Quelle node.rs
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// This is an attempt at an implementation following the ideal
//
// ```
// struct BTreeMap<K, V> {
// height: usize,
// root: Option<Box<Node<K, V, height>>>
// }
//
// struct Node<K, V, height: usize> {
// keys: [K; 2 * B - 1],
// vals: [V; 2 * B - 1],
// edges: if height > 0 {
// [Box<Node<K, V, height - 1>>; 2 * B]
// } else { () },
// parent: *const Node<K, V, height + 1>,
// parent_idx: u16,
// len: u16,
// }
// ```
//
// Since Rust doesn't actually have dependent types and polymorphic recursion,
// we make do with lots of unsafety.
// A major goal of this module is to avoid complexity by treating the tree as a generic (if
// weirdly shaped) container and avoiding dealing with most of the B-Tree invariants. As such,
// this module doesn't care whether the entries are sorted, which nodes can be underfull, or
// even what underfull means. However, we do rely on a few invariants:
//
// - Trees must have uniform depth/height. This means that every path down to a leaf from a
// given node has exactly the same length.
// - A node of length `n` has `n` keys, `n` values, and (in an internal node) `n + 1` edges.
// This implies that even an empty internal node has at least one edge.
use core::marker::PhantomData;
use core::mem::{self, MaybeUninit};
use core::ptr::{self, NonNull, Unique};
use core::slice;
use crate::boxed::FallibleBox;
use crate::TryReserveError;
use alloc::alloc::{Allocator, Global, Layout};
use alloc::boxed::Box;
const B: usize = 6;
pub const MIN_LEN: usize = B - 1;
pub const CAPACITY: usize = 2 * B - 1;
/// The underlying representation of leaf nodes. Note that it is often unsafe to actually store
/// these, since only the first `len` keys and values are assumed to be initialized. As such,
/// these should always be put behind pointers, and specifically behind `BoxedNode` in the own ed
/// case.
///
/// We have a separate type for the header and rely on it matching the prefix of `LeafNode`, in
/// order to statically allocate a single dummy node to avoid allocations. This struct is
/// `repr(C)` to prevent them from being reordered. `LeafNode` does not just contain a
/// `NodeHeader` because we do not want unnecessary padding between `len` and the keys.
/// Crucially, `NodeHeader` can be safely transmuted to different K and V. (This is exploited
/// by `as_header`.)
/// See `into_key_slice` for an explanation of K2. K2 cannot be safely transmuted around
/// because the size of `NodeHeader` depends on its alignment!
#[repr(C)]
struct NodeHeader<K, V, K2 = ()> {
/// We use `*const` as opposed to `*mut` so as to be covariant in `K` and `V`.
/// This either points to an actual node or is null.
parent: *const InternalNode<K, V>,
/// This node's index into the parent node's `edges` array.
/// `*node.parent.edges[node.parent_idx]` should be the same thing as `node`.
/// This is only guaranteed to be initialized when `parent` is non-null.
parent_idx: MaybeUninit<u16>,
/// The number of keys and values this node stores.
///
/// This next to `parent_idx` to encourage the compiler to join `len` and
/// `parent_idx` into the same 32-bit word, reducing space overhead.
len: u16,
/// See `into_key_slice`.
keys_start: [K2; 0],
}
#[repr(C)]
struct LeafNode<K, V> {
/// We use `*const` as opposed to `*mut` so as to be covariant in `K` and `V`.
/// This either points to an actual node or is null.
parent: *const InternalNode<K, V>,
/// This node's index into the parent node's `edges` array.
/// `*node.parent.edges[node.parent_idx]` should be the same thing as `node`.
/// This is only guaranteed to be initialized when `parent` is non-null.
parent_idx: MaybeUninit<u16>,
/// The number of keys and values this node stores.
///
/// This next to `parent_idx` to encourage the compiler to join `len` and
/// `parent_idx` into the same 32-bit word, reducing space overhead.
len: u16,
/// The arrays storing the actual data of the node. Only the first `len` elements of each
/// array are initialized and valid.
keys: [MaybeUninit<K>; CAPACITY],
vals: [MaybeUninit<V>; CAPACITY],
}
impl<K, V> LeafNode<K, V> {
/// Creates a new `LeafNode`. Unsafe because all nodes should really be hidden behind
/// `BoxedNode`, preventing accidental dropping of uninitialized keys and values.
unsafe fn new() -> Self {
LeafNode {
// As a general policy, we leave fields uninitialized if they can be, as this should
// be both slightly faster and easier to track in Valgrind.
keys: MaybeUninit::uninit_array::<CAPACITY>(),
vals: MaybeUninit::uninit_array::<CAPACITY>(),
parent: ptr::null(),
parent_idx: MaybeUninit::uninit(),
len: 0,
}
}
}
impl<K, V> NodeHeader<K, V> {
fn is_shared_root(&self) -> bool {
ptr::eq(self, &EMPTY_ROOT_NODE as *const _ as *const _)
}
}
// We need to implement Sync here in order to make a static instance.
unsafe impl Sync for NodeHeader<(), ()> {}
// An empty node used as a placeholder for the root node, to avoid allocations.
// We use just a header in order to save space, since no operation on an empty tree will
// ever take a pointer past the first key.
static EMPTY_ROOT_NODE: NodeHeader<(), ()> = NodeHeader {
parent: ptr::null(),
parent_idx: MaybeUninit::uninit(),
len: 0,
keys_start: [],
};
/// The underlying representation of internal nodes. As with `LeafNode`s, these should be hidden
/// behind `BoxedNode`s to prevent dropping uninitialized keys and values. Any pointer to an
/// `InternalNode` can be directly casted to a pointer to the underlying `LeafNode` portion of the
/// node, allowing code to act on leaf and internal nodes generically without having to even check
/// which of the two a pointer is pointing at. This property is enabled by the use of `repr(C)`.
#[repr(C)]
struct InternalNode<K, V> {
data: LeafNode<K, V>,
/// The pointers to the children of this node. `len + 1` of these are considered
/// initialized and valid.
edges: [MaybeUninit<BoxedNode<K, V>>; 2 * B],
}
impl<K, V> InternalNode<K, V> {
/// Creates a new `InternalNode`.
