1// This is an attempt at an implementation following the ideal
2//
3// ```
4// struct BTreeMap<K, V> {
5// height: usize,
6// root: Option<Box<Node<K, V, height>>>
7// }
8//
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)>,
14// len: u16,
15// }
16// ```
17//
18// Since Rust doesn't actually have dependent types and polymorphic recursion,
19// we make do with lots of unsafety.
20
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:
25//
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.
33
34use core::marker::PhantomData;
35use core::mem::{self, MaybeUninit};
36use core::ptr::{self, NonNull};
37use core::slice::SliceIndex;
38
39use crate::alloc::{Allocator, Layout};
40use crate::boxed::Box;
41
42const B: usize = 6;
43pub(super) const CAPACITY: usize = 2 * B - 1;
44pub(super) const MIN_LEN_AFTER_SPLIT: usize = B - 1;
45const KV_IDX_CENTER: usize = B - 1;
46const EDGE_IDX_LEFT_OF_CENTER: usize = B - 1;
47const EDGE_IDX_RIGHT_OF_CENTER: usize = B;
48
49/// The underlying representation of leaf nodes and part of the representation of internal nodes.
50struct LeafNode<K, V> {
51 /// We want to be covariant in `K` and `V`.
52 parent: Option<NonNull<InternalNode<K, V>>>,
53
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>,
58
59 /// The number of keys and values this node stores.
60 len: u16,
61
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],
66}
67
68impl<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.
73 unsafe {
74 // parent_idx, keys, and vals are all MaybeUninit
75 (&raw mut (*this).parent).write(val:None);
76 (&raw mut (*this).len).write(val:0);
77 }
78 }
79
80 /// Creates a new boxed `LeafNode`.
81 fn new<A: Allocator + Clone>(alloc: A) -> Box<Self, A> {
82 unsafe {
83 let mut leaf: Box>, …> = Box::new_uninit_in(alloc);
84 LeafNode::init(this:leaf.as_mut_ptr());
85 leaf.assume_init()
86 }
87 }
88}
89
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)`.
95#[repr(C)]
96// gdb_providers.py uses this type name for introspection.
97struct InternalNode<K, V> {
98 data: LeafNode<K, V>,
99
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],
104}
105
106impl<K, V> InternalNode<K, V> {
107 /// Creates a new boxed `InternalNode`.
108 ///
109 /// # Safety
110 /// An invariant of internal nodes is that they have at least one
111 /// initialized and valid edge. This function does not set up
112 /// such an edge.
113 unsafe fn new<A: Allocator + Clone>(alloc: A) -> Box<Self, A> {
114 unsafe {
115 let mut node: Box>, …> = Box::<Self, _>::new_uninit_in(alloc);
116 // We only need to initialize the data; the edges are MaybeUninit.
117 LeafNode::init(&raw mut (*node.as_mut_ptr()).data);
118 node.assume_init()
119 }
120 }
121}
122
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>`.
125///
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.
129type BoxedNode<K, V> = NonNull<LeafNode<K, V>>;
130
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
135// correct variance.
136///
137/// A reference to a node.
138///
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`.
160///
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`.
172///
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.
182pub(super) 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`.
188 height: usize,
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)>,
193}
194
195/// The root node of an owned tree.
196///
197/// Note that this does not have a destructor, and must be cleaned up manually.
198pub(super) type Root<K, V> = NodeRef<marker::Owned, K, V, marker::LeafOrInternal>;
199
200impl<'a, K: 'a, V: 'a, Type> Copy for NodeRef<marker::Immut<'a>, K, V, Type> {}
201impl<'a, K: 'a, V: 'a, Type> Clone for NodeRef<marker::Immut<'a>, K, V, Type> {
202 fn clone(&self) -> Self {
203 *self
204 }
205}
206
207unsafe impl<BorrowType, K: Sync, V: Sync, Type> Sync for NodeRef<BorrowType, K, V, Type> {}
208
209unsafe impl<K: Sync, V: Sync, Type> Send for NodeRef<marker::Immut<'_>, K, V, Type> {}
210unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Mut<'_>, K, V, Type> {}
211unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::ValMut<'_>, K, V, Type> {}
212unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Owned, K, V, Type> {}
213unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Dying, K, V, Type> {}
214
215impl<K, V> NodeRef<marker::Owned, K, V, marker::Leaf> {
216 pub(super) fn new_leaf<A: Allocator + Clone>(alloc: A) -> Self {
217 Self::from_new_leaf(LeafNode::new(alloc))
218 }
219
220 fn from_new_leaf<A: Allocator + Clone>(leaf: Box<LeafNode<K, V>, A>) -> Self {
221 NodeRef { height: 0, node: NonNull::from(Box::leak(leaf)), _marker: PhantomData }
222 }
223}
224
225impl<K, V> NodeRef<marker::Owned, K, V, marker::Internal> {
226 fn new_internal<A: Allocator + Clone>(child: Root<K, V>, alloc: A) -> Self {
227 let mut new_node: Box, A> = unsafe { InternalNode::new(alloc) };
228 new_node.edges[0].write(val:child.node);
229 unsafe { NodeRef::from_new_internal(internal:new_node, height:child.height + 1) }
230 }
231
232 /// # Safety
233 /// `height` must not be zero.
234 unsafe fn from_new_internal<A: Allocator + Clone>(
235 internal: Box<InternalNode<K, V>, A>,
236 height: usize,
237 ) -> Self {
238 debug_assert!(height > 0);
239 let node: NonNull> = NonNull::from(Box::leak(internal)).cast();
240 let mut this: NodeRef = NodeRef { height, node, _marker: PhantomData };
241 this.borrow_mut().correct_all_childrens_parent_links();
242 this
243 }
244}
245
246impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
247 /// Unpack a node reference that was packed as `NodeRef::parent`.
248 fn from_internal(node: NonNull<InternalNode<K, V>>, height: usize) -> Self {
249 debug_assert!(height > 0);
250 NodeRef { height, node: node.cast(), _marker: PhantomData }
251 }
252}
253
254impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
255 /// Exposes the data of an internal node.
256 ///
257 /// Returns a raw ptr to avoid invalidating other references to this node.
258 fn as_internal_ptr(this: &Self) -> *mut InternalNode<K, V> {
259 // SAFETY: the static node type is `Internal`.
260 this.node.as_ptr() as *mut InternalNode<K, V>
261 }
262}
263
264impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
265 /// Borrows exclusive access to the data of an internal node.
266 fn as_internal_mut(&mut self) -> &mut InternalNode<K, V> {
267 let ptr: *mut InternalNode = Self::as_internal_ptr(self);
268 unsafe { &mut *ptr }
269 }
270}
271
272impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
273 /// Finds the length of the node. This is the number of keys or values.
274 /// The number of edges is `len() + 1`.
275 /// Note that, despite being safe, calling this function can have the side effect
276 /// of invalidating mutable references that unsafe code has created.
277 pub(super) fn len(&self) -> usize {
278 // Crucially, we only access the `len` field here. If BorrowType is marker::ValMut,
279 // there might be outstanding mutable references to values that we must not invalidate.
280 unsafe { usize::from((*Self::as_leaf_ptr(self)).len) }
281 }
282
283 /// Returns the number of levels that the node and leaves are apart. Zero
284 /// height means the node is a leaf itself. If you picture trees with the
285 /// root on top, the number says at which elevation the node appears.
286 /// If you picture trees with leaves on top, the number says how high
287 /// the tree extends above the node.
288 pub(super) fn height(&self) -> usize {
289 self.height
290 }
291
292 /// Temporarily takes out another, immutable reference to the same node.
293 pub(super) fn reborrow(&self) -> NodeRef<marker::Immut<'_>, K, V, Type> {
294 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
295 }
296
297 /// Exposes the leaf portion of any leaf or internal node.
298 ///
299 /// Returns a raw ptr to avoid invalidating other references to this node.
300 fn as_leaf_ptr(this: &Self) -> *mut LeafNode<K, V> {
301 // The node must be valid for at least the LeafNode portion.
302 // This is not a reference in the NodeRef type because we don't know if
303 // it should be unique or shared.
304 this.node.as_ptr()
305 }
306}
307
308impl<BorrowType: marker::BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
309 /// Finds the parent of the current node. Returns `Ok(handle)` if the current
310 /// node actually has a parent, where `handle` points to the edge of the parent
311 /// that points to the current node. Returns `Err(self)` if the current node has
312 /// no parent, giving back the original `NodeRef`.
313 ///
314 /// The method name assumes you picture trees with the root node on top.
315 ///
316 /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
317 /// both, upon success, do nothing.
318 pub(super) fn ascend(
319 self,
320 ) -> Result<Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>, Self> {
321 const {
322 assert!(BorrowType::TRAVERSAL_PERMIT);
323 }
324
325 // We need to use raw pointers to nodes because, if BorrowType is marker::ValMut,
326 // there might be outstanding mutable references to values that we must not invalidate.
