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node.rs
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node.rs
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// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
// This module represents all the internal representation and logic for a B-Tree's node
// with a safe interface, so that BTreeMap itself does not depend on any of these details.
pub use self::InsertionResult::*;
pub use self::SearchResult::*;
pub use self::ForceResult::*;
pub use self::TraversalItem::*;
use core::cmp::Ordering::{Greater, Less, Equal};
use core::intrinsics::arith_offset;
use core::iter::Zip;
use core::marker::PhantomData;
use core::ops::{Deref, DerefMut, Index, IndexMut};
use core::ptr::Unique;
use core::{slice, mem, ptr, cmp};
use alloc::heap;
use borrow::Borrow;
/// Represents the result of an Insertion: either the item fit, or the node had to split
pub enum InsertionResult<K, V> {
/// The inserted element fit
Fit,
/// The inserted element did not fit, so the node was split
Split(K, V, Node<K, V>),
}
/// Represents the result of a search for a key in a single node
pub enum SearchResult<NodeRef> {
/// The element was found at the given index
Found(Handle<NodeRef, handle::KV, handle::LeafOrInternal>),
/// The element wasn't found, but if it's anywhere, it must be beyond this edge
GoDown(Handle<NodeRef, handle::Edge, handle::LeafOrInternal>),
}
/// A B-Tree Node. We keep keys/edges/values separate to optimize searching for keys.
#[unsafe_no_drop_flag]
pub struct Node<K, V> {
// To avoid the need for multiple allocations, we allocate a single buffer with enough space
// for `capacity` keys, `capacity` values, and (in internal nodes) `capacity + 1` edges.
// Despite this, we store three separate pointers to the three "chunks" of the buffer because
// the performance drops significantly if the locations of the vals and edges need to be
// recalculated upon access.
//
// These will never be null during normal usage of a `Node`. However, to avoid the need for a
// drop flag, `Node::drop` zeroes `keys`, signaling that the `Node` has already been cleaned
// up.
keys: Unique<K>,
vals: Unique<V>,
// In leaf nodes, this will be None, and no space will be allocated for edges.
edges: Option<Unique<Node<K, V>>>,
// At any given time, there will be `_len` keys, `_len` values, and (in an internal node)
// `_len + 1` edges. In a leaf node, there will never be any edges.
//
// Note: instead of accessing this field directly, please call the `len()` method, which should
// be more stable in the face of representation changes.
_len: usize,
// FIXME(gereeter) It shouldn't be necessary to store the capacity in every node, as it should
// be constant throughout the tree. Once a solution to this is found, it might be possible to
// also pass down the offsets into the buffer that vals and edges are stored at, removing the
// need for those two pointers.
//
// Note: instead of accessing this field directly, please call the `capacity()` method, which
// should be more stable in the face of representation changes.
_capacity: usize,
}
pub struct NodeSlice<'a, K: 'a, V: 'a> {
keys: &'a [K],
vals: &'a [V],
pub edges: &'a [Node<K, V>],
head_is_edge: bool,
tail_is_edge: bool,
has_edges: bool,
}
pub struct MutNodeSlice<'a, K: 'a, V: 'a> {
keys: &'a [K],
vals: &'a mut [V],
pub edges: &'a mut [Node<K, V>],
head_is_edge: bool,
tail_is_edge: bool,
has_edges: bool,
}
/// Rounds up to a multiple of a power of two. Returns the closest multiple
/// of `target_alignment` that is higher or equal to `unrounded`.
///
/// # Panics
///
/// Fails if `target_alignment` is not a power of two.
#[inline]
fn round_up_to_next(unrounded: usize, target_alignment: usize) -> usize {
assert!(target_alignment.is_power_of_two());
(unrounded + target_alignment - 1) & !(target_alignment - 1)
}
#[test]
fn test_rounding() {
assert_eq!(round_up_to_next(0, 4), 0);
assert_eq!(round_up_to_next(1, 4), 4);
assert_eq!(round_up_to_next(2, 4), 4);
assert_eq!(round_up_to_next(3, 4), 4);
assert_eq!(round_up_to_next(4, 4), 4);
assert_eq!(round_up_to_next(5, 4), 8);
}
// Returns a tuple of (val_offset, edge_offset),
// from the start of a mallocated array.