///
/// This is unsafe for two reasons. First, it returns an `InternalNode` by value, risking
/// dropping of uninitialized fields. Second, an invariant of internal nodes is that `len + 1`
/// edges are initialized and valid, meaning that even when the node is empty (having a
/// `len` of 0), there must be one initialized and valid edge. This function does not set up
/// such an edge.
unsafe fn new() -> Self {
InternalNode {
data: LeafNode::new(),
edges: MaybeUninit::uninit_array::<{ 2 * B }>(),
}
}
}
/// An owned pointer to a node. This basically is either `Box<LeafNode<K, V>>` or
/// `Box<InternalNode<K, V>>`. However, it contains no information as to which of the two types
/// of nodes is actually behind the box, and, partially due to this lack of information, has no
/// destructor.
struct BoxedNode<K, V> {
ptr: Unique<LeafNode<K, V>>,
}
impl<K, V> BoxedNode<K, V> {
fn from_leaf(node: Box<LeafNode<K, V>>) -> Self {
let (ptr, _g) = Box::into_unique(node);
BoxedNode { ptr: ptr }
}
fn from_internal(node: Box<InternalNode<K, V>>) -> Self {
unsafe {
BoxedNode {
ptr: Unique::new_unchecked(Box::into_raw(node) as *mut LeafNode<K, V>),
}
}
}
unsafe fn from_ptr(ptr: NonNull<LeafNode<K, V>>) -> Self {
BoxedNode {
ptr: Unique::new_unchecked(ptr.as_ptr()),
}
}
fn as_ptr(&self) -> NonNull<LeafNode<K, V>> {
NonNull::from(self.ptr)
}
}
/// An owned tree. Note that despite being owned, this does not have a destructor,
/// and must be cleaned up manually.
pub struct Root<K, V> {
node: BoxedNode<K, V>,
height: usize,
}
unsafe impl<K: Sync, V: Sync> Sync for Root<K, V> {}
unsafe impl<K: Send, V: Send> Send for Root<K, V> {}
impl<K, V> Root<K, V> {
pub fn is_shared_root(&self) -> bool {
self.as_ref().is_shared_root()
}
pub fn shared_empty_root() -> Self {
Root {
node: unsafe {
BoxedNode::from_ptr(NonNull::new_unchecked(
&EMPTY_ROOT_NODE as *const _ as *const LeafNode<K, V> as *mut _,
))
},
height: 0,
}
}
pub fn new_leaf() -> Result<Self, TryReserveError> {
Ok(Root {
node: BoxedNode::from_leaf(<Box<_> as FallibleBox<_>>::try_new(unsafe {
LeafNode::new()
})?),
height: 0,
})
}
pub fn as_ref(&self) -> NodeRef<marker::Immut<'_>, K, V, marker::LeafOrInternal> {
NodeRef {
height: self.height,
node: self.node.as_ptr(),
root: self as *const _ as *mut _,
_marker: PhantomData,
}
}
pub fn as_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::LeafOrInternal> {
NodeRef {
height: self.height,
node: self.node.as_ptr(),
root: self as *mut _,
_marker: PhantomData,
}
}
pub fn into_ref(self) -> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
NodeRef {
height: self.height,
node: self.node.as_ptr(),
root: ptr::null_mut(), // FIXME: Is there anything better to do here?
_marker: PhantomData,
}
}
/// Adds a new internal node with a single edge, pointing to the previous root, and make that
/// new node the root. This increases the height by 1 and is the opposite of `pop_level`.
pub fn push_level(
&mut self,
) -> Result<NodeRef<marker::Mut<'_>, K, V, marker::Internal>, TryReserveError> {
debug_assert!(!self.is_shared_root());
let mut new_node = <Box<_> as FallibleBox<_>>::try_new(unsafe { InternalNode::new() })?;
new_node.edges[0].write(unsafe { BoxedNode::from_ptr(self.node.as_ptr()) });
self.node = BoxedNode::from_internal(new_node);
self.height += 1;
let mut ret = NodeRef {
height: self.height,
node: self.node.as_ptr(),
root: self as *mut _,
_marker: PhantomData,
};
unsafe {
ret.reborrow_mut().first_edge().correct_parent_link();
}
Ok(ret)
}
/// Removes the root node, using its first child as the new root. This cannot be called when
/// the tree consists only of a leaf node. As it is intended only to be called when the root
/// has only one edge, no cleanup is done on any of the other children are elements of the root.
/// This decreases the height by 1 and is the opposite of `push_level`.
pub fn pop_level(&mut self) {
debug_assert!(self.height > 0);
let top = self.node.ptr;
self.node = unsafe {
BoxedNode::from_ptr(
self.as_mut()
.cast_unchecked::<marker::Internal>()
.first_edge()
.descend()
.node,
)
};
self.height -= 1;
unsafe {
(*self.as_mut().as_leaf_mut()).parent = ptr::null();
}
unsafe {
Global.deallocate(
NonNull::from(top).cast(),
Layout::new::<InternalNode<K, V>>(),
);
}
}
}
// N.B. `NodeRef` is always covariant in `K` and `V`, even when the `BorrowType`
// is `Mut`. This is technically wrong, but cannot result in any unsafety due to
// internal use of `NodeRef` because we stay completely generic over `K` and `V`.
// However, whenever a public type wraps `NodeRef`, make sure that it has the
// correct variance.
/// A reference to a node.
///
/// This type has a number of parameters that controls how it acts:
/// - `BorrowType`: This can be `Immut<'a>` or `Mut<'a>` for some `'a` or `Owned`.
/// When this is `Immut<'a>`, the `NodeRef` acts roughly like `&'a Node`,
/// when this is `Mut<'a>`, the `NodeRef` acts roughly like `&'a mut Node`,
/// and when this is `Owned`, the `NodeRef` acts roughly like `Box<Node>`.
/// - `K` and `V`: These control what types of things are stored in the nodes.
/// - `Type`: This can be `Leaf`, `Internal`, or `LeafOrInternal`. When this is
/// `Leaf`, the `NodeRef` points to a leaf node, when this is `Internal` the
/// `NodeRef` points to an internal node, and when this is `LeafOrInternal` the
/// `NodeRef` could be pointing to either type of node.
/// Note that in case of a leaf node, this might still be the shared root! Only turn
/// this into a `LeafNode` reference if you know it is not a root! Shared references
/// must be dereferencable *for the entire size of their pointee*, so `&InternalNode`
/// pointing to the shared root is UB.
/// Turning this into a `NodeHeader` is always safe.
pub struct NodeRef<BorrowType, K, V, Type> {
height: usize,
node: NonNull<LeafNode<K, V>>,
// This is null unless the borrow type is `Mut`
root: *const Root<K, V>,
_marker: PhantomData<(BorrowType, Type)>,
}
impl<'a, K: 'a, V: 'a, Type> Copy for NodeRef<marker::Immut<'a>, K, V, Type> {}
impl<'a, K: 'a, V: 'a, Type> Clone for NodeRef<marker::Immut<'a>, K, V, Type> {
fn clone(&self) -> Self {
*self
}
}
unsafe impl<BorrowType, K: Sync, V: Sync, Type> Sync for NodeRef<BorrowType, K, V, Type> {}
unsafe impl<'a, K: Sync + 'a, V: Sync + 'a, Type> Send for NodeRef<marker::Immut<'a>, K, V, Type> {}
unsafe impl<'a, K: Send + 'a, V: Send + 'a, Type> Send for NodeRef<marker::Mut<'a>, K, V, Type> {}
unsafe impl<K: Send, V: Send, Type> Send for NodeRef<marker::Owned, K, V, Type> {}
impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
fn as_internal(&self) -> &InternalNode<K, V> {
unsafe { &*(self.node.as_ptr() as *mut InternalNode<K, V>) }
}
}
impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
fn as_internal_mut(&mut self) -> &mut InternalNode<K, V> {
unsafe { &mut *(self.node.as_ptr() as *mut InternalNode<K, V>) }
}
}
impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
/// Finds the length of the node. This is the number of keys or values. In an
/// internal node, the number of edges is `len() + 1`.