327 let leaf_ptr: *const _ = Self::as_leaf_ptr(&self);
328 unsafe { (*leaf_ptr).parent }
329 .as_ref()
330 .map(|parent| Handle {
331 node: NodeRef::from_internal(*parent, self.height + 1),
332 idx: unsafe { usize::from((*leaf_ptr).parent_idx.assume_init()) },
333 _marker: PhantomData,
334 })
335 .ok_or(self)
336 }
337
338 pub(super) fn first_edge(self) -> Handle<Self, marker::Edge> {
339 unsafe { Handle::new_edge(self, 0) }
340 }
341
342 pub(super) fn last_edge(self) -> Handle<Self, marker::Edge> {
343 let len = self.len();
344 unsafe { Handle::new_edge(self, len) }
345 }
346
347 /// Note that `self` must be nonempty.
348 pub(super) fn first_kv(self) -> Handle<Self, marker::KV> {
349 let len = self.len();
350 assert!(len > 0);
351 unsafe { Handle::new_kv(self, 0) }
352 }
353
354 /// Note that `self` must be nonempty.
355 pub(super) fn last_kv(self) -> Handle<Self, marker::KV> {
356 let len = self.len();
357 assert!(len > 0);
358 unsafe { Handle::new_kv(self, len - 1) }
359 }
360}
361
362impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
363 /// Could be a public implementation of PartialEq, but only used in this module.
364 fn eq(&self, other: &Self) -> bool {
365 let Self { node: &NonNull>, height: &usize, _marker: &PhantomData<(BorrowType, …)> } = self;
366 if node.eq(&other.node) {
367 debug_assert_eq!(*height, other.height);
368 true
369 } else {
370 false
371 }
372 }
373}
374
375impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
376 /// Exposes the leaf portion of any leaf or internal node in an immutable tree.
377 fn into_leaf(self) -> &'a LeafNode<K, V> {
378 let ptr: *mut LeafNode = Self::as_leaf_ptr(&self);
379 // SAFETY: there can be no mutable references into this tree borrowed as `Immut`.
380 unsafe { &*ptr }
381 }
382
383 /// Borrows a view into the keys stored in the node.
384 pub(super) fn keys(&self) -> &[K] {
385 let leaf: &LeafNode = self.into_leaf();
386 unsafe { leaf.keys.get_unchecked(..usize::from(leaf.len)).assume_init_ref() }
387 }
388}
389
390impl<K, V> NodeRef<marker::Dying, K, V, marker::LeafOrInternal> {
391 /// Similar to `ascend`, gets a reference to a node's parent node, but also
392 /// deallocates the current node in the process. This is unsafe because the
393 /// current node will still be accessible despite being deallocated.
394 pub(super) unsafe fn deallocate_and_ascend<A: Allocator + Clone>(
395 self,
396 alloc: A,
397 ) -> Option<Handle<NodeRef<marker::Dying, K, V, marker::Internal>, marker::Edge>> {
398 let height: usize = self.height;
399 let node: NonNull> = self.node;
400 let ret: Option, …>> = self.ascend().ok();
401 unsafe {
402 alloc.deallocate(
403 ptr:node.cast(),
404 layout:if height > 0 {
405 Layout::new::<InternalNode<K, V>>()
406 } else {
407 Layout::new::<LeafNode<K, V>>()
408 },
409 );
410 }
411 ret
412 }
413}
414
415impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
416 /// Temporarily takes out another mutable reference to the same node. Beware, as
417 /// this method is very dangerous, doubly so since it might not immediately appear
418 /// dangerous.
419 ///
420 /// Because mutable pointers can roam anywhere around the tree, the returned
421 /// pointer can easily be used to make the original pointer dangling, out of
422 /// bounds, or invalid under stacked borrow rules.
423 // FIXME(@gereeter) consider adding yet another type parameter to `NodeRef`
424 // that restricts the use of navigation methods on reborrowed pointers,
425 // preventing this unsafety.
426 unsafe fn reborrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
427 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
428 }
429
430 /// Borrows exclusive access to the leaf portion of a leaf or internal node.
431 fn as_leaf_mut(&mut self) -> &mut LeafNode<K, V> {
432 let ptr = Self::as_leaf_ptr(self);
433 // SAFETY: we have exclusive access to the entire node.
434 unsafe { &mut *ptr }
435 }
436
437 /// Offers exclusive access to the leaf portion of a leaf or internal node.
438 fn into_leaf_mut(mut self) -> &'a mut LeafNode<K, V> {
439 let ptr = Self::as_leaf_ptr(&mut self);
440 // SAFETY: we have exclusive access to the entire node.
441 unsafe { &mut *ptr }
442 }
443
444 /// Returns a dormant copy of this node with its lifetime erased which can
445 /// be reawakened later.
446 pub(super) fn dormant(&self) -> NodeRef<marker::DormantMut, K, V, Type> {
447 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
448 }
449}
450
451impl<K, V, Type> NodeRef<marker::DormantMut, K, V, Type> {
452 /// Revert to the unique borrow initially captured.
453 ///
454 /// # Safety
455 ///
456 /// The reborrow must have ended, i.e., the reference returned by `new` and
457 /// all pointers and references derived from it, must not be used anymore.
458 pub(super) unsafe fn awaken<'a>(self) -> NodeRef<marker::Mut<'a>, K, V, Type> {
459 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
460 }
461}
462
463impl<K, V, Type> NodeRef<marker::Dying, K, V, Type> {
464 /// Borrows exclusive access to the leaf portion of a dying leaf or internal node.
465 fn as_leaf_dying(&mut self) -> &mut LeafNode<K, V> {
466 let ptr: *mut LeafNode = Self::as_leaf_ptr(self);
467 // SAFETY: we have exclusive access to the entire node.
468 unsafe { &mut *ptr }
469 }
470}
471
472impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
473 /// Borrows exclusive access to an element of the key storage area.
474 ///
475 /// # Safety
476 /// `index` is in bounds of 0..CAPACITY
477 unsafe fn key_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
478 where
479 I: SliceIndex<[MaybeUninit<K>], Output = Output>,
480 {
481 // SAFETY: the caller will not be able to call further methods on self
482 // until the key slice reference is dropped, as we have unique access
483 // for the lifetime of the borrow.
484 unsafe { self.as_leaf_mut().keys.as_mut_slice().get_unchecked_mut(index) }
485 }
486
487 /// Borrows exclusive access to an element or slice of the node's value storage area.
488 ///
489 /// # Safety
490 /// `index` is in bounds of 0..CAPACITY
491 unsafe fn val_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
492 where
493 I: SliceIndex<[MaybeUninit<V>], Output = Output>,
494 {
495 // SAFETY: the caller will not be able to call further methods on self
496 // until the value slice reference is dropped, as we have unique access
497 // for the lifetime of the borrow.
498 unsafe { self.as_leaf_mut().vals.as_mut_slice().get_unchecked_mut(index) }
499 }
500}
501
502impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
503 /// Borrows exclusive access to an element or slice of the node's storage area for edge contents.
504 ///
505 /// # Safety
506 /// `index` is in bounds of 0..CAPACITY + 1
507 unsafe fn edge_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
508 where
509 I: SliceIndex<[MaybeUninit<BoxedNode<K, V>>], Output = Output>,
510 {
511 // SAFETY: the caller will not be able to call further methods on self
512 // until the edge slice reference is dropped, as we have unique access
513 // for the lifetime of the borrow.
514 unsafe { self.as_internal_mut().edges.as_mut_slice().get_unchecked_mut(index) }
515 }
516}
517
518impl<'a, K, V, Type> NodeRef<marker::ValMut<'a>, K, V, Type> {
519 /// # Safety
520 /// - The node has more than `idx` initialized elements.
521 unsafe fn into_key_val_mut_at(mut self, idx: usize) -> (&'a K, &'a mut V) {
522 // We only create a reference to the one element we are interested in,
523 // to avoid aliasing with outstanding references to other elements,
524 // in particular, those returned to the caller in earlier iterations.
525 let leaf: *mut LeafNode = Self::as_leaf_ptr(&mut self);
526 let keys: *const [MaybeUninit; 11] = unsafe { &raw const (*leaf).keys };
527 let vals: *mut [MaybeUninit; 11] = unsafe { &raw mut (*leaf).vals };
528 // We must coerce to unsized array pointers because of Rust issue #74679.
529 let keys: *const [_] = keys;
530 let vals: *mut [_] = vals;
531 let key: &K = unsafe { (&*keys.get_unchecked(index:idx)).assume_init_ref() };
532 let val: &mut V = unsafe { (&mut *vals.get_unchecked_mut(index:idx)).assume_init_mut() };
533 (key, val)
534 }
535}
536
537impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
538 /// Borrows exclusive access to the length of the node.
539 pub(super) fn len_mut(&mut self) -> &mut u16 {
540 &mut self.as_leaf_mut().len
541 }
542}
543
544impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
545 /// # Safety
546 /// Every item returned by `range` is a valid edge index for the node.