#[inline]
fn calculate_offsets(keys_size: usize,
vals_size: usize,
vals_align: usize,
edges_align: usize)
-> (usize, usize) {
let vals_offset = round_up_to_next(keys_size, vals_align);
let end_of_vals = vals_offset + vals_size;
let edges_offset = round_up_to_next(end_of_vals, edges_align);
(vals_offset, edges_offset)
}
// Returns a tuple of (minimum required alignment, array_size),
// from the start of a mallocated array.
#[inline]
fn calculate_allocation(keys_size: usize,
keys_align: usize,
vals_size: usize,
vals_align: usize,
edges_size: usize,
edges_align: usize)
-> (usize, usize) {
let (_, edges_offset) = calculate_offsets(keys_size, vals_size, vals_align, edges_align);
let end_of_edges = edges_offset + edges_size;
let min_align = cmp::max(keys_align, cmp::max(vals_align, edges_align));
(min_align, end_of_edges)
}
#[test]
fn test_offset_calculation() {
assert_eq!(calculate_allocation(128, 8, 15, 1, 4, 4), (8, 148));
assert_eq!(calculate_allocation(3, 1, 2, 1, 1, 1), (1, 6));
assert_eq!(calculate_allocation(6, 2, 12, 4, 24, 8), (8, 48));
assert_eq!(calculate_offsets(128, 15, 1, 4), (128, 144));
assert_eq!(calculate_offsets(3, 2, 1, 1), (3, 5));
assert_eq!(calculate_offsets(6, 12, 4, 8), (8, 24));
}
fn calculate_allocation_generic<K, V>(capacity: usize, is_leaf: bool) -> (usize, usize) {
let (keys_size, keys_align) = (capacity * mem::size_of::<K>(), mem::align_of::<K>());
let (vals_size, vals_align) = (capacity * mem::size_of::<V>(), mem::align_of::<V>());
let (edges_size, edges_align) = if is_leaf {
// allocate one edge to ensure that we don't pass size 0 to `heap::allocate`
if mem::size_of::<K>() == 0 && mem::size_of::<V>() == 0 {
(1, mem::align_of::<Node<K, V>>())
} else {
(0, 1)
}
} else {
((capacity + 1) * mem::size_of::<Node<K, V>>(),
mem::align_of::<Node<K, V>>())
};
calculate_allocation(keys_size,
keys_align,
vals_size,
vals_align,
edges_size,
edges_align)
}
fn calculate_offsets_generic<K, V>(capacity: usize, is_leaf: bool) -> (usize, usize) {
let keys_size = capacity * mem::size_of::<K>();
let vals_size = capacity * mem::size_of::<V>();
let vals_align = mem::align_of::<V>();
let edges_align = if is_leaf {
1
} else {
mem::align_of::<Node<K, V>>()
};
calculate_offsets(keys_size, vals_size, vals_align, edges_align)
}
/// An iterator over a slice that owns the elements of the slice but not the allocation.
struct RawItems<T> {
head: *const T,
tail: *const T,
}
impl<T> RawItems<T> {
unsafe fn from_slice(slice: &[T]) -> RawItems<T> {
RawItems::from_parts(slice.as_ptr(), slice.len())
}
unsafe fn from_parts(ptr: *const T, len: usize) -> RawItems<T> {
if mem::size_of::<T>() == 0 {
RawItems {
head: ptr,
tail: arith_offset(ptr as *const i8, len as isize) as *const T,
}
} else {
RawItems {
head: ptr,
tail: ptr.offset(len as isize),
}
}
}
unsafe fn push(&mut self, val: T) {
ptr::write(self.tail as *mut T, val);
if mem::size_of::<T>() == 0 {
self.tail = arith_offset(self.tail as *const i8, 1) as *const T;
} else {
self.tail = self.tail.offset(1);
}
}
}
impl<T> Iterator for RawItems<T> {
type Item = T;
fn next(&mut self) -> Option<T> {
if self.head == self.tail {
None
} else {
unsafe {
let ret = Some(ptr::read(self.head));
if mem::size_of::<T>() == 0 {
self.head = arith_offset(self.head as *const i8, 1) as *const T;
} else {
self.head = self.head.offset(1);
}
ret
}
}
}
}
impl<T> DoubleEndedIterator for RawItems<T> {
fn next_back(&mut self) -> Option<T> {
if self.head == self.tail {
None
} else {
unsafe {
if mem::size_of::<T>() == 0 {
self.tail = arith_offset(self.tail as *const i8, -1) as *const T;
} else {
self.tail = self.tail.offset(-1);
}
Some(ptr::read(self.tail))
}
}
}
}
impl<T> Drop for RawItems<T> {
#[unsafe_destructor_blind_to_params]
fn drop(&mut self) {
for _ in self {}
}
}
impl<K, V> Drop for Node<K, V> {
#[unsafe_destructor_blind_to_params]
fn drop(&mut self) {
if self.keys.is_null() ||
(unsafe { self.keys.get() as *const K as usize == mem::POST_DROP_USIZE }) {
// Since we have #[unsafe_no_drop_flag], we have to watch
// out for the sentinel value being stored in self.keys. (Using
// null is technically a violation of the `Unique`
// requirements, though.)