pub fn len(&self) -> usize {
self.as_header().len as usize
}
/// Returns the height of this node in the whole tree. Zero height denotes the
/// leaf level.
pub fn height(&self) -> usize {
self.height
}
/// Removes any static information about whether this node is a `Leaf` or an
/// `Internal` node.
pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
NodeRef {
height: self.height,
node: self.node,
root: self.root,
_marker: PhantomData,
}
}
/// Temporarily takes out another, immutable reference to the same node.
fn reborrow<'a>(&'a self) -> NodeRef<marker::Immut<'a>, K, V, Type> {
NodeRef {
height: self.height,
node: self.node,
root: self.root,
_marker: PhantomData,
}
}
/// Assert that this is indeed a proper leaf node, and not the shared root.
unsafe fn as_leaf(&self) -> &LeafNode<K, V> {
self.node.as_ref()
}
fn as_header(&self) -> &NodeHeader<K, V> {
unsafe { &*(self.node.as_ptr() as *const NodeHeader<K, V>) }
}
pub fn is_shared_root(&self) -> bool {
self.as_header().is_shared_root()
}
pub fn keys(&self) -> &[K] {
self.reborrow().into_key_slice()
}
fn vals(&self) -> &[V] {
self.reborrow().into_val_slice()
}
/// Finds the parent of the current node. Returns `Ok(handle)` if the current
/// node actually has a parent, where `handle` points to the edge of the parent
/// that points to the current node. Returns `Err(self)` if the current node has
/// no parent, giving back the original `NodeRef`.
///
/// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
/// both, upon success, do nothing.
pub fn ascend(
self,
) -> Result<Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge>, Self> {
let parent_as_leaf = self.as_header().parent as *const LeafNode<K, V>;
if let Some(non_zero) = NonNull::new(parent_as_leaf as *mut _) {
Ok(Handle {
node: NodeRef {
height: self.height + 1,
node: non_zero,
root: self.root,
_marker: PhantomData,
},
idx: unsafe { usize::from(*self.as_header().parent_idx.as_ptr()) },
_marker: PhantomData,
})
} else {
Err(self)
}
}
pub fn first_edge(self) -> Handle<Self, marker::Edge> {
Handle::new_edge(self, 0)
}
pub fn last_edge(self) -> Handle<Self, marker::Edge> {
let len = self.len();
Handle::new_edge(self, len)
}
/// Note that `self` must be nonempty.
pub fn first_kv(self) -> Handle<Self, marker::KV> {
debug_assert!(self.len() > 0);
Handle::new_kv(self, 0)
}
/// Note that `self` must be nonempty.
pub fn last_kv(self) -> Handle<Self, marker::KV> {
let len = self.len();
debug_assert!(len > 0);
Handle::new_kv(self, len - 1)
}
}
impl<K, V> NodeRef<marker::Owned, K, V, marker::Leaf> {
/// Similar to `ascend`, gets a reference to a node's parent node, but also
/// deallocate the current node in the process. This is unsafe because the
/// current node will still be accessible despite being deallocated.
pub unsafe fn deallocate_and_ascend(
self,
) -> Option<Handle<NodeRef<marker::Owned, K, V, marker::Internal>, marker::Edge>> {
debug_assert!(!self.is_shared_root());
let node = self.node;
let ret = self.ascend().ok();
Global.deallocate(node.cast(), Layout::new::<LeafNode<K, V>>());
ret
}
}
impl<K, V> NodeRef<marker::Owned, K, V, marker::Internal> {
/// Similar to `ascend`, gets a reference to a node's parent node, but also
/// deallocate the current node in the process. This is unsafe because the
/// current node will still be accessible despite being deallocated.
pub unsafe fn deallocate_and_ascend(
self,
) -> Option<Handle<NodeRef<marker::Owned, K, V, marker::Internal>, marker::Edge>> {
let node = self.node;
let ret = self.ascend().ok();
Global.deallocate(node.cast(), Layout::new::<InternalNode<K, V>>());
ret
}
}
impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
/// Unsafely asserts to the compiler some static information about whether this
/// node is a `Leaf`.
unsafe fn cast_unchecked<NewType>(&mut self) -> NodeRef<marker::Mut<'_>, K, V, NewType> {
NodeRef {
height: self.height,
node: self.node,
root: self.root,
_marker: PhantomData,
}
}
/// Temporarily takes out another, mutable reference to the same node. Beware, as
/// this method is very dangerous, doubly so since it may not immediately appear
/// dangerous.
///
/// Because mutable pointers can roam anywhere around the tree and can even (through
/// `into_root_mut`) mess with the root of the tree, the result of `reborrow_mut`
/// can easily be used to make the original mutable pointer dangling, or, in the case
/// of a reborrowed handle, out of bounds.
// FIXME(@gereeter) consider adding yet another type parameter to `NodeRef` that restricts
// the use of `ascend` and `into_root_mut` on reborrowed pointers, preventing this unsafety.
unsafe fn reborrow_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, Type> {
NodeRef {
height: self.height,
node: self.node,
root: self.root,
_marker: PhantomData,
}
}
/// Returns a raw ptr to avoid asserting exclusive access to the entire node.
fn as_leaf_mut(&mut self) -> *mut LeafNode<K, V> {
// We are mutable, so we cannot be the root, so accessing this as a leaf is okay.
self.node.as_ptr()
}
fn keys_mut(&mut self) -> &mut [K] {
unsafe { self.reborrow_mut().into_key_slice_mut() }
}
fn vals_mut(&mut self) -> &mut [V] {
unsafe { self.reborrow_mut().into_val_slice_mut() }
}
}
impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
fn into_key_slice(self) -> &'a [K] {
// We have to be careful here because we might be pointing to the shared root.
// In that case, we must not create an `&LeafNode`. We could just return
// an empty slice whenever the length is 0 (this includes the shared root),
// but we want to avoid that run-time check.
// Instead, we create a slice pointing into the node whenever possible.
// We can sometimes do this even for the shared root, as the slice will be
// empty. We cannot *always* do this because if the type is too highly
// aligned, the offset of `keys` in a "full node" might be outside the bounds
// of the header! So we do an alignment check first, that will be
// evaluated at compile-time, and only do any run-time check in the rare case
// that the alignment is very big.
if mem::align_of::<K>() > mem::align_of::<LeafNode<(), ()>>() && self.is_shared_root() {
&[]
} else {
// Thanks to the alignment check above, we know that `keys` will be
// in-bounds of some allocation even if this is the shared root!
// (We might be one-past-the-end, but that is allowed by LLVM.)
// Getting the pointer is tricky though. `NodeHeader` does not have a `keys`
// field because we want its size to not depend on the alignment of `K`
// (needed becuase `as_header` should be safe). We cannot call `as_leaf`
// because we might be the shared root.