547 unsafe fn correct_childrens_parent_links<R: Iterator<Item = usize>>(&mut self, range: R) {
548 for i: usize in range {
549 debug_assert!(i <= self.len());
550 unsafe { Handle::new_edge(self.reborrow_mut(), idx:i) }.correct_parent_link();
551 }
552 }
553
554 fn correct_all_childrens_parent_links(&mut self) {
555 let len: usize = self.len();
556 unsafe { self.correct_childrens_parent_links(range:0..=len) };
557 }
558}
559
560impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
561 /// Sets the node's link to its parent edge,
562 /// without invalidating other references to the node.
563 fn set_parent_link(&mut self, parent: NonNull<InternalNode<K, V>>, parent_idx: usize) {
564 let leaf: *mut LeafNode = Self::as_leaf_ptr(self);
565 unsafe { (*leaf).parent = Some(parent) };
566 unsafe { (*leaf).parent_idx.write(val:parent_idx as u16) };
567 }
568}
569
570impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
571 /// Clears the root's link to its parent edge.
572 fn clear_parent_link(&mut self) {
573 let mut root_node: NodeRef, K, V, LeafOrInternal> = self.borrow_mut();
574 let leaf: &mut LeafNode = root_node.as_leaf_mut();
575 leaf.parent = None;
576 }
577}
578
579impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
580 /// Returns a new owned tree, with its own root node that is initially empty.
581 pub(super) fn new<A: Allocator + Clone>(alloc: A) -> Self {
582 NodeRef::new_leaf(alloc).forget_type()
583 }
584
585 /// Adds a new internal node with a single edge pointing to the previous root node,
586 /// make that new node the root node, and return it. This increases the height by 1
587 /// and is the opposite of `pop_internal_level`.
588 pub(super) fn push_internal_level<A: Allocator + Clone>(
589 &mut self,
590 alloc: A,
591 ) -> NodeRef<marker::Mut<'_>, K, V, marker::Internal> {
592 super::mem::take_mut(self, |old_root| NodeRef::new_internal(old_root, alloc).forget_type());
593
594 // `self.borrow_mut()`, except that we just forgot we're internal now:
595 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
596 }
597
598 /// Removes the internal root node, using its first child as the new root node.
599 /// As it is intended only to be called when the root node has only one child,
600 /// no cleanup is done on any of the keys, values and other children.
601 /// This decreases the height by 1 and is the opposite of `push_internal_level`.
602 ///
603 /// Does not invalidate any handles or references pointing into the subtree
604 /// rooted at the first child of `self`.
605 ///
606 /// Panics if there is no internal level, i.e., if the root node is a leaf.
607 pub(super) fn pop_internal_level<A: Allocator + Clone>(&mut self, alloc: A) {
608 assert!(self.height > 0);
609
610 let top = self.node;
611
612 // SAFETY: we asserted to be internal.
613 let internal_self = unsafe { self.borrow_mut().cast_to_internal_unchecked() };
614 // SAFETY: we borrowed `self` exclusively and its borrow type is exclusive.
615 let internal_node = unsafe { &mut *NodeRef::as_internal_ptr(&internal_self) };
616 // SAFETY: the first edge is always initialized.
617 self.node = unsafe { internal_node.edges[0].assume_init_read() };
618 self.height -= 1;
619 self.clear_parent_link();
620
621 unsafe {
622 alloc.deallocate(top.cast(), Layout::new::<InternalNode<K, V>>());
623 }
624 }
625}
626
627impl<K, V, Type> NodeRef<marker::Owned, K, V, Type> {
628 /// Mutably borrows the owned root node. Unlike `reborrow_mut`, this is safe
629 /// because the return value cannot be used to destroy the root, and there
630 /// cannot be other references to the tree.
631 pub(super) fn borrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
632 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
633 }
634
635 /// Slightly mutably borrows the owned root node.
636 pub(super) fn borrow_valmut(&mut self) -> NodeRef<marker::ValMut<'_>, K, V, Type> {
637 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
638 }
639
640 /// Irreversibly transitions to a reference that permits traversal and offers
641 /// destructive methods and little else.
642 pub(super) fn into_dying(self) -> NodeRef<marker::Dying, K, V, Type> {
643 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
644 }
645}
646
647impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
648 /// Adds a key-value pair to the end of the node, and returns
649 /// a handle to the inserted value.
650 ///
651 /// # Safety
652 ///
653 /// The returned handle has an unbound lifetime.
654 pub(super) unsafe fn push_with_handle<'b>(
655 &mut self,
656 key: K,
657 val: V,
658 ) -> Handle<NodeRef<marker::Mut<'b>, K, V, marker::Leaf>, marker::KV> {
659 let len = self.len_mut();
660 let idx = usize::from(*len);
661 assert!(idx < CAPACITY);
662 *len += 1;
663 unsafe {
664 self.key_area_mut(idx).write(key);
665 self.val_area_mut(idx).write(val);
666 Handle::new_kv(
667 NodeRef { height: self.height, node: self.node, _marker: PhantomData },
668 idx,
669 )
670 }
671 }
672
673 /// Adds a key-value pair to the end of the node, and returns
674 /// the mutable reference of the inserted value.
675 pub(super) fn push(&mut self, key: K, val: V) -> *mut V {
676 // SAFETY: The unbound handle is no longer accessible.
677 unsafe { self.push_with_handle(key, val).into_val_mut() }
678 }
679}
680
681impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
682 /// Adds a key-value pair, and an edge to go to the right of that pair,
683 /// to the end of the node.
684 pub(super) fn push(&mut self, key: K, val: V, edge: Root<K, V>) {
685 assert!(edge.height == self.height - 1);
686
687 let len: &mut u16 = self.len_mut();
688 let idx: usize = usize::from(*len);
689 assert!(idx < CAPACITY);
690 *len += 1;
691 unsafe {
692 self.key_area_mut(idx).write(val:key);
693 self.val_area_mut(index:idx).write(val);
694 self.edge_area_mut(idx + 1).write(val:edge.node);
695 Handle::new_edge(self.reborrow_mut(), idx:idx + 1).correct_parent_link();
696 }
697 }
698}
699
700impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Leaf> {
701 /// Removes any static information asserting that this node is a `Leaf` node.
702 pub(super) fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
703 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
704 }
705}
706
707impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
708 /// Removes any static information asserting that this node is an `Internal` node.
709 pub(super) fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
710 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
711 }
712}
713
714impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
715 /// Checks whether a node is an `Internal` node or a `Leaf` node.
716 pub(super) fn force(
717 self,
718 ) -> ForceResult<
719 NodeRef<BorrowType, K, V, marker::Leaf>,
720 NodeRef<BorrowType, K, V, marker::Internal>,
721 > {
722 if self.height == 0 {
723 ForceResult::Leaf(NodeRef {
724 height: self.height,
725 node: self.node,
726 _marker: PhantomData,
727 })
728 } else {
729 ForceResult::Internal(NodeRef {
730 height: self.height,
731 node: self.node,
732 _marker: PhantomData,
733 })
734 }
735 }
736}
737
738impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
739 /// Unsafely asserts to the compiler the static information that this node is a `Leaf`.
740 pub(super) unsafe fn cast_to_leaf_unchecked(
741 self,
742 ) -> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
743 debug_assert!(self.height == 0);
744 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
745 }
746
747 /// Unsafely asserts to the compiler the static information that this node is an `Internal`.
748 unsafe fn cast_to_internal_unchecked(self) -> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
749 debug_assert!(self.height > 0);
750 NodeRef { height: self.height, node: self.node, _marker: PhantomData }
751 }
752}
753
754/// A reference to a specific key-value pair or edge within a node. The `Node` parameter
755/// must be a `NodeRef`, while the `Type` can either be `KV` (signifying a handle on a key-value
756/// pair) or `Edge` (signifying a handle on an edge).
757///
758/// Note that even `Leaf` nodes can have `Edge` handles. Instead of representing a pointer to
759/// a child node, these represent the spaces where child pointers would go between the key-value
760/// pairs. For example, in a node with length 2, there would be 3 possible edge locations - one
761/// to the left of the node, one between the two pairs, and one at the right of the node.
762pub(super) struct Handle<Node, Type> {
763 node: Node,
764 idx: usize,
765 _marker: PhantomData<Type>,
766}
767
768impl<Node: Copy, Type> Copy for Handle<Node, Type> {}
769// We don't need the full generality of `#[derive(Clone)]`, as the only time `Node` will be
770// `Clone`able is when it is an immutable reference and therefore `Copy`.
771impl<Node: Copy, Type> Clone for Handle<Node, Type> {
772 fn clone(&self) -> Self {
773 *self
774 }
775}
776
777impl<Node, Type> Handle<Node, Type> {
778 /// Retrieves the node that contains the edge or key-value pair this handle points to.
779 pub(super) fn into_node(self) -> Node {
780 self.node
781 }
782
783 /// Returns the position of this handle in the node.