return;
}
// Do the actual cleanup.
unsafe {
drop(RawItems::from_slice(self.keys()));
drop(RawItems::from_slice(self.vals()));
drop(RawItems::from_slice(self.edges()));
self.destroy();
}
self.keys = unsafe { Unique::new(ptr::null_mut()) };
}
}
impl<K, V> Node<K, V> {
/// Make a new internal node. The caller must initialize the result to fix the invariant that
/// there are `len() + 1` edges.
unsafe fn new_internal(capacity: usize) -> Node<K, V> {
let (alignment, size) = calculate_allocation_generic::<K, V>(capacity, false);
let buffer = heap::allocate(size, alignment);
if buffer.is_null() {
::alloc::oom();
}
let (vals_offset, edges_offset) = calculate_offsets_generic::<K, V>(capacity, false);
Node {
keys: Unique::new(buffer as *mut K),
vals: Unique::new(buffer.offset(vals_offset as isize) as *mut V),
edges: Some(Unique::new(buffer.offset(edges_offset as isize) as *mut Node<K, V>)),
_len: 0,
_capacity: capacity,
}
}
/// Make a new leaf node
fn new_leaf(capacity: usize) -> Node<K, V> {
let (alignment, size) = calculate_allocation_generic::<K, V>(capacity, true);
let buffer = unsafe { heap::allocate(size, alignment) };
if buffer.is_null() {
::alloc::oom();
}
let (vals_offset, _) = calculate_offsets_generic::<K, V>(capacity, true);
Node {
keys: unsafe { Unique::new(buffer as *mut K) },
vals: unsafe { Unique::new(buffer.offset(vals_offset as isize) as *mut V) },
edges: None,
_len: 0,
_capacity: capacity,
}
}
unsafe fn destroy(&mut self) {
let (alignment, size) = calculate_allocation_generic::<K, V>(self.capacity(),
self.is_leaf());
heap::deallocate(*self.keys as *mut u8, size, alignment);
}
#[inline]
pub fn as_slices<'a>(&'a self) -> (&'a [K], &'a [V]) {
unsafe {
(slice::from_raw_parts(*self.keys, self.len()),
slice::from_raw_parts(*self.vals, self.len()))
}
}
#[inline]
pub fn as_slices_mut<'a>(&'a mut self) -> (&'a mut [K], &'a mut [V]) {
unsafe {
(slice::from_raw_parts_mut(*self.keys, self.len()),
slice::from_raw_parts_mut(*self.vals, self.len()))
}
}
#[inline]
pub fn as_slices_internal<'b>(&'b self) -> NodeSlice<'b, K, V> {
let is_leaf = self.is_leaf();
let (keys, vals) = self.as_slices();
let edges: &[_] = if self.is_leaf() {
&[]
} else {
unsafe {
let data = match self.edges {
None => heap::EMPTY as *const Node<K, V>,
Some(ref p) => **p as *const Node<K, V>,
};
slice::from_raw_parts(data, self.len() + 1)
}
};
NodeSlice {
keys: keys,
vals: vals,
edges: edges,
head_is_edge: true,
tail_is_edge: true,
has_edges: !is_leaf,
}
}
#[inline]
pub fn as_slices_internal_mut<'b>(&'b mut self) -> MutNodeSlice<'b, K, V> {
let len = self.len();
let is_leaf = self.is_leaf();
let keys = unsafe { slice::from_raw_parts_mut(*self.keys, len) };
let vals = unsafe { slice::from_raw_parts_mut(*self.vals, len) };
let edges: &mut [_] = if is_leaf {
&mut []
} else {
unsafe {
let data = match self.edges {
None => heap::EMPTY as *mut Node<K, V>,
Some(ref mut p) => **p as *mut Node<K, V>,
};
slice::from_raw_parts_mut(data, len + 1)
}
};
MutNodeSlice {
keys: keys,
vals: vals,
edges: edges,
head_is_edge: true,
tail_is_edge: true,
has_edges: !is_leaf,
}
}
#[inline]
pub fn keys<'a>(&'a self) -> &'a [K] {
self.as_slices().0
}
#[inline]
pub fn keys_mut<'a>(&'a mut self) -> &'a mut [K] {
self.as_slices_mut().0
}
#[inline]
pub fn vals<'a>(&'a self) -> &'a [V] {
self.as_slices().1
}