// For this reason, `NodeHeader` has this `K2` parameter (that's usually `()`
// and hence just adds a size-0-align-1 field, not affecting layout).
// We know that we can transmute `NodeHeader<K, V, ()>` to `NodeHeader<K, V, K>`
// because we did the alignment check above, and hence `NodeHeader<K, V, K>`
// is not bigger than `NodeHeader<K, V, ()>`! Then we can use `NodeHeader<K, V, K>`
// to compute the pointer where the keys start.
// This entire hack will become unnecessary once
// <https://github.com/rust-lang/rfcs/pull/2582> lands, then we can just take a raw
// pointer to the `keys` field of `*const InternalNode<K, V>`.
// This is a non-debug-assert because it can be completely compile-time evaluated.
assert!(mem::size_of::<NodeHeader<K, V>>() == mem::size_of::<NodeHeader<K, V, K>>());
let header = self.as_header() as *const _ as *const NodeHeader<K, V, K>;
let keys = unsafe { &(*header).keys_start as *const _ as *const K };
unsafe { slice::from_raw_parts(keys, self.len()) }
}
}
fn into_val_slice(self) -> &'a [V] {
debug_assert!(!self.is_shared_root());
// We cannot be the root, so `as_leaf` is okay
unsafe {
slice::from_raw_parts(MaybeUninit::slice_as_ptr(&self.as_leaf().vals), self.len())
}
}
fn into_slices(self) -> (&'a [K], &'a [V]) {
let k = unsafe { ptr::read(&self) };
(k.into_key_slice(), self.into_val_slice())
}
}
impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
/// Gets a mutable reference to the root itself. This is useful primarily when the
/// height of the tree needs to be adjusted. Never call this on a reborrowed pointer.
pub fn into_root_mut(self) -> &'a mut Root<K, V> {
unsafe { &mut *(self.root as *mut Root<K, V>) }
}
fn into_key_slice_mut(mut self) -> &'a mut [K] {
// Same as for `into_key_slice` above, we try to avoid a run-time check
// (the alignment comparison will usually be performed at compile-time).
if mem::align_of::<K>() > mem::align_of::<LeafNode<(), ()>>() && self.is_shared_root() {
&mut []
} else {
unsafe {
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut (*self.as_leaf_mut()).keys),
self.len(),
)
}
}
}
fn into_val_slice_mut(mut self) -> &'a mut [V] {
debug_assert!(!self.is_shared_root());
unsafe {
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut (*self.as_leaf_mut()).vals),
self.len(),
)
}
}
fn into_slices_mut(mut self) -> (&'a mut [K], &'a mut [V]) {
debug_assert!(!self.is_shared_root());
// We cannot use the getters here, because calling the second one
// invalidates the reference returned by the first.
// More precisely, it is the call to `len` that is the culprit,
// because that creates a shared reference to the header, which *can*
// overlap with the keys (and even the values, for ZST keys).
unsafe {
let len = self.len();
let leaf = self.as_leaf_mut();
let keys =
slice::from_raw_parts_mut(MaybeUninit::slice_as_mut_ptr(&mut (*leaf).keys), len);
let vals =
slice::from_raw_parts_mut(MaybeUninit::slice_as_mut_ptr(&mut (*leaf).vals), len);
(keys, vals)
}
}
}
impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
/// Adds a key/value pair the end of the node.
pub fn push(&mut self, key: K, val: V) {
// Necessary for correctness, but this is an internal module
debug_assert!(self.len() < CAPACITY);
debug_assert!(!self.is_shared_root());
let idx = self.len();
unsafe {
ptr::write(self.keys_mut().as_mut_ptr().add(idx), key);
ptr::write(self.vals_mut().as_mut_ptr().add(idx), val);
(*self.as_leaf_mut()).len += 1;
}
}
/// Adds a key/value pair to the beginning of the node.
pub fn push_front(&mut self, key: K, val: V) {
// Necessary for correctness, but this is an internal module
debug_assert!(self.len() < CAPACITY);
debug_assert!(!self.is_shared_root());
unsafe {
slice_insert(self.keys_mut(), 0, key);
slice_insert(self.vals_mut(), 0, val);
(*self.as_leaf_mut()).len += 1;
}
}
}
impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
/// Adds a key/value pair and an edge to go to the right of that pair to
/// the end of the node.
pub fn push(&mut self, key: K, val: V, edge: Root<K, V>) {
// Necessary for correctness, but this is an internal module
debug_assert!(edge.height == self.height - 1);
debug_assert!(self.len() < CAPACITY);
let idx = self.len();
unsafe {
ptr::write(self.keys_mut().as_mut_ptr().add(idx), key);
ptr::write(self.vals_mut().as_mut_ptr().add(idx), val);
self.as_internal_mut()
.edges
.as_mut_ptr()
.add(idx + 1)
.as_mut()
.unwrap()
.write(edge.node);
(*self.as_leaf_mut()).len += 1;
Handle::new_edge(self.reborrow_mut(), idx + 1).correct_parent_link();
}
}
fn correct_childrens_parent_links(&mut self, first: usize, after_last: usize) {
for i in first..after_last {
Handle::new_edge(unsafe { self.reborrow_mut() }, i).correct_parent_link();
}
}
fn correct_all_childrens_parent_links(&mut self) {
let len = self.len();
self.correct_childrens_parent_links(0, len + 1);
}
/// Adds a key/value pair and an edge to go to the left of that pair to
/// the beginning of the node.
pub fn push_front(&mut self, key: K, val: V, edge: Root<K, V>) {
// Necessary for correctness, but this is an internal module
debug_assert!(edge.height == self.height - 1);
debug_assert!(self.len() < CAPACITY);
unsafe {
slice_insert(self.keys_mut(), 0, key);
slice_insert(self.vals_mut(), 0, val);
slice_insert(
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut self.as_internal_mut().edges),
self.len() + 1,
),
0,
edge.node,
);
(*self.as_leaf_mut()).len += 1;
self.correct_all_childrens_parent_links();
}
}
}
impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
/// Removes a key/value pair from the end of this node. If this is an internal node,
/// also removes the edge that was to the right of that pair.
pub fn pop(&mut self) -> (K, V, Option<Root<K, V>>) {
// Necessary for correctness, but this is an internal module
debug_assert!(self.len() > 0);
let idx = self.len() - 1;
unsafe {
let key = ptr::read(self.keys().get_unchecked(idx));
let val = ptr::read(self.vals().get_unchecked(idx));
let edge = match self.reborrow_mut().force() {
ForceResult::Leaf(_) => None,
ForceResult::Internal(internal) => {
let edge =
ptr::read(internal.as_internal().edges.get_unchecked(idx + 1).as_ptr());
let mut new_root = Root {
node: edge,
height: internal.height - 1,
};
(*new_root.as_mut().as_leaf_mut()).parent = ptr::null();
Some(new_root)
}
};
(*self.as_leaf_mut()).len -= 1;
(key, val, edge)
}
}
/// Removes a key/value pair from the beginning of this node. If this is an internal node,
/// also removes the edge that was to the left of that pair.