784 pub(super) fn idx(&self) -> usize {
785 self.idx
786 }
787}
788
789impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV> {
790 /// Creates a new handle to a key-value pair in `node`.
791 /// Unsafe because the caller must ensure that `idx < node.len()`.
792 pub(super) unsafe fn new_kv(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
793 debug_assert!(idx < node.len());
794
795 Handle { node, idx, _marker: PhantomData }
796 }
797
798 pub(super) fn left_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
799 unsafe { Handle::new_edge(self.node, self.idx) }
800 }
801
802 pub(super) fn right_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
803 unsafe { Handle::new_edge(self.node, self.idx + 1) }
804 }
805}
806
807impl<BorrowType, K, V, NodeType, HandleType> PartialEq
808 for Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
809{
810 fn eq(&self, other: &Self) -> bool {
811 let Self { node: &NodeRef, idx: &usize, _marker: &PhantomData } = self;
812 node.eq(&other.node) && *idx == other.idx
813 }
814}
815
816impl<BorrowType, K, V, NodeType, HandleType>
817 Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
818{
819 /// Temporarily takes out another immutable handle on the same location.
820 pub(super) fn reborrow(
821 &self,
822 ) -> Handle<NodeRef<marker::Immut<'_>, K, V, NodeType>, HandleType> {
823 // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
824 Handle { node: self.node.reborrow(), idx: self.idx, _marker: PhantomData }
825 }
826}
827
828impl<'a, K, V, NodeType, HandleType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
829 /// Temporarily takes out another mutable handle on the same location. Beware, as
830 /// this method is very dangerous, doubly so since it might not immediately appear
831 /// dangerous.
832 ///
833 /// For details, see `NodeRef::reborrow_mut`.
834 pub(super) unsafe fn reborrow_mut(
835 &mut self,
836 ) -> Handle<NodeRef<marker::Mut<'_>, K, V, NodeType>, HandleType> {
837 // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
838 Handle { node: unsafe { self.node.reborrow_mut() }, idx: self.idx, _marker: PhantomData }
839 }
840
841 /// Returns a dormant copy of this handle which can be reawakened later.
842 ///
843 /// See `DormantMutRef` for more details.
844 pub(super) fn dormant(
845 &self,
846 ) -> Handle<NodeRef<marker::DormantMut, K, V, NodeType>, HandleType> {
847 Handle { node: self.node.dormant(), idx: self.idx, _marker: PhantomData }
848 }
849}
850
851impl<K, V, NodeType, HandleType> Handle<NodeRef<marker::DormantMut, K, V, NodeType>, HandleType> {
852 /// Revert to the unique borrow initially captured.
853 ///
854 /// # Safety
855 ///
856 /// The reborrow must have ended, i.e., the reference returned by `new` and
857 /// all pointers and references derived from it, must not be used anymore.
858 pub(super) unsafe fn awaken<'a>(
859 self,
860 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
861 Handle { node: unsafe { self.node.awaken() }, idx: self.idx, _marker: PhantomData }
862 }
863}
864
865impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
866 /// Creates a new handle to an edge in `node`.
867 /// Unsafe because the caller must ensure that `idx <= node.len()`.
868 pub(super) unsafe fn new_edge(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
869 debug_assert!(idx <= node.len());
870
871 Handle { node, idx, _marker: PhantomData }
872 }
873
874 pub(super) fn left_kv(
875 self,
876 ) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
877 if self.idx > 0 {
878 Ok(unsafe { Handle::new_kv(self.node, self.idx - 1) })
879 } else {
880 Err(self)
881 }
882 }
883
884 pub(super) fn right_kv(
885 self,
886 ) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
887 if self.idx < self.node.len() {
888 Ok(unsafe { Handle::new_kv(self.node, self.idx) })
889 } else {
890 Err(self)
891 }
892 }
893}
894
895pub(super) enum LeftOrRight<T> {
896 Left(T),
897 Right(T),
898}
899
900/// Given an edge index where we want to insert into a node filled to capacity,
901/// computes a sensible KV index of a split point and where to perform the insertion.
902/// The goal of the split point is for its key and value to end up in a parent node;
903/// the keys, values and edges to the left of the split point become the left child;
904/// the keys, values and edges to the right of the split point become the right child.
905fn splitpoint(edge_idx: usize) -> (usize, LeftOrRight<usize>) {
906 debug_assert!(edge_idx <= CAPACITY);
907 // Rust issue #74834 tries to explain these symmetric rules.
908 match edge_idx {
909 0..EDGE_IDX_LEFT_OF_CENTER => (KV_IDX_CENTER - 1, LeftOrRight::Left(edge_idx)),
910 EDGE_IDX_LEFT_OF_CENTER => (KV_IDX_CENTER, LeftOrRight::Left(edge_idx)),
911 EDGE_IDX_RIGHT_OF_CENTER => (KV_IDX_CENTER, LeftOrRight::Right(0)),
912 _ => (KV_IDX_CENTER + 1, LeftOrRight::Right(edge_idx - (KV_IDX_CENTER + 1 + 1))),
913 }
914}
915
916impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
917 /// Inserts a new key-value pair between the key-value pairs to the right and left of
918 /// this edge. This method assumes that there is enough space in the node for the new
919 /// pair to fit.
920 unsafe fn insert_fit(
921 mut self,
922 key: K,
923 val: V,
924 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
925 debug_assert!(self.node.len() < CAPACITY);
926 let new_len: usize = self.node.len() + 1;
927
928 unsafe {
929 slice_insert(self.node.key_area_mut(..new_len), self.idx, val:key);
930 slice_insert(self.node.val_area_mut(..new_len), self.idx, val);
931 *self.node.len_mut() = new_len as u16;
932
933 Handle::new_kv(self.node, self.idx)
934 }
935 }
936}
937
938impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
939 /// Inserts a new key-value pair between the key-value pairs to the right and left of
940 /// this edge. This method splits the node if there isn't enough room.
941 ///
942 /// Returns a dormant handle to the inserted node which can be reawakened
943 /// once splitting is complete.
944 fn insert<A: Allocator + Clone>(
945 self,
946 key: K,
947 val: V,
948 alloc: A,
949 ) -> (
950 Option<SplitResult<'a, K, V, marker::Leaf>>,
951 Handle<NodeRef<marker::DormantMut, K, V, marker::Leaf>, marker::KV>,
952 ) {
953 if self.node.len() < CAPACITY {
954 // SAFETY: There is enough space in the node for insertion.
955 let handle = unsafe { self.insert_fit(key, val) };
956 (None, handle.dormant())
957 } else {
958 let (middle_kv_idx, insertion) = splitpoint(self.idx);
959 let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
960 let mut result = middle.split(alloc);
961 let insertion_edge = match insertion {
962 LeftOrRight::Left(insert_idx) => unsafe {
963 Handle::new_edge(result.left.reborrow_mut(), insert_idx)
964 },
965 LeftOrRight::Right(insert_idx) => unsafe {
966 Handle::new_edge(result.right.borrow_mut(), insert_idx)
967 },
968 };
969 // SAFETY: We just split the node, so there is enough space for
970 // insertion.
971 let handle = unsafe { insertion_edge.insert_fit(key, val).dormant() };
972 (Some(result), handle)
973 }
974 }
975}
976
977impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
978 /// Fixes the parent pointer and index in the child node that this edge
979 /// links to. This is useful when the ordering of edges has been changed,
980 fn correct_parent_link(self) {
981 // Create backpointer without invalidating other references to the node.
982 let ptr: NonNull> = unsafe { NonNull::new_unchecked(ptr:NodeRef::as_internal_ptr(&self.node)) };
983 let idx: usize = self.idx;
984 let mut child: NodeRef, K, V, LeafOrInternal> = self.descend();
985 child.set_parent_link(parent:ptr, idx);
986 }
987}
988
989impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
990 /// Inserts a new key-value pair and an edge that will go to the right of that new pair
991 /// between this edge and the key-value pair to the right of this edge. This method assumes
992 /// that there is enough space in the node for the new pair to fit.
993 fn insert_fit(&mut self, key: K, val: V, edge: Root<K, V>) {
994 debug_assert!(self.node.len() < CAPACITY);
995 debug_assert!(edge.height == self.node.height - 1);
996 let new_len = self.node.len() + 1;
997
998 unsafe {
999 slice_insert(self.node.key_area_mut(..new_len), self.idx, key);
1000 slice_insert(self.node.val_area_mut(..new_len), self.idx, val);
1001 slice_insert(self.node.edge_area_mut(..new_len + 1), self.idx + 1, edge.node);
1002 *self.node.len_mut() = new_len as u16;
1003
1004 self.node.correct_childrens_parent_links(self.idx + 1..new_len + 1);
1005 }
1006 }
1007
1008 /// Inserts a new key-value pair and an edge that will go to the right of that new pair
1009 /// between this edge and the key-value pair to the right of this edge. This method splits
1010 /// the node if there isn't enough room.