#[inline]
pub fn vals_mut<'a>(&'a mut self) -> &'a mut [V] {
self.as_slices_mut().1
}
#[inline]
pub fn edges<'a>(&'a self) -> &'a [Node<K, V>] {
self.as_slices_internal().edges
}
#[inline]
pub fn edges_mut<'a>(&'a mut self) -> &'a mut [Node<K, V>] {
self.as_slices_internal_mut().edges
}
}
// FIXME(gereeter) Write an efficient clone_from
impl<K: Clone, V: Clone> Clone for Node<K, V> {
fn clone(&self) -> Node<K, V> {
let mut ret = if self.is_leaf() {
Node::new_leaf(self.capacity())
} else {
unsafe { Node::new_internal(self.capacity()) }
};
unsafe {
// For failure safety
let mut keys = RawItems::from_parts(ret.keys().as_ptr(), 0);
let mut vals = RawItems::from_parts(ret.vals().as_ptr(), 0);
let mut edges = RawItems::from_parts(ret.edges().as_ptr(), 0);
for key in self.keys() {
keys.push(key.clone())
}
for val in self.vals() {
vals.push(val.clone())
}
for edge in self.edges() {
edges.push(edge.clone())
}
mem::forget(keys);
mem::forget(vals);
mem::forget(edges);
ret._len = self.len();
}
ret
}
}
/// A reference to something in the middle of a `Node`. There are two `Type`s of `Handle`s,
/// namely `KV` handles, which point to key/value pairs, and `Edge` handles, which point to edges
/// before or after key/value pairs. Methods are provided for removing pairs, inserting into edges,
/// accessing the stored values, and moving around the `Node`.
///
/// This handle is generic, and can take any sort of reference to a `Node`. The reason for this is
/// two-fold. First of all, it reduces the amount of repetitive code, implementing functions that
/// don't need mutability on both mutable and immutable references. Secondly and more importantly,
/// this allows users of the `Handle` API to associate metadata with the reference. This is used in
/// `BTreeMap` to give `Node`s temporary "IDs" that persist to when the `Node` is used in a
/// `Handle`.
///
/// # A note on safety
///
/// Unfortunately, the extra power afforded by being generic also means that safety can technically
/// be broken. For sensible implementations of `Deref` and `DerefMut`, these handles are perfectly
/// safe. As long as repeatedly calling `.deref()` results in the same Node being returned each
/// time, everything should work fine. However, if the `Deref` implementation swaps in multiple
/// different nodes, then the indices that are assumed to be in bounds suddenly stop being so. For
/// example:
///
/// ```rust,ignore
/// struct Nasty<'a> {
/// first: &'a Node<usize, usize>,
/// second: &'a Node<usize, usize>,
/// flag: &'a Cell<bool>,
/// }
///
/// impl<'a> Deref for Nasty<'a> {
/// type Target = Node<usize, usize>;
///
/// fn deref(&self) -> &Node<usize, usize> {
/// if self.flag.get() {
/// &*self.second
/// } else {
/// &*self.first
/// }
/// }
/// }
///
/// fn main() {
/// let flag = Cell::new(false);
/// let mut small_node = Node::make_leaf_root(3);
/// let mut large_node = Node::make_leaf_root(100);
///
/// for i in 0..100 {
/// // Insert to the end
/// large_node.edge_handle(i).insert_as_leaf(i, i);
/// }
///
/// let nasty = Nasty {
/// first: &large_node,
/// second: &small_node,
/// flag: &flag
/// }
///
/// // The handle points at index 75.
/// let handle = Node::search(nasty, 75);
///
/// // Now the handle still points at index 75, but on the small node, which has no index 75.