pub fn pop_front(&mut self) -> (K, V, Option<Root<K, V>>) {
// Necessary for correctness, but this is an internal module
debug_assert!(self.len() > 0);
let old_len = self.len();
unsafe {
let key = slice_remove(self.keys_mut(), 0);
let val = slice_remove(self.vals_mut(), 0);
let edge = match self.reborrow_mut().force() {
ForceResult::Leaf(_) => None,
ForceResult::Internal(mut internal) => {
let edge = slice_remove(
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut internal.as_internal_mut().edges),
old_len + 1,
),
0,
);
let mut new_root = Root {
node: edge,
height: internal.height - 1,
};
(*new_root.as_mut().as_leaf_mut()).parent = ptr::null();
for i in 0..old_len {
Handle::new_edge(internal.reborrow_mut(), i).correct_parent_link();
}
Some(new_root)
}
};
(*self.as_leaf_mut()).len -= 1;
(key, val, edge)
}
}
fn into_kv_pointers_mut(mut self) -> (*mut K, *mut V) {
(self.keys_mut().as_mut_ptr(), self.vals_mut().as_mut_ptr())
}
}
impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
/// Checks whether a node is an `Internal` node or a `Leaf` node.
pub fn force(
self,
) -> ForceResult<
NodeRef<BorrowType, K, V, marker::Leaf>,
NodeRef<BorrowType, K, V, marker::Internal>,
> {
if self.height == 0 {
ForceResult::Leaf(NodeRef {
height: self.height,
node: self.node,
root: self.root,
_marker: PhantomData,
})
} else {
ForceResult::Internal(NodeRef {
height: self.height,
node: self.node,
root: self.root,
_marker: PhantomData,
})
}
}
}
/// A reference to a specific key/value pair or edge within a node. The `Node` parameter
/// must be a `NodeRef`, while the `Type` can either be `KV` (signifying a handle on a key/value
/// pair) or `Edge` (signifying a handle on an edge).
///
/// Note that even `Leaf` nodes can have `Edge` handles. Instead of representing a pointer to
/// a child node, these represent the spaces where child pointers would go between the key/value
/// pairs. For example, in a node with length 2, there would be 3 possible edge locations - one
/// to the left of the node, one between the two pairs, and one at the right of the node.
pub struct Handle<Node, Type> {
node: Node,
idx: usize,
_marker: PhantomData<Type>,
}
impl<Node: Copy, Type> Copy for Handle<Node, Type> {}
// We don't need the full generality of `#[derive(Clone)]`, as the only time `Node` will be
// `Clone`able is when it is an immutable reference and therefore `Copy`.
impl<Node: Copy, Type> Clone for Handle<Node, Type> {
fn clone(&self) -> Self {
*self
}
}
impl<Node, Type> Handle<Node, Type> {
/// Retrieves the node that contains the edge of key/value pair this handle points to.
pub fn into_node(self) -> Node {
self.node
}
}
impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV> {
/// Creates a new handle to a key/value pair in `node`. `idx` must be less than `node.len()`.
pub fn new_kv(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
// Necessary for correctness, but in a private module
debug_assert!(idx < node.len());
Handle {
node,
idx,
_marker: PhantomData,
}
}
pub fn left_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
Handle::new_edge(self.node, self.idx)
}
pub fn right_edge(self) -> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
Handle::new_edge(self.node, self.idx + 1)
}
}
impl<BorrowType, K, V, NodeType, HandleType> PartialEq
for Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
{
fn eq(&self, other: &Self) -> bool {
self.node.node == other.node.node && self.idx == other.idx
}
}
impl<BorrowType, K, V, NodeType, HandleType>
Handle<NodeRef<BorrowType, K, V, NodeType>, HandleType>
{
/// Temporarily takes out another, immutable handle on the same location.
pub fn reborrow(&self) -> Handle<NodeRef<marker::Immut<'_>, K, V, NodeType>, HandleType> {
// We can't use Handle::new_kv or Handle::new_edge because we don't know our type
Handle {
node: self.node.reborrow(),
idx: self.idx,
_marker: PhantomData,
}
}
}
impl<'a, K, V, NodeType, HandleType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
/// Temporarily takes out another, mutable handle on the same location. Beware, as
/// this method is very dangerous, doubly so since it may not immediately appear
/// dangerous.
///
/// Because mutable pointers can roam anywhere around the tree and can even (through
/// `into_root_mut`) mess with the root of the tree, the result of `reborrow_mut`
/// can easily be used to make the original mutable pointer dangling, or, in the case
/// of a reborrowed handle, out of bounds.
// FIXME(@gereeter) consider adding yet another type parameter to `NodeRef` that restricts
// the use of `ascend` and `into_root_mut` on reborrowed pointers, preventing this unsafety.
pub unsafe fn reborrow_mut(
&mut self,
) -> Handle<NodeRef<marker::Mut<'_>, K, V, NodeType>, HandleType> {
// We can't use Handle::new_kv or Handle::new_edge because we don't know our type
Handle {
node: self.node.reborrow_mut(),
idx: self.idx,
_marker: PhantomData,
}
}
}
impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
/// Creates a new handle to an edge in `node`. `idx` must be less than or equal to
/// `node.len()`.
pub fn new_edge(node: NodeRef<BorrowType, K, V, NodeType>, idx: usize) -> Self {
// Necessary for correctness, but in a private module
debug_assert!(idx <= node.len());
Handle {
node,
idx,
_marker: PhantomData,
}
}
pub fn left_kv(self) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
if self.idx > 0 {
Ok(Handle::new_kv(self.node, self.idx - 1))
} else {
Err(self)
}
}
pub fn right_kv(self) -> Result<Handle<NodeRef<BorrowType, K, V, NodeType>, marker::KV>, Self> {
if self.idx < self.node.len() {
Ok(Handle::new_kv(self.node, self.idx))
} else {
Err(self)
}
}
}
impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
/// Inserts a new key/value pair between the key/value pairs to the right and left of
/// this edge. This method assumes that there is enough space in the node for the new
/// pair to fit.
///
/// The returned pointer points to the inserted value.
fn insert_fit(&mut self, key: K, val: V) -> *mut V {
// Necessary for correctness, but in a private module
debug_assert!(self.node.len() < CAPACITY);
debug_assert!(!self.node.is_shared_root());
unsafe {
slice_insert(self.node.keys_mut(), self.idx, key);
slice_insert(self.node.vals_mut(), self.idx, val);
(*self.node.as_leaf_mut()).len += 1;
self.node.vals_mut().as_mut_ptr().add(self.idx)
}
}
/// Inserts a new key/value pair between the key/value pairs to the right and left of
/// this edge. This method splits the node if there isn't enough room.