1011 fn insert<A: Allocator + Clone>(
1012 mut self,
1013 key: K,
1014 val: V,
1015 edge: Root<K, V>,
1016 alloc: A,
1017 ) -> Option<SplitResult<'a, K, V, marker::Internal>> {
1018 assert!(edge.height == self.node.height - 1);
1019
1020 if self.node.len() < CAPACITY {
1021 self.insert_fit(key, val, edge);
1022 None
1023 } else {
1024 let (middle_kv_idx, insertion) = splitpoint(self.idx);
1025 let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
1026 let mut result = middle.split(alloc);
1027 let mut insertion_edge = match insertion {
1028 LeftOrRight::Left(insert_idx) => unsafe {
1029 Handle::new_edge(result.left.reborrow_mut(), insert_idx)
1030 },
1031 LeftOrRight::Right(insert_idx) => unsafe {
1032 Handle::new_edge(result.right.borrow_mut(), insert_idx)
1033 },
1034 };
1035 insertion_edge.insert_fit(key, val, edge);
1036 Some(result)
1037 }
1038 }
1039}
1040
1041impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
1042 /// Inserts a new key-value pair between the key-value pairs to the right and left of
1043 /// this edge. This method splits the node if there isn't enough room, and tries to
1044 /// insert the split off portion into the parent node recursively, until the root is reached.
1045 ///
1046 /// If the returned result is some `SplitResult`, the `left` field will be the root node.
1047 /// The returned pointer points to the inserted value, which in the case of `SplitResult`
1048 /// is in the `left` or `right` tree.
1049 pub(super) fn insert_recursing<A: Allocator + Clone>(
1050 self,
1051 key: K,
1052 value: V,
1053 alloc: A,
1054 split_root: impl FnOnce(SplitResult<'a, K, V, marker::LeafOrInternal>),
1055 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
1056 let (mut split, handle) = match self.insert(key, value, alloc.clone()) {
1057 // SAFETY: we have finished splitting and can now re-awaken the
1058 // handle to the inserted element.
1059 (None, handle) => return unsafe { handle.awaken() },
1060 (Some(split), handle) => (split.forget_node_type(), handle),
1061 };
1062
1063 loop {
1064 split = match split.left.ascend() {
1065 Ok(parent) => {
1066 match parent.insert(split.kv.0, split.kv.1, split.right, alloc.clone()) {
1067 // SAFETY: we have finished splitting and can now re-awaken the
1068 // handle to the inserted element.
1069 None => return unsafe { handle.awaken() },
1070 Some(split) => split.forget_node_type(),
1071 }
1072 }
1073 Err(root) => {
1074 split_root(SplitResult { left: root, ..split });
1075 // SAFETY: we have finished splitting and can now re-awaken the
1076 // handle to the inserted element.
1077 return unsafe { handle.awaken() };
1078 }
1079 };
1080 }
1081 }
1082}
1083
1084impl<BorrowType: marker::BorrowType, K, V>
1085 Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>
1086{
1087 /// Finds the node pointed to by this edge.
1088 ///
1089 /// The method name assumes you picture trees with the root node on top.
1090 ///
1091 /// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
1092 /// both, upon success, do nothing.
1093 pub(super) fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
1094 const {
1095 assert!(BorrowType::TRAVERSAL_PERMIT);
1096 }
1097
1098 // We need to use raw pointers to nodes because, if BorrowType is
1099 // marker::ValMut, there might be outstanding mutable references to
1100 // values that we must not invalidate. There's no worry accessing the
1101 // height field because that value is copied. Beware that, once the
1102 // node pointer is dereferenced, we access the edges array with a
1103 // reference (Rust issue #73987) and invalidate any other references
1104 // to or inside the array, should any be around.
1105 let parent_ptr: *mut InternalNode = NodeRef::as_internal_ptr(&self.node);
1106 let node: NonNull> = unsafe { (*parent_ptr).edges.get_unchecked(self.idx).assume_init_read() };
1107 NodeRef { node, height: self.node.height - 1, _marker: PhantomData }
1108 }
1109}
1110
1111impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Immut<'a>, K, V, NodeType>, marker::KV> {
1112 pub(super) fn into_kv(self) -> (&'a K, &'a V) {
1113 debug_assert!(self.idx < self.node.len());
1114 let leaf: &LeafNode = self.node.into_leaf();
1115 let k: &K = unsafe { leaf.keys.get_unchecked(self.idx).assume_init_ref() };
1116 let v: &V = unsafe { leaf.vals.get_unchecked(self.idx).assume_init_ref() };
1117 (k, v)
1118 }
1119}
1120
1121impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
1122 pub(super) fn key_mut(&mut self) -> &mut K {
1123 unsafe { self.node.key_area_mut(self.idx).assume_init_mut() }
1124 }
1125
1126 pub(super) fn into_val_mut(self) -> &'a mut V {
1127 debug_assert!(self.idx < self.node.len());
1128 let leaf: &mut LeafNode = self.node.into_leaf_mut();
1129 unsafe { leaf.vals.get_unchecked_mut(self.idx).assume_init_mut() }
1130 }
1131
1132 pub(super) fn into_kv_mut(self) -> (&'a mut K, &'a mut V) {
1133 debug_assert!(self.idx < self.node.len());
1134 let leaf: &mut LeafNode = self.node.into_leaf_mut();
1135 let k: &mut K = unsafe { leaf.keys.get_unchecked_mut(self.idx).assume_init_mut() };
1136 let v: &mut V = unsafe { leaf.vals.get_unchecked_mut(self.idx).assume_init_mut() };
1137 (k, v)
1138 }
1139}
1140
1141impl<'a, K, V, NodeType> Handle<NodeRef<marker::ValMut<'a>, K, V, NodeType>, marker::KV> {
1142 pub(super) fn into_kv_valmut(self) -> (&'a K, &'a mut V) {
1143 unsafe { self.node.into_key_val_mut_at(self.idx) }
1144 }
1145}
1146
1147impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
1148 pub(super) fn kv_mut(&mut self) -> (&mut K, &mut V) {
1149 debug_assert!(self.idx < self.node.len());
1150 // We cannot call separate key and value methods, because calling the second one
1151 // invalidates the reference returned by the first.
1152 unsafe {
1153 let leaf: &mut LeafNode = self.node.as_leaf_mut();
1154 let key: &mut K = leaf.keys.get_unchecked_mut(self.idx).assume_init_mut();
1155 let val: &mut V = leaf.vals.get_unchecked_mut(self.idx).assume_init_mut();
1156 (key, val)
1157 }
1158 }
1159
1160 /// Replaces the key and value that the KV handle refers to.
1161 pub(super) fn replace_kv(&mut self, k: K, v: V) -> (K, V) {
1162 let (key: &mut K, val: &mut V) = self.kv_mut();
1163 (mem::replace(dest:key, src:k), mem::replace(dest:val, src:v))
1164 }
1165}
1166
1167impl<K, V, NodeType> Handle<NodeRef<marker::Dying, K, V, NodeType>, marker::KV> {
1168 /// Extracts the key and value that the KV handle refers to.
1169 /// # Safety
1170 /// The node that the handle refers to must not yet have been deallocated.
1171 pub(super) unsafe fn into_key_val(mut self) -> (K, V) {
1172 debug_assert!(self.idx < self.node.len());
1173 let leaf = self.node.as_leaf_dying();
1174 unsafe {
1175 let key = leaf.keys.get_unchecked_mut(self.idx).assume_init_read();
1176 let val = leaf.vals.get_unchecked_mut(self.idx).assume_init_read();
1177 (key, val)
1178 }
1179 }
1180
1181 /// Drops the key and value that the KV handle refers to.
1182 /// # Safety
1183 /// The node that the handle refers to must not yet have been deallocated.
1184 #[inline]
1185 pub(super) unsafe fn drop_key_val(mut self) {
1186 // Run the destructor of the value even if the destructor of the key panics.
1187 struct Dropper<'a, T>(&'a mut MaybeUninit<T>);
1188 impl<T> Drop for Dropper<'_, T> {
1189 #[inline]
1190 fn drop(&mut self) {
1191 unsafe {
1192 self.0.assume_init_drop();
1193 }
1194 }
1195 }
1196
1197 debug_assert!(self.idx < self.node.len());
1198 let leaf = self.node.as_leaf_dying();
1199 unsafe {
1200 let key = leaf.keys.get_unchecked_mut(self.idx);
1201 let val = leaf.vals.get_unchecked_mut(self.idx);
1202 let _guard = Dropper(val);
1203 key.assume_init_drop();
1204 // dropping the guard will drop the value
1205 }
1206 }
1207}
1208
1209impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
1210 /// Helps implementations of `split` for a particular `NodeType`,
1211 /// by taking care of leaf data.