/// flag.set(true);
///
/// println!("Uninitialized memory: {:?}", handle.into_kv());
/// }
/// ```
#[derive(Copy, Clone)]
pub struct Handle<NodeRef, Type, NodeType> {
node: NodeRef,
index: usize,
marker: PhantomData<(Type, NodeType)>,
}
pub mod handle {
// Handle types.
pub enum KV {}
pub enum Edge {}
// Handle node types.
pub enum LeafOrInternal {}
pub enum Leaf {}
pub enum Internal {}
}
impl<K: Ord, V> Node<K, V> {
/// Searches for the given key in the node. If it finds an exact match,
/// `Found` will be yielded with the matching index. If it doesn't find an exact match,
/// `GoDown` will be yielded with the index of the subtree the key must lie in.
pub fn search<Q: ?Sized, NodeRef: Deref<Target = Node<K, V>>>(node: NodeRef,
key: &Q)
-> SearchResult<NodeRef>
where K: Borrow<Q>,
Q: Ord
{
// FIXME(Gankro): Tune when to search linear or binary based on B (and maybe K/V).
// For the B configured as of this writing (B = 6), binary search was *significantly*
// worse for usizes.
match node.as_slices_internal().search_linear(key) {
(index, true) => {
Found(Handle {
node: node,
index: index,
marker: PhantomData,
})
}
(index, false) => {
GoDown(Handle {
node: node,
index: index,
marker: PhantomData,
})
}
}
}
}
// Public interface
impl<K, V> Node<K, V> {
/// Make a leaf root from scratch
pub fn make_leaf_root(b: usize) -> Node<K, V> {
Node::new_leaf(capacity_from_b(b))
}
/// Make an internal root and swap it with an old root
pub fn make_internal_root(left_and_out: &mut Node<K, V>,
b: usize,
key: K,
value: V,
right: Node<K, V>) {
let node = mem::replace(left_and_out,
unsafe { Node::new_internal(capacity_from_b(b)) });
left_and_out._len = 1;
unsafe {
ptr::write(left_and_out.keys_mut().get_unchecked_mut(0), key);
ptr::write(left_and_out.vals_mut().get_unchecked_mut(0), value);
ptr::write(left_and_out.edges_mut().get_unchecked_mut(0), node);
ptr::write(left_and_out.edges_mut().get_unchecked_mut(1), right);
}
}
/// How many key-value pairs the node contains
pub fn len(&self) -> usize {
self._len
}
/// Does the node not contain any key-value pairs
pub fn is_empty(&self) -> bool {
self.len() == 0
}
/// How many key-value pairs the node can fit
pub fn capacity(&self) -> usize {
self._capacity
}
/// If the node has any children
pub fn is_leaf(&self) -> bool {
self.edges.is_none()
}
/// if the node has too few elements
pub fn is_underfull(&self) -> bool {
self.len() < min_load_from_capacity(self.capacity())
}
/// if the node cannot fit any more elements
pub fn is_full(&self) -> bool {
self.len() == self.capacity()
}
}
impl<K, V, NodeRef: Deref<Target = Node<K, V>>, Type, NodeType> Handle<NodeRef, Type, NodeType> {
/// Returns a reference to the node that contains the pointed-to edge or key/value pair. This
/// is very different from `edge` and `edge_mut` because those return children of the node
/// returned by `node`.
pub fn node(&self) -> &Node<K, V> {
&*self.node
}
}
impl<K, V, NodeRef, Type, NodeType> Handle<NodeRef, Type, NodeType>
where NodeRef: Deref<Target = Node<K, V>> + DerefMut
{
/// Converts a handle into one that stores the same information using a raw pointer. This can
/// be useful in conjunction with `from_raw` when the type system is insufficient for
/// determining the lifetimes of the nodes.
pub fn as_raw(&mut self) -> Handle<*mut Node<K, V>, Type, NodeType> {
Handle {
node: &mut *self.node as *mut _,
index: self.index,
marker: PhantomData,
}
}
}
impl<K, V, Type, NodeType> Handle<*mut Node<K, V>, Type, NodeType> {
/// Converts from a handle stored with a raw pointer, which isn't directly usable, to a handle
/// stored with a reference. This is an unsafe inverse of `as_raw`, and together they allow
/// unsafely extending the lifetime of the reference to the `Node`.