///
/// The returned pointer points to the inserted value.
pub fn insert(
mut self,
key: K,
val: V,
) -> Result<(InsertResult<'a, K, V, marker::Leaf>, *mut V), TryReserveError> {
if self.node.len() < CAPACITY {
let ptr = self.insert_fit(key, val);
Ok((InsertResult::Fit(Handle::new_kv(self.node, self.idx)), ptr))
} else {
let middle = Handle::new_kv(self.node, B);
let (mut left, k, v, mut right) = middle.split()?;
let ptr = if self.idx <= B {
unsafe { Handle::new_edge(left.reborrow_mut(), self.idx).insert_fit(key, val) }
} else {
unsafe {
Handle::new_edge(
right.as_mut().cast_unchecked::<marker::Leaf>(),
self.idx - (B + 1),
)
.insert_fit(key, val)
}
};
Ok((InsertResult::Split(left, k, v, right), ptr))
}
}
}
impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
/// Fixes the parent pointer and index in the child node below this edge. This is useful
/// when the ordering of edges has been changed, such as in the various `insert` methods.
fn correct_parent_link(mut self) {
let idx = self.idx as u16;
let ptr = self.node.as_internal_mut() as *mut _;
let mut child = self.descend();
unsafe {
(*child.as_leaf_mut()).parent = ptr;
(*child.as_leaf_mut()).parent_idx.write(idx);
}
}
/// Unsafely asserts to the compiler some static information about whether the underlying
/// node of this handle is a `Leaf`.
unsafe fn cast_unchecked<NewType>(
&mut self,
) -> Handle<NodeRef<marker::Mut<'_>, K, V, NewType>, marker::Edge> {
Handle::new_edge(self.node.cast_unchecked(), self.idx)
}
/// Inserts a new key/value pair and an edge that will go to the right of that new pair
/// between this edge and the key/value pair to the right of this edge. This method assumes
/// that there is enough space in the node for the new pair to fit.
fn insert_fit(&mut self, key: K, val: V, edge: Root<K, V>) {
// Necessary for correctness, but in an internal module
debug_assert!(self.node.len() < CAPACITY);
debug_assert!(edge.height == self.node.height - 1);
unsafe {
// This cast is a lie, but it allows us to reuse the key/value insertion logic.
self.cast_unchecked::<marker::Leaf>().insert_fit(key, val);
slice_insert(
slice::from_raw_parts_mut(
MaybeUninit::slice_as_mut_ptr(&mut self.node.as_internal_mut().edges),
self.node.len(),
),
self.idx + 1,
edge.node,
);
for i in (self.idx + 1)..(self.node.len() + 1) {
Handle::new_edge(self.node.reborrow_mut(), i).correct_parent_link();
}
}
}
/// Inserts a new key/value pair and an edge that will go to the right of that new pair
/// between this edge and the key/value pair to the right of this edge. This method splits
/// the node if there isn't enough room.
pub fn insert(
mut self,
key: K,
val: V,
edge: Root<K, V>,
) -> Result<InsertResult<'a, K, V, marker::Internal>, TryReserveError> {
// Necessary for correctness, but this is an internal module
debug_assert!(edge.height == self.node.height - 1);
if self.node.len() < CAPACITY {
self.insert_fit(key, val, edge);
Ok(InsertResult::Fit(Handle::new_kv(self.node, self.idx)))
} else {
let middle = Handle::new_kv(self.node, B);
let (mut left, k, v, mut right) = middle.split()?;
if self.idx <= B {
unsafe {
Handle::new_edge(left.reborrow_mut(), self.idx).insert_fit(key, val, edge);
}
} else {
unsafe {
Handle::new_edge(
right.as_mut().cast_unchecked::<marker::Internal>(),
self.idx - (B + 1),
)
.insert_fit(key, val, edge);
}
}
Ok(InsertResult::Split(left, k, v, right))
}
}
}
impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge> {
/// Finds the node pointed to by this edge.
///
/// `edge.descend().ascend().unwrap()` and `node.ascend().unwrap().descend()` should
/// both, upon success, do nothing.
pub fn descend(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
NodeRef {
height: self.node.height - 1,
node: unsafe {
(&*self
.node
.as_internal()
.edges
.get_unchecked(self.idx)
.as_ptr())
.as_ptr()
},
root: self.node.root,
_marker: PhantomData,
}
}
}
impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Immut<'a>, K, V, NodeType>, marker::KV> {
pub fn into_kv(self) -> (&'a K, &'a V) {
let (keys, vals) = self.node.into_slices();
unsafe { (keys.get_unchecked(self.idx), vals.get_unchecked(self.idx)) }
}
}
impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
pub fn into_kv_mut(self) -> (&'a mut K, &'a mut V) {
let (keys, vals) = self.node.into_slices_mut();
unsafe {
(
keys.as_mut_ptr().add(self.idx).as_mut().unwrap(),
vals.as_mut_ptr().add(self.idx).as_mut().unwrap(),
)
}
}
}
impl<'a, K, V, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
pub fn kv_mut(&mut self) -> (&mut K, &mut V) {
unsafe {
let (keys, vals) = self.node.reborrow_mut().into_slices_mut();
(
keys.as_mut_ptr().add(self.idx).as_mut().unwrap(),
vals.as_mut_ptr().add(self.idx).as_mut().unwrap(),
)
}
}
}
impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
/// Splits the underlying node into three parts:
///
/// - The node is truncated to only contain the key/value pairs to the right of
/// this handle.
/// - The key and value pointed to by this handle and extracted.
/// - All the key/value pairs to the right of this handle are put into a newly
/// allocated node.
pub fn split(
mut self,
) -> Result<
(
NodeRef<marker::Mut<'a>, K, V, marker::Leaf>,
K,
V,
Root<K, V>,
),
TryReserveError,
> {
debug_assert!(!self.node.is_shared_root());
unsafe {
let mut new_node = <Box<_> as FallibleBox<_>>::try_new(LeafNode::new())?;
let k = ptr::read(self.node.keys().get_unchecked(self.idx));
let v = ptr::read(self.node.vals().get_unchecked(self.idx));
let new_len = self.node.len() - self.idx - 1;
ptr::copy_nonoverlapping(
self.node.keys().as_ptr().add(self.idx + 1),
new_node.keys.as_mut_ptr() as *mut K,
new_len,
);
ptr::copy_nonoverlapping(
self.node.vals().as_ptr().add(self.idx + 1),
new_node.vals.as_mut_ptr() as *mut V,
new_len,
);
(*self.node.as_leaf_mut()).len = self.idx as u16;
new_node.len = new_len as u16;
Ok((
self.node,
k,
v,
Root {
node: BoxedNode::from_leaf(new_node),
height: 0,
},
))
}
}
/// Removes the key/value pair pointed to by this handle, returning the edge between the
/// now adjacent key/value pairs to the left and right of this handle.
pub fn remove(
mut self,
) -> (
Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>,
K,
V,
) {
debug_assert!(!self.node.is_shared_root());
unsafe {
let k = slice_remove(self.node.keys_mut(), self.idx);
let v = slice_remove(self.node.vals_mut(), self.idx);
(*self.node.as_leaf_mut()).len -= 1;
(self.left_edge(), k, v)
}
}
}
impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::KV> {
/// Splits the underlying node into three parts:
///
/// - The node is truncated to only contain the edges and key/value pairs to the
/// right of this handle.
