right.edge_area_mut(1..new_right_len + 1),
1590 right.correct_childrens_parent_links(1..new_right_len + 1);
1592 (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
1593 _ => unreachable!(),
1600 pub enum ForceResult<Leaf, Internal> {
1605 /// Result of insertion, when a node needed to expand beyond its capacity.
1606 pub struct SplitResult<'a, K, V, NodeType> {
1607 // Altered node in existing tree with elements and edges that belong to the left of `kv`.
1608 pub left: NodeRef<marker::Mut<'a>, K, V, NodeType>,
1609 // Some key and value that existed before and were split off, to be inserted elsewhere.
1611 // Owned, unattached, new node with elements and edges that belong to the right of `kv`.
1612 pub right: NodeRef<marker::Owned, K, V, NodeType>,
1615 impl<'a, K, V> SplitResult<'a, K, V, marker::Leaf> {
1616 pub fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
1617 SplitResult { left: self.left.forget_type(), kv: self.kv, right: self.right.forget_type() }
1621 impl<'a, K, V> SplitResult<'a, K, V, marker::Internal> {
1622 pub fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
1623 SplitResult { left: self.left.forget_type(), kv: self.kv, right: self.right.forget_type() }
1628 use core::marker::PhantomData;
1631 pub enum Internal {}
1632 pub enum LeafOrInternal {}
1636 pub struct Immut<'a>(PhantomData<&'a ()>);
1637 pub struct Mut<'a>(PhantomData<&'a mut ()>);
1638 pub struct ValMut<'a>(PhantomData<&'a mut ()>);
1640 pub trait BorrowType {
1641 // Whether node references of this borrow type allow traversing
1642 // to other nodes in the tree.
1643 const PERMITS_TRAVERSAL: bool = true;
1645 impl BorrowType for Owned {
1646 // Traversal isn't needed, it happens using the result of `borrow_mut`.
1647 // By disabling traversal, and only creating new references to roots,
1648 // we know that every reference of the `Owned` type is to a root node.
1649 const PERMITS_TRAVERSAL: bool = false;
1651 impl BorrowType for Dying {}
1652 impl<'a> BorrowType for Immut<'a> {}
1653 impl<'a> BorrowType for Mut<'a> {}
1654 impl<'a> BorrowType for ValMut<'a> {}
1660 /// Inserts a value into a slice of initialized elements followed by one uninitialized element.
1663 /// The slice has more than `idx` elements.
1664 unsafe fn slice_insert<T>(slice: &mut [MaybeUninit<T>], idx: usize, val: T) {
1666 let len = slice.len();
1667 debug_assert!(len > idx);
1668 let slice_ptr = slice.as_mut_ptr();
1670 ptr::copy(slice_ptr.add(idx), slice_ptr.add(idx + 1), len - idx - 1);
1672 (*slice_ptr.add(idx)).write(val);
1676 /// Removes and returns a value from a slice of all initialized elements, leaving behind one
1677 /// trailing uninitialized element.
1680 /// The slice has more than `idx` elements.
1681 unsafe fn slice_remove<T>(slice: &mut [MaybeUninit<T>], idx: usize) -> T {
1683 let len = slice.len();
1684 debug_assert!(idx < len);
1685 let slice_ptr = slice.as_mut_ptr();
1686 let ret = (*slice_ptr.add(idx)).assume_init_read();
1687 ptr::copy(slice_ptr.add(idx + 1), slice_ptr.add(idx), len - idx - 1);
1692 /// Shifts the elements in a slice `distance` positions to the left.
1695 /// The slice has at least `distance` elements.
1696 unsafe fn slice_shl<T>(slice: &mut [MaybeUninit<T>], distance: usize) {
1698 let slice_ptr = slice.as_mut_ptr();
1699 ptr::copy(slice_ptr.add(distance), slice_ptr, slice.len() - distance);
1703 /// Shifts the elements in a slice `distance` positions to the right.
1706 /// The slice has at least `distance` elements.
1707 unsafe fn slice_shr<T>(slice: &mut [MaybeUninit<T>], distance: usize) {
1709 let slice_ptr = slice.as_mut_ptr();
1710 ptr::copy(slice_ptr, slice_ptr.add(distance), slice.len() - distance);
1714 /// Moves all values from a slice of initialized elements to a slice
1715 /// of uninitialized elements, leaving behind `src` as all uninitialized.
1716 /// Works like `dst.copy_from_slice(src)` but does not require `T` to be `Copy`.
1717 fn move_to_slice<T>(src: &mut [MaybeUninit<T>], dst: &mut [MaybeUninit<T>]) {
1718 assert!(src.len() == dst.len());
1720 ptr::copy_nonoverlapping(src.as_ptr(), dst.as_mut_ptr(), src.len());