pub unsafe fn from_raw<'a>(&'a self) -> Handle<&'a Node<K, V>, Type, NodeType> {
Handle {
node: &*self.node,
index: self.index,
marker: PhantomData,
}
}
/// Converts from a handle stored with a raw pointer, which isn't directly usable, to a handle
/// stored with a mutable reference. This is an unsafe inverse of `as_raw`, and together they
/// allow unsafely extending the lifetime of the reference to the `Node`.
pub unsafe fn from_raw_mut<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, Type, NodeType> {
Handle {
node: &mut *self.node,
index: self.index,
marker: PhantomData,
}
}
}
impl<'a, K: 'a, V: 'a> Handle<&'a Node<K, V>, handle::Edge, handle::Internal> {
/// Turns the handle into a reference to the edge it points at. This is necessary because the
/// returned pointer has a larger lifetime than what would be returned by `edge` or `edge_mut`,
/// making it more suitable for moving down a chain of nodes.
pub fn into_edge(self) -> &'a Node<K, V> {
unsafe { self.node.edges().get_unchecked(self.index) }
}
}
impl<'a, K: 'a, V: 'a> Handle<&'a mut Node<K, V>, handle::Edge, handle::Internal> {
/// Turns the handle into a mutable reference to the edge it points at. This is necessary
/// because the returned pointer has a larger lifetime than what would be returned by
/// `edge_mut`, making it more suitable for moving down a chain of nodes.
pub fn into_edge_mut(self) -> &'a mut Node<K, V> {
unsafe { self.node.edges_mut().get_unchecked_mut(self.index) }
}
}
impl<K, V, NodeRef: Deref<Target = Node<K, V>>> Handle<NodeRef, handle::Edge, handle::Internal> {
// This doesn't exist because there are no uses for it,
// but is fine to add, analogous to edge_mut.
//
// /// Returns a reference to the edge pointed-to by this handle. This should not be
// /// confused with `node`, which references the parent node of what is returned here.
// pub fn edge(&self) -> &Node<K, V>
}
pub enum ForceResult<NodeRef, Type> {
Leaf(Handle<NodeRef, Type, handle::Leaf>),
Internal(Handle<NodeRef, Type, handle::Internal>),
}
impl<K, V, NodeRef: Deref<Target = Node<K, V>>, Type>
Handle<NodeRef, Type, handle::LeafOrInternal>
{
/// Figure out whether this handle is pointing to something in a leaf node or to something in
/// an internal node, clarifying the type according to the result.
pub fn force(self) -> ForceResult<NodeRef, Type> {
if self.node.is_leaf() {
Leaf(Handle {
node: self.node,
index: self.index,
marker: PhantomData,
})
} else {
Internal(Handle {
node: self.node,
index: self.index,
marker: PhantomData,
})
}
}
}
impl<K, V, NodeRef> Handle<NodeRef, handle::Edge, handle::Leaf>
where NodeRef: Deref<Target = Node<K, V>> + DerefMut
{
/// Tries to insert this key-value pair at the given index in this leaf node
/// If the node is full, we have to split it.
///
/// Returns a *mut V to the inserted value, because the caller may want this when
/// they're done mutating the tree, but we don't want to borrow anything for now.
pub fn insert_as_leaf(mut self, key: K, value: V) -> (InsertionResult<K, V>, *mut V) {
if !self.node.is_full() {
// The element can fit, just insert it
(Fit, unsafe { self.node.insert_kv(self.index, key, value) as *mut _ })
} else {
// The element can't fit, this node is full. Split it into two nodes.
let (new_key, new_val, mut new_right) = self.node.split();
let left_len = self.node.len();
let ptr = unsafe {
if self.index <= left_len {
self.node.insert_kv(self.index, key, value)
} else {
// We need to subtract 1 because in splitting we took out new_key and new_val.