/// - The key and value pointed to by this handle and extracted.
/// - All the edges and key/value pairs to the right of this handle are put into
/// a newly allocated node.
pub fn split(
mut self,
) -> Result<
(
NodeRef<marker::Mut<'a>, K, V, marker::Internal>,
K,
V,
Root<K, V>,
),
TryReserveError,
> {
unsafe {
let mut new_node = <Box<_> as FallibleBox<_>>::try_new(InternalNode::new())?;
let k = ptr::read(self.node.keys().get_unchecked(self.idx));
let v = ptr::read(self.node.vals().get_unchecked(self.idx));
let height = self.node.height;
let new_len = self.node.len() - self.idx - 1;
ptr::copy_nonoverlapping(
self.node.keys().as_ptr().add(self.idx + 1),
new_node.data.keys.as_mut_ptr() as *mut K,
new_len,
);
ptr::copy_nonoverlapping(
self.node.vals().as_ptr().add(self.idx + 1),
new_node.data.vals.as_mut_ptr() as *mut V,
new_len,
);
ptr::copy_nonoverlapping(
self.node.as_internal().edges.as_ptr().add(self.idx + 1),
new_node.edges.as_mut_ptr(),
new_len + 1,
);
(*self.node.as_leaf_mut()).len = self.idx as u16;
new_node.data.len = new_len as u16;
let mut new_root = Root {
node: BoxedNode::from_internal(new_node),
height,
};
for i in 0..(new_len + 1) {
Handle::new_edge(new_root.as_mut().cast_unchecked(), i).correct_parent_link();
}
Ok((self.node, k, v, new_root))
}
}
/// Returns `true` if it is valid to call `.merge()`, i.e., whether there is enough room in
/// a node to hold the combination of the nodes to the left and right of this handle along
/// with the key/value pair at this handle.
pub fn can_merge(&self) -> bool {
(self.reborrow().left_edge().descend().len()
+ self.reborrow().right_edge().descend().len()
+ 1)
<= CAPACITY
}
/// Combines the node immediately to the left of this handle, the key/value pair pointed
/// to by this handle, and the node immediately to the right of this handle into one new
/// child of the underlying node, returning an edge referencing that new child.
///
/// Assumes that this edge `.can_merge()`.
pub fn merge(
mut self,
) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
let self1 = unsafe { ptr::read(&self) };
let self2 = unsafe { ptr::read(&self) };
let mut left_node = self1.left_edge().descend();
let left_len = left_node.len();
let mut right_node = self2.right_edge().descend();
let right_len = right_node.len();
// necessary for correctness, but in a private module
debug_assert!(left_len + right_len + 1 <= CAPACITY);
unsafe {
ptr::write(
left_node.keys_mut().as_mut_ptr().add(left_len),
slice_remove(self.node.keys_mut(), self.idx),
);
ptr::copy_nonoverlapping(
right_node.keys().as_ptr(),
left_node.keys_mut().as_mut_ptr().add(left_len + 1),
right_len,
);
ptr::write(
left_node.vals_mut().as_mut_ptr().add(left_len),
slice_remove(self.node.vals_mut(), self.idx),
);
ptr::copy_nonoverlapping(
right_node.vals().as_ptr(),
left_node.vals_mut().as_mut_ptr().add(left_len + 1),
right_len,
);
slice_remove(&mut self.node.as_internal_mut().edges, self.idx + 1);
for i in self.idx + 1..self.node.len() {
Handle::new_edge(self.node.reborrow_mut(), i).correct_parent_link();
}
(*self.node.as_leaf_mut()).len -= 1;
(*left_node.as_leaf_mut()).len += right_len as u16 + 1;
if self.node.height > 1 {
ptr::copy_nonoverlapping(
right_node.cast_unchecked().as_internal().edges.as_ptr(),
left_node
.cast_unchecked()
.as_internal_mut()
.edges
.as_mut_ptr()
.add(left_len + 1),
right_len + 1,
);
for i in left_len + 1..left_len + right_len + 2 {
Handle::new_edge(left_node.cast_unchecked().reborrow_mut(), i)
.correct_parent_link();
}
Global.deallocate(right_node.node.cast(), Layout::new::<InternalNode<K, V>>());
} else {
Global.deallocate(right_node.node.cast(), Layout::new::<LeafNode<K, V>>());
}
Handle::new_edge(self.node, self.idx)
}
}
/// This removes a key/value pair from the left child and replaces it with the key/value pair
/// pointed to by this handle while pushing the old key/value pair of this handle into the right
/// child.
pub fn steal_left(&mut self) {
unsafe {
let (k, v, edge) = self.reborrow_mut().left_edge().descend().pop();
let k = mem::replace(self.reborrow_mut().into_kv_mut().0, k);
let v = mem::replace(self.reborrow_mut().into_kv_mut().1, v);
match self.reborrow_mut().right_edge().descend().force() {
ForceResult::Leaf(mut leaf) => leaf.push_front(k, v),
ForceResult::Internal(mut internal) => internal.push_front(k, v, edge.unwrap()),
}
}
}
/// This removes a key/value pair from the right child and replaces it with the key/value pair
/// pointed to by this handle while pushing the old key/value pair of this handle into the left
/// child.
pub fn steal_right(&mut self) {
unsafe {
let (k, v, edge) = self.reborrow_mut().right_edge().descend().pop_front();
let k = mem::replace(self.reborrow_mut().into_kv_mut().0, k);
let v = mem::replace(self.reborrow_mut().into_kv_mut().1, v);
match self.reborrow_mut().left_edge().descend().force() {
ForceResult::Leaf(mut leaf) => leaf.push(k, v),
ForceResult::Internal(mut internal) => internal.push(k, v, edge.unwrap()),
}
}
}
/// This does stealing similar to `steal_left` but steals multiple elements at once.
pub fn bulk_steal_left(&mut self, count: usize) {
unsafe {
let mut left_node = ptr::read(self).left_edge().descend();
let left_len = left_node.len();
let mut right_node = ptr::read(self).right_edge().descend();
let right_len = right_node.len();
// Make sure that we may steal safely.
debug_assert!(right_len + count <= CAPACITY);
debug_assert!(left_len >= count);
let new_left_len = left_len - count;
// Move data.