1212 fn split_leaf_data(&mut self, new_node: &mut LeafNode<K, V>) -> (K, V) {
1213 debug_assert!(self.idx < self.node.len());
1214 let old_len = self.node.len();
1215 let new_len = old_len - self.idx - 1;
1216 new_node.len = new_len as u16;
1217 unsafe {
1218 let k = self.node.key_area_mut(self.idx).assume_init_read();
1219 let v = self.node.val_area_mut(self.idx).assume_init_read();
1220
1221 move_to_slice(
1222 self.node.key_area_mut(self.idx + 1..old_len),
1223 &mut new_node.keys[..new_len],
1224 );
1225 move_to_slice(
1226 self.node.val_area_mut(self.idx + 1..old_len),
1227 &mut new_node.vals[..new_len],
1228 );
1229
1230 *self.node.len_mut() = self.idx as u16;
1231 (k, v)
1232 }
1233 }
1234}
1235
1236impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
1237 /// Splits the underlying node into three parts:
1238 ///
1239 /// - The node is truncated to only contain the key-value pairs to the left of
1240 /// this handle.
1241 /// - The key and value pointed to by this handle are extracted.
1242 /// - All the key-value pairs to the right of this handle are put into a newly
1243 /// allocated node.
1244 pub(super) fn split<A: Allocator + Clone>(
1245 mut self,
1246 alloc: A,
1247 ) -> SplitResult<'a, K, V, marker::Leaf> {
1248 let mut new_node = LeafNode::new(alloc);
1249
1250 let kv = self.split_leaf_data(&mut new_node);
1251
1252 let right = NodeRef::from_new_leaf(new_node);
1253 SplitResult { left: self.node, kv, right }
1254 }
1255
1256 /// Removes the key-value pair pointed to by this handle and returns it, along with the edge
1257 /// that the key-value pair collapsed into.
1258 pub(super) fn remove(
1259 mut self,
1260 ) -> ((K, V), Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>) {
1261 let old_len = self.node.len();
1262 unsafe {
1263 let k = slice_remove(self.node.key_area_mut(..old_len), self.idx);
1264 let v = slice_remove(self.node.val_area_mut(..old_len), self.idx);
1265 *self.node.len_mut() = (old_len - 1) as u16;
1266 ((k, v), self.left_edge())
1267 }
1268 }
1269}
1270
1271impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> {
1272 /// Splits the underlying node into three parts:
1273 ///
1274 /// - The node is truncated to only contain the edges and key-value pairs to the
1275 /// left of this handle.
1276 /// - The key and value pointed to by this handle are extracted.
1277 /// - All the edges and key-value pairs to the right of this handle are put into
1278 /// a newly allocated node.
1279 pub(super) fn split<A: Allocator + Clone>(
1280 mut self,
1281 alloc: A,
1282 ) -> SplitResult<'a, K, V, marker::Internal> {
1283 let old_len = self.node.len();
1284 unsafe {
1285 let mut new_node = InternalNode::new(alloc);
1286 let kv = self.split_leaf_data(&mut new_node.data);
1287 let new_len = usize::from(new_node.data.len);
1288 move_to_slice(
1289 self.node.edge_area_mut(self.idx + 1..old_len + 1),
1290 &mut new_node.edges[..new_len + 1],
1291 );
1292
1293 let height = self.node.height;
1294 let right = NodeRef::from_new_internal(new_node, height);
1295
1296 SplitResult { left: self.node, kv, right }
1297 }
1298 }
1299}
1300
1301/// Represents a session for evaluating and performing a balancing operation
1302/// around an internal key-value pair.
1303pub(super) struct BalancingContext<'a, K, V> {
1304 parent: Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV>,
1305 left_child: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1306 right_child: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1307}
1308
1309impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> {
1310 pub(super) fn consider_for_balancing(self) -> BalancingContext<'a, K, V> {
1311 let self1: Handle, K, …, …>, …> = unsafe { ptr::read(&self) };
1312 let self2: Handle, K, …, …>, …> = unsafe { ptr::read(&self) };
1313 BalancingContext {
1314 parent: self,
1315 left_child: self1.left_edge().descend(),
1316 right_child: self2.right_edge().descend(),
1317 }
1318 }
1319}
1320
1321impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1322 /// Chooses a balancing context involving the node as a child, thus between
1323 /// the KV immediately to the left or to the right in the parent node.
1324 /// Returns an `Err` if there is no parent.
1325 /// Panics if the parent is empty.
1326 ///
1327 /// Prefers the left side, to be optimal if the given node is somehow
1328 /// underfull, meaning here only that it has fewer elements than its left
1329 /// sibling and than its right sibling, if they exist. In that case,
1330 /// merging with the left sibling is faster, since we only need to move
1331 /// the node's N elements, instead of shifting them to the right and moving
1332 /// more than N elements in front. Stealing from the left sibling is also
1333 /// typically faster, since we only need to shift the node's N elements to
1334 /// the right, instead of shifting at least N of the sibling's elements to
1335 /// the left.
1336 pub(super) fn choose_parent_kv(self) -> Result<LeftOrRight<BalancingContext<'a, K, V>>, Self> {
1337 match unsafe { ptr::read(&self) }.ascend() {
1338 Ok(parent_edge) => match parent_edge.left_kv() {
1339 Ok(left_parent_kv) => Ok(LeftOrRight::Left(BalancingContext {
1340 parent: unsafe { ptr::read(&left_parent_kv) },
1341 left_child: left_parent_kv.left_edge().descend(),
1342 right_child: self,
1343 })),
1344 Err(parent_edge) => match parent_edge.right_kv() {
1345 Ok(right_parent_kv) => Ok(LeftOrRight::Right(BalancingContext {
1346 parent: unsafe { ptr::read(&right_parent_kv) },
1347 left_child: self,
1348 right_child: right_parent_kv.right_edge().descend(),
1349 })),
1350 Err(_) => unreachable!("empty internal node"),
1351 },
1352 },
1353 Err(root) => Err(root),
1354 }
1355 }
1356}
1357
1358impl<'a, K, V> BalancingContext<'a, K, V> {
1359 pub(super) fn left_child_len(&self) -> usize {
1360 self.left_child.len()
1361 }
1362
1363 pub(super) fn right_child_len(&self) -> usize {
1364 self.right_child.len()
1365 }
1366
1367 pub(super) fn into_left_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1368 self.left_child
1369 }
1370
1371 pub(super) fn into_right_child(self) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1372 self.right_child
1373 }
1374
1375 /// Returns whether merging is possible, i.e., whether there is enough room
1376 /// in a node to combine the central KV with both adjacent child nodes.
1377 pub(super) fn can_merge(&self) -> bool {
1378 self.left_child.len() + 1 + self.right_child.len() <= CAPACITY
1379 }
1380}
1381
1382impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
1383 /// Performs a merge and lets a closure decide what to return.
1384 fn do_merge<
1385 F: FnOnce(
1386 NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
1387 NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1388 ) -> R,
1389 R,
1390 A: Allocator,
1391 >(
1392 self,
1393 result: F,
1394 alloc: A,
1395 ) -> R {
1396 let Handle { node: mut parent_node, idx: parent_idx, _marker } = self.parent;
1397 let old_parent_len = parent_node.len();
1398 let mut left_node = self.left_child;
1399 let old_left_len = left_node.len();
1400 let mut right_node = self.right_child;
1401 let right_len = right_node.len();
1402 let new_left_len = old_left_len + 1 + right_len;
1403
1404 assert!(new_left_len <= CAPACITY);
1405
1406 unsafe {
1407 *left_node.len_mut() = new_left_len as u16;
1408
1409 let parent_key = slice_remove(parent_node.key_area_mut(..old_parent_len), parent_idx);
1410 left_node.key_area_mut(old_left_len).write(parent_key);
1411 move_to_slice(
1412 right_node.key_area_mut(..right_len),
1413 left_node.key_area_mut(old_left_len + 1..new_left_len),
1414 );
1415
1416 let parent_val = slice_remove(parent_node.val_area_mut(..old_parent_len), parent_idx);
1417 left_node.val_area_mut(old_left_len).write(parent_val);
1418 move_to_slice(
1419 right_node.val_area_mut(..right_len),
1420 left_node.val_area_mut(old_left_len + 1..new_left_len),
1421 );
1422
1423 slice_remove(&mut parent_node.edge_area_mut(..old_parent_len + 1), parent_idx + 1);
1424 parent_node.correct_childrens_parent_links(parent_idx + 1..old_parent_len);
1425 *parent_node.len_mut() -= 1;
1426
1427 if parent_node.height > 1 {
1428 // SAFETY: the height of the nodes being merged is one below the height
1429 // of the node of this edge, thus above zero, so they are internal.
1430 let mut left_node = left_node.reborrow_mut().cast_to_internal_unchecked();
1431 let mut right_node = right_node.cast_to_internal_unchecked();
1432 move_to_slice(
1433 right_node.edge_area_mut(..right_len + 1),
1434 left_node.edge_area_mut(old_left_len + 1..new_left_len + 1),
1435 );
1436
1437 left_node.correct_childrens_parent_links(old_left_len + 1..new_left_len + 1);
1438
1439 alloc.deallocate(right_node.node.cast(), Layout::new::<InternalNode<K, V>>());
1440 } else {
1441 alloc.deallocate(right_node.node.cast(), Layout::new::<LeafNode<K, V>>());
1442 }
1443 }
1444 result(parent_node, left_node)
1445 }
1446
1447 /// Merges the parent's key-value pair and both adjacent child nodes into
1448 /// the left child node and returns the shrunk parent node.
1449 ///
1450 /// Panics unless we `.can_merge()`.
1451 pub(super) fn merge_tracking_parent<A: Allocator + Clone>(
1452 self,
1453 alloc: A,
1454 ) -> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
1455 self.do_merge(|parent, _child| parent, alloc)
1456 }
1457
1458 /// Merges the parent's key-value pair and both adjacent child nodes into
1459 /// the left child node and returns that child node.
1460 ///
1461 /// Panics unless we `.can_merge()`.
1462 pub(super) fn merge_tracking_child<A: Allocator + Clone>(
1463 self,
1464 alloc: A,
1465 ) -> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
1466 self.do_merge(|_parent, child| child, alloc)
1467 }
1468
1469 /// Merges the parent's key-value pair and both adjacent child nodes into
1470 /// the left child node and returns the edge handle in that child node
1471 /// where the tracked child edge ended up,
1472 ///
1473 /// Panics unless we `.can_merge()`.
1474 pub(super) fn merge_tracking_child_edge<A: Allocator + Clone>(
1475 self,
1476 track_edge_idx: LeftOrRight<usize>,
1477 alloc: A,
1478 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1479 let old_left_len = self.left_child.len();
1480 let right_len = self.right_child.len();
1481 assert!(match track_edge_idx {
1482 LeftOrRight::Left(idx) => idx <= old_left_len,
1483 LeftOrRight::Right(idx) => idx <= right_len,
1484 });
1485 let child = self.merge_tracking_child(alloc);
1486 let new_idx = match track_edge_idx {
1487 LeftOrRight::Left(idx) => idx,
1488 LeftOrRight::Right(idx) => old_left_len + 1 + idx,
1489 };
1490 unsafe { Handle::new_edge(child, new_idx) }
1491 }
1492
1493 /// Removes a key-value pair from the left child and places it in the key-value storage
1494 /// of the parent, while pushing the old parent key-value pair into the right child.
1495 /// Returns a handle to the edge in the right child corresponding to where the original
1496 /// edge specified by `track_right_edge_idx` ended up.
1497 pub(super) fn steal_left(
1498 mut self,
1499 track_right_edge_idx: usize,
1500 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1501 self.bulk_steal_left(1);
1502 unsafe { Handle::new_edge(self.right_child, 1 + track_right_edge_idx) }
1503 }
1504
1505 /// Removes a key-value pair from the right child and places it in the key-value storage
1506 /// of the parent, while pushing the old parent key-value pair onto the left child.
1507 /// Returns a handle to the edge in the left child specified by `track_left_edge_idx`,
1508 /// which didn't move.
1509 pub(super) fn steal_right(
1510 mut self,
1511 track_left_edge_idx: usize,
1512 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1513 self.bulk_steal_right(1);
1514 unsafe { Handle::new_edge(self.left_child, track_left_edge_idx) }
1515 }
1516
1517 /// This does stealing similar to `steal_left` but steals multiple elements at once.
1518 pub(super) fn bulk_steal_left(&mut self, count: usize) {
1519 assert!(count > 0);
1520 unsafe {
1521 let left_node = &mut self.left_child;
1522 let old_left_len = left_node.len();
1523 let right_node = &mut self.right_child;
1524 let old_right_len = right_node.len();
1525
1526 // Make sure that we may steal safely.
1527 assert!(old_right_len + count <= CAPACITY);
1528 assert!(old_left_len >= count);
1529
1530 let new_left_len = old_left_len - count;
1531 let new_right_len = old_right_len + count;
1532 *left_node.len_mut() = new_left_len as u16;
1533 *right_node.len_mut() = new_right_len as u16;
1534
1535 // Move leaf data.
1536 {
1537 // Make room for stolen elements in the right child.
1538 slice_shr(right_node.key_area_mut(..new_right_len), count);
1539 slice_shr(right_node.val_area_mut(..new_right_len), count);
1540
1541 // Move elements from the left child to the right one.
1542 move_to_slice(
1543 left_node.key_area_mut(new_left_len + 1..old_left_len),
1544 right_node.key_area_mut(..count - 1),
1545 );
1546 move_to_slice(
1547 left_node.val_area_mut(new_left_len + 1..old_left_len),
1548 right_node.val_area_mut(..count - 1),
1549 );
1550
1551 // Move the leftmost stolen pair to the parent.
1552 let k = left_node.key_area_mut(new_left_len).assume_init_read();
1553 let v = left_node.val_area_mut(new_left_len).assume_init_read();
1554 let (k, v) = self.parent.replace_kv(k, v);
1555
1556 // Move parent's key-value pair to the right child.
1557 right_node.key_area_mut(count - 1).write(k);
1558 right_node.val_area_mut(count - 1).write(v);
1559 }
1560
1561 match (left_node.reborrow_mut().force(), right_node.reborrow_mut().force()) {
1562 (ForceResult::Internal(mut left), ForceResult::Internal(mut right)) => {
1563 // Make room for stolen edges.
1564 slice_shr(right.edge_area_mut(..new_right_len + 1), count);
1565
1566 // Steal edges.
1567 move_to_slice(
1568 left.edge_area_mut(new_left_len + 1..old_left_len + 1),
1569 right.edge_area_mut(..count),
1570 );
1571
1572 right.correct_childrens_parent_links(0..new_right_len + 1);
1573 }
1574 (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
1575 _ => unreachable!(),
1576 }
1577 }
1578 }
1579
1580 /// The symmetric clone of `bulk_steal_left`.
1581 pub(super) fn bulk_steal_right(&mut self, count: usize) {
1582 assert!(count > 0);
1583 unsafe {
1584 let left_node = &mut self.left_child;
1585 let old_left_len = left_node.len();
1586 let right_node = &mut self.right_child;
1587 let old_right_len = right_node.len();
1588
1589 // Make sure that we may steal safely.
1590 assert!(old_left_len + count <= CAPACITY);
1591 assert!(old_right_len >= count);
1592
1593 let new_left_len = old_left_len + count;
1594 let new_right_len = old_right_len - count;
1595 *left_node.len_mut() = new_left_len as u16;
1596 *right_node.len_mut() = new_right_len as u16;
1597
1598 // Move leaf data.
1599 {
1600 // Move the rightmost stolen pair to the parent.
1601 let k = right_node.key_area_mut(count - 1).assume_init_read();
1602 let v = right_node.val_area_mut(count - 1).assume_init_read();
1603 let (k, v) = self.parent.replace_kv(k, v);
1604
1605 // Move parent's key-value pair to the left child.
1606 left_node.key_area_mut(old_left_len).write(k);
1607 left_node.val_area_mut(old_left_len).write(v);
1608
1609 // Move elements from the right child to the left one.
1610 move_to_slice(
1611 right_node.key_area_mut(..count - 1),
1612 left_node.key_area_mut(old_left_len + 1..new_left_len),
1613 );
1614 move_to_slice(
1615 right_node.val_area_mut(..count - 1),
1616 left_node.val_area_mut(old_left_len + 1..new_left_len),
1617 );
1618
1619 // Fill gap where stolen elements used to be.
1620 slice_shl(right_node.key_area_mut(..old_right_len), count);
1621 slice_shl(right_node.val_area_mut(..old_right_len), count);
1622 }
1623
1624 match (left_node.reborrow_mut().force(), right_node.reborrow_mut().force()) {
1625 (ForceResult::Internal(mut left), ForceResult::Internal(mut right)) => {
1626 // Steal edges.
1627 move_to_slice(
1628 right.edge_area_mut(..count),
1629 left.edge_area_mut(old_left_len + 1..new_left_len + 1),
1630 );
1631
1632 // Fill gap where stolen edges used to be.
1633 slice_shl(right.edge_area_mut(..old_right_len + 1), count);
1634
1635 left.correct_childrens_parent_links(old_left_len + 1..new_left_len + 1);
1636 right.correct_childrens_parent_links(0..new_right_len + 1);
1637 }
1638 (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
1639 _ => unreachable!(),
1640 }
1641 }
1642 }
1643}
1644
1645impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
1646 pub(super) fn forget_node_type(
1647 self,
1648 ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
1649 unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
1650 }
1651}
1652
1653impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge> {
1654 pub(super) fn forget_node_type(
1655 self,
1656 ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
1657 unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
1658 }
1659}
1660
1661impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::KV> {
1662 pub(super) fn forget_node_type(
1663 self,
1664 ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV> {
1665 unsafe { Handle::new_kv(self.node.forget_type(), self.idx) }
1666 }
1667}
1668
1669impl<BorrowType, K, V, Type> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, Type> {
1670 /// Checks whether the underlying node is an `Internal` node or a `Leaf` node.