{
let left_kv = left_node.reborrow_mut().into_kv_pointers_mut();
let right_kv = right_node.reborrow_mut().into_kv_pointers_mut();
let parent_kv = {
let kv = self.reborrow_mut().into_kv_mut();
(kv.0 as *mut K, kv.1 as *mut V)
};
// Make room for stolen elements in the right child.
ptr::copy(right_kv.0, right_kv.0.add(count), right_len);
ptr::copy(right_kv.1, right_kv.1.add(count), right_len);
// Move elements from the left child to the right one.
move_kv(left_kv, new_left_len + 1, right_kv, 0, count - 1);
// Move parent's key/value pair to the right child.
move_kv(parent_kv, 0, right_kv, count - 1, 1);
// Move the left-most stolen pair to the parent.
move_kv(left_kv, new_left_len, parent_kv, 0, 1);
}
(*left_node.reborrow_mut().as_leaf_mut()).len -= count as u16;
(*right_node.reborrow_mut().as_leaf_mut()).len += count as u16;
match (left_node.force(), right_node.force()) {
(ForceResult::Internal(left), ForceResult::Internal(mut right)) => {
// Make room for stolen edges.
let right_edges = right.reborrow_mut().as_internal_mut().edges.as_mut_ptr();
ptr::copy(right_edges, right_edges.add(count), right_len + 1);
right.correct_childrens_parent_links(count, count + right_len + 1);
move_edges(left, new_left_len + 1, right, 0, count);
}
(ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
_ => {
unreachable!();
}
}
}
}
/// The symmetric clone of `bulk_steal_left`.
pub fn bulk_steal_right(&mut self, count: usize) {
unsafe {
let mut left_node = ptr::read(self).left_edge().descend();
let left_len = left_node.len();
let mut right_node = ptr::read(self).right_edge().descend();
let right_len = right_node.len();
// Make sure that we may steal safely.
debug_assert!(left_len + count <= CAPACITY);
debug_assert!(right_len >= count);
let new_right_len = right_len - count;
// Move data.
{
let left_kv = left_node.reborrow_mut().into_kv_pointers_mut();
let right_kv = right_node.reborrow_mut().into_kv_pointers_mut();
let parent_kv = {
let kv = self.reborrow_mut().into_kv_mut();
(kv.0 as *mut K, kv.1 as *mut V)
};
// Move parent's key/value pair to the left child.
move_kv(parent_kv, 0, left_kv, left_len, 1);
// Move elements from the right child to the left one.
move_kv(right_kv, 0, left_kv, left_len + 1, count - 1);
// Move the right-most stolen pair to the parent.
move_kv(right_kv, count - 1, parent_kv, 0, 1);
// Fix right indexing
ptr::copy(right_kv.0.add(count), right_kv.0, new_right_len);
ptr::copy(right_kv.1.add(count), right_kv.1, new_right_len);
}
(*left_node.reborrow_mut().as_leaf_mut()).len += count as u16;
(*right_node.reborrow_mut().as_leaf_mut()).len -= count as u16;
match (left_node.force(), right_node.force()) {
(ForceResult::Internal(left), ForceResult::Internal(mut right)) => {
move_edges(right.reborrow_mut(), 0, left, left_len + 1, count);
// Fix right indexing.
let right_edges = right.reborrow_mut().as_internal_mut().edges.as_mut_ptr();
ptr::copy(right_edges.add(count), right_edges, new_right_len + 1);
right.correct_childrens_parent_links(0, new_right_len + 1);
}
(ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
_ => {
unreachable!();
}
}
}
}
}
unsafe fn move_kv<K, V>(
source: (*mut K, *mut V),
source_offset: usize,
dest: (*mut K, *mut V),
dest_offset: usize,
count: usize,
) {
ptr::copy_nonoverlapping(source.0.add(source_offset), dest.0.add(dest_offset), count);
ptr::copy_nonoverlapping(source.1.add(source_offset), dest.1.add(dest_offset), count);
}
// Source and destination must have the same height.
unsafe fn move_edges<K, V>(
mut source: NodeRef<marker::Mut<'_>, K, V, marker::Internal>,
source_offset: usize,
mut dest: NodeRef<marker::Mut<'_>, K, V, marker::Internal>,
dest_offset: usize,
count: usize,
) {
let source_ptr = source.as_internal_mut().edges.as_mut_ptr();
let dest_ptr = dest.as_internal_mut().edges.as_mut_ptr();
ptr::copy_nonoverlapping(
source_ptr.add(source_offset),
dest_ptr.add(dest_offset),
count,
);
dest.correct_childrens_parent_links(dest_offset, dest_offset + count);
}
impl<BorrowType, K, V, HandleType>
Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, HandleType>
{
/// Checks whether the underlying node is an `Internal` node or a `Leaf` node.
pub fn force(
self,
) -> ForceResult<
Handle<NodeRef<BorrowType, K, V, marker::Leaf>, HandleType>,
Handle<NodeRef<BorrowType, K, V, marker::Internal>, HandleType>,
> {
match self.node.force() {
ForceResult::Leaf(node) => ForceResult::Leaf(Handle {
node,
idx: self.idx,
_marker: PhantomData,
}),
ForceResult::Internal(node) => ForceResult::Internal(Handle {
node,
idx: self.idx,
_marker: PhantomData,
}),
}
}
}
impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
/// Move the suffix after `self` from one node to another one. `right` must be empty.
/// The first edge of `right` remains unchanged.
pub fn move_suffix(
&mut self,
right: &mut NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
) {
unsafe {
let left_new_len = self.idx;
let mut left_node = self.reborrow_mut().into_node();
let right_new_len = left_node.len() - left_new_len;
let mut right_node = right.reborrow_mut();
debug_assert!(right_node.len() == 0);
debug_assert!(left_node.height == right_node.height);
let left_kv = left_node.reborrow_mut().into_kv_pointers_mut();
let right_kv = right_node.reborrow_mut().into_kv_pointers_mut();
move_kv(left_kv, left_new_len, right_kv, 0, right_new_len);
(*left_node.reborrow_mut().as_leaf_mut()).len = left_new_len as u16;
(*right_node.reborrow_mut().as_leaf_mut()).len = right_new_len as u16;
match (left_node.force(), right_node.force()) {
(ForceResult::Internal(left), ForceResult::Internal(right)) => {
move_edges(left, left_new_len + 1, right, 1, right_new_len);
}
(ForceResult::Leaf(_), ForceResult::Leaf(_)) => {}
_ => {
unreachable!();
}
}
}
}
}
pub enum ForceResult<Leaf, Internal> {
Leaf(Leaf),
Internal(Internal),
}
pub enum InsertResult<'a, K, V, Type> {
Fit(Handle<NodeRef<marker::Mut<'a>, K, V, Type>, marker::KV>),
Split(NodeRef<marker::Mut<'a>, K, V, Type>, K, V, Root<K, V>),
}
pub mod marker {
use core::marker::PhantomData;
pub enum Leaf {}
pub enum Internal {}
pub enum LeafOrInternal {}
pub enum Owned {}
pub struct Immut<'a>(PhantomData<&'a ()>);
pub struct Mut<'a>(PhantomData<&'a mut ()>);
pub enum KV {}
pub enum Edge {}
}
unsafe fn slice_insert<T>(slice: &mut [T], idx: usize, val: T) {
ptr::copy(
slice.as_ptr().add(idx),
slice.as_mut_ptr().add(idx + 1),
slice.len() - idx,
);
ptr::write(slice.as_mut_ptr().add(idx), val);
}
unsafe fn slice_remove<T>(slice: &mut [T], idx: usize) -> T {
let ret = ptr::read(slice.get_unchecked(idx));
ptr::copy(
slice.as_ptr().add(idx + 1),
slice.as_mut_ptr().add(idx),
slice.len() - idx - 1,
);
ret
}
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]
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2026-04-04
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