1671 pub(super) fn force(
1672 self,
1673 ) -> ForceResult<
1674 Handle<NodeRef<BorrowType, K, V, marker::Leaf>, Type>,
1675 Handle<NodeRef<BorrowType, K, V, marker::Internal>, Type>,
1676 > {
1677 match self.node.force() {
1678 ForceResult::Leaf(node: NodeRef) => {
1679 ForceResult::Leaf(Handle { node, idx: self.idx, _marker: PhantomData })
1680 }
1681 ForceResult::Internal(node: NodeRef) => {
1682 ForceResult::Internal(Handle { node, idx: self.idx, _marker: PhantomData })
1683 }
1684 }
1685 }
1686}
1687
1688impl<'a, K, V, Type> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, Type> {
1689 /// Unsafely asserts to the compiler the static information that the handle's node is a `Leaf`.
1690 pub(super) unsafe fn cast_to_leaf_unchecked(
1691 self,
1692 ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, Type> {
1693 let node: NodeRef, K, V, Leaf> = unsafe { self.node.cast_to_leaf_unchecked() };
1694 Handle { node, idx: self.idx, _marker: PhantomData }
1695 }
1696}
1697
1698impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
1699 /// Move the suffix after `self` from one node to another one. `right` must be empty.
1700 /// The first edge of `right` remains unchanged.
1701 pub(super) fn move_suffix(
1702 &mut self,
1703 right: &mut NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
1704 ) {
1705 unsafe {
1706 let new_left_len = self.idx;
1707 let mut left_node = self.reborrow_mut().into_node();
1708 let old_left_len = left_node.len();
1709
1710 let new_right_len = old_left_len - new_left_len;
1711 let mut right_node = right.reborrow_mut();
1712
1713 assert!(right_node.len() == 0);
1714 assert!(left_node.height == right_node.height);
1715
1716 if new_right_len > 0 {
1717 *left_node.len_mut() = new_left_len as u16;
1718 *right_node.len_mut() = new_right_len as u16;
1719
1720 move_to_slice(
1721 left_node.key_area_mut(new_left_len..old_left_len),
1722 right_node.key_area_mut(..new_right_len),
1723 );
1724 move_to_slice(
1725 left_node.val_area_mut(new_left_len..old_left_len),
1726 right_node.val_area_mut(..new_right_len),
1727 );
1728 match (left_node.force(), right_node.force()) {
1729 (ForceResult::Internal(mut left), ForceResult::Internal(mut right)) => {
1730 move_to_slice(
1731 left.edge_area_mut(new_left_len + 1..old_left_len + 1),
1732 right.edge_area_mut(1..new_right_len + 1),
1733 );
1734 right.correct_childrens_parent_links(1..new_right_len + 1);
1735 }
1736 (ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
1737 _ => unreachable!(),
1738 }
1739 }
1740 }
1741 }
1742}
1743
1744pub(super) enum ForceResult<Leaf, Internal> {
1745 Leaf(Leaf),
1746 Internal(Internal),
1747}
1748
1749/// Result of insertion, when a node needed to expand beyond its capacity.
1750pub(super) struct SplitResult<'a, K, V, NodeType> {
1751 // Altered node in existing tree with elements and edges that belong to the left of `kv`.
1752 pub left: NodeRef<marker::Mut<'a>, K, V, NodeType>,
1753 // Some key and value that existed before and were split off, to be inserted elsewhere.
1754 pub kv: (K, V),
1755 // Owned, unattached, new node with elements and edges that belong to the right of `kv`.
1756 pub right: NodeRef<marker::Owned, K, V, NodeType>,
1757}
1758
1759impl<'a, K, V> SplitResult<'a, K, V, marker::Leaf> {
1760 pub(super) fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
1761 SplitResult { left: self.left.forget_type(), kv: self.kv, right: self.right.forget_type() }
1762 }
1763}
1764
1765impl<'a, K, V> SplitResult<'a, K, V, marker::Internal> {
1766 pub(super) fn forget_node_type(self) -> SplitResult<'a, K, V, marker::LeafOrInternal> {
1767 SplitResult { left: self.left.forget_type(), kv: self.kv, right: self.right.forget_type() }
1768 }
1769}
1770
1771pub(super) mod marker {
1772 use core::marker::PhantomData;
1773
1774 pub(crate) enum Leaf {}
1775 pub(crate) enum Internal {}
1776 pub(crate) enum LeafOrInternal {}
1777
1778 pub(crate) enum Owned {}
1779 pub(crate) enum Dying {}
1780 pub(crate) enum DormantMut {}
1781 pub(crate) struct Immut<'a>(PhantomData<&'a ()>);
1782 pub(crate) struct Mut<'a>(PhantomData<&'a mut ()>);
1783 pub(crate) struct ValMut<'a>(PhantomData<&'a mut ()>);
1784
1785 pub(crate) trait BorrowType {
1786 /// If node references of this borrow type allow traversing to other
1787 /// nodes in the tree, this constant is set to `true`. It can be used
1788 /// for a compile-time assertion.
1789 const TRAVERSAL_PERMIT: bool = true;
1790 }
1791 impl BorrowType for Owned {
1792 /// Reject traversal, because it isn't needed. Instead traversal
1793 /// happens using the result of `borrow_mut`.
1794 /// By disabling traversal, and only creating new references to roots,
1795 /// we know that every reference of the `Owned` type is to a root node.
1796 const TRAVERSAL_PERMIT: bool = false;
1797 }
1798 impl BorrowType for Dying {}
1799 impl<'a> BorrowType for Immut<'a> {}
1800 impl<'a> BorrowType for Mut<'a> {}
1801 impl<'a> BorrowType for ValMut<'a> {}
1802 impl BorrowType for DormantMut {}
1803
1804 pub(crate) enum KV {}
1805 pub(crate) enum Edge {}
1806}
1807
1808/// Inserts a value into a slice of initialized elements followed by one uninitialized element.
1809///
1810/// # Safety
1811/// The slice has more than `idx` elements.
1812unsafe fn slice_insert<T>(slice: &mut [MaybeUninit<T>], idx: usize, val: T) {
1813 unsafe {
1814 let len: usize = slice.len();
1815 debug_assert!(len > idx);
1816 let slice_ptr: *mut MaybeUninit = slice.as_mut_ptr();
1817 if len > idx + 1 {
1818 ptr::copy(src:slice_ptr.add(idx), dst:slice_ptr.add(idx + 1), count:len - idx - 1);
1819 }
1820 (*slice_ptr.add(count:idx)).write(val);
1821 }
1822}
1823
1824/// Removes and returns a value from a slice of all initialized elements, leaving behind one
1825/// trailing uninitialized element.
1826///
1827/// # Safety
1828/// The slice has more than `idx` elements.
1829unsafe fn slice_remove<T>(slice: &mut [MaybeUninit<T>], idx: usize) -> T {
1830 unsafe {
1831 let len: usize = slice.len();
1832 debug_assert!(idx < len);
1833 let slice_ptr: *mut MaybeUninit = slice.as_mut_ptr();
1834 let ret: T = (*slice_ptr.add(count:idx)).assume_init_read();
1835 ptr::copy(src:slice_ptr.add(idx + 1), dst:slice_ptr.add(idx), count:len - idx - 1);
1836 ret
1837 }
1838}
1839
1840/// Shifts the elements in a slice `distance` positions to the left.
1841///
1842/// # Safety
1843/// The slice has at least `distance` elements.
1844unsafe fn slice_shl<T>(slice: &mut [MaybeUninit<T>], distance: usize) {
1845 unsafe {
1846 let slice_ptr: *mut MaybeUninit = slice.as_mut_ptr();
1847 ptr::copy(src:slice_ptr.add(distance), dst:slice_ptr, count:slice.len() - distance);
1848 }
1849}
1850
1851/// Shifts the elements in a slice `distance` positions to the right.
1852///
1853/// # Safety
1854/// The slice has at least `distance` elements.
1855unsafe fn slice_shr<T>(slice: &mut [MaybeUninit<T>], distance: usize) {
1856 unsafe {
1857 let slice_ptr: *mut MaybeUninit = slice.as_mut_ptr();
1858 ptr::copy(src:slice_ptr, dst:slice_ptr.add(distance), count:slice.len() - distance);
1859 }
1860}
1861
1862/// Moves all values from a slice of initialized elements to a slice
1863/// of uninitialized elements, leaving behind `src` as all uninitialized.
1864/// Works like `dst.copy_from_slice(src)` but does not require `T` to be `Copy`.
1865fn move_to_slice<T>(src: &mut [MaybeUninit<T>], dst: &mut [MaybeUninit<T>]) {
1866 assert!(src.len() == dst.len());
1867 unsafe {
1868 ptr::copy_nonoverlapping(src.as_ptr(), dst.as_mut_ptr(), count:src.len());
1869 }
1870}
1871
1872#[cfg(test)]
1873mod tests;
1874