// Just being in the right node means we are past left_len k/v pairs in the
// left node and 1 k/v pair in the parent node.
new_right.insert_kv(self.index - left_len - 1, key, value)
}
} as *mut _;
(Split(new_key, new_val, new_right), ptr)
}
}
}
impl<K, V, NodeRef> Handle<NodeRef, handle::Edge, handle::Internal>
where NodeRef: Deref<Target = Node<K, V>> + DerefMut
{
/// Returns a mutable reference to the edge pointed-to by this handle. This should not be
/// confused with `node`, which references the parent node of what is returned here.
pub fn edge_mut(&mut self) -> &mut Node<K, V> {
unsafe { self.node.edges_mut().get_unchecked_mut(self.index) }
}
/// Tries to insert this key-value pair at the given index in this internal node
/// If the node is full, we have to split it.
pub fn insert_as_internal(mut self,
key: K,
value: V,
right: Node<K, V>)
-> InsertionResult<K, V> {
if !self.node.is_full() {
// The element can fit, just insert it
unsafe {
self.node.insert_kv(self.index, key, value);
self.node.insert_edge(self.index + 1, right); // +1 to insert to the right
}
Fit
} else {
// The element can't fit, this node is full. Split it into two nodes.
let (new_key, new_val, mut new_right) = self.node.split();
let left_len = self.node.len();
if self.index <= left_len {
unsafe {
self.node.insert_kv(self.index, key, value);
self.node.insert_edge(self.index + 1, right); // +1 to insert to the right
}
} else {
unsafe {
// The -1 here is for the same reason as in insert_as_internal - because we
// split, there are actually left_len + 1 k/v pairs before the right node, with
// the extra 1 being put in the parent.
new_right.insert_kv(self.index - left_len - 1, key, value);
new_right.insert_edge(self.index - left_len, right);
}
}
Split(new_key, new_val, new_right)
}
}
/// Handle an underflow in this node's child. We favor handling "to the left" because we know
/// we're empty, but our neighbour can be full. Handling to the left means when we choose to
/// steal, we pop off the end of our neighbour (always fast) and "unshift" ourselves
/// (always slow, but at least faster since we know we're half-empty).
/// Handling "to the right" reverses these roles. Of course, we merge whenever possible
/// because we want dense nodes, and merging is about equal work regardless of direction.
pub fn handle_underflow(mut self) {
unsafe {
if self.index > 0 {
self.handle_underflow_to_left();
} else {
self.handle_underflow_to_right();
}
}
}
/// Right is underflowed. Tries to steal from left,
/// but merges left and right if left is low too.
unsafe fn handle_underflow_to_left(&mut self) {
let left_len = self.node.edges()[self.index - 1].len();
if left_len > min_load_from_capacity(self.node.capacity()) {
self.left_kv().steal_rightward();
} else {
self.left_kv().merge_children();
}
}
/// Left is underflowed. Tries to steal from the right,
/// but merges left and right if right is low too.
unsafe fn handle_underflow_to_right(&mut self) {
let right_len = self.node.edges()[self.index + 1].len();
if right_len > min_load_from_capacity(self.node.capacity()) {
self.right_kv().steal_leftward();
} else {
self.right_kv().merge_children();
}
}
}
impl<K, V, NodeRef, NodeType> Handle<NodeRef, handle::Edge, NodeType>
where NodeRef: Deref<Target = Node<K, V>> + DerefMut
{
/// Gets the handle pointing to the key/value pair just to the left of the pointed-to edge.
/// This is unsafe because the handle might point to the first edge in the node, which has no
/// pair to its left.
unsafe fn left_kv<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, handle::KV, NodeType> {
Handle {
node: &mut *self.node,
index: self.index - 1,
marker: PhantomData,
}
}
/// Gets the handle pointing to the key/value pair just to the right of the pointed-to edge.
/// This is unsafe because the handle might point to the last edge in the node, which has no
/// pair to its right.
unsafe fn right_kv<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, handle::KV, NodeType> {
Handle {
node: &mut *self.node,
index: self.index,
marker: PhantomData,
}
}
}
impl<'a, K: 'a, V: 'a, NodeType> Handle<&'a Node<K, V>, handle::KV, NodeType> {
/// Turns the handle into references to the key and value it points at. This is necessary
/// because the returned pointers have larger lifetimes than what would be returned by `key`
/// or `val`.
pub fn into_kv(self) -> (&'a K, &'a V) {
let (keys, vals) = self.node.as_slices();
unsafe {
(keys.get_unchecked(self.index),
vals.get_unchecked(self.index))
}
}
}
impl<'a, K: 'a, V: 'a, NodeType> Handle<&'a mut Node<K, V>, handle::KV, NodeType> {
/// Turns the handle into mutable references to the key and value it points at. This is
/// necessary because the returned pointers have larger lifetimes than what would be returned
/// by `key_mut` or `val_mut`.
pub fn into_kv_mut(self) -> (&'a mut K, &'a mut V) {
let (keys, vals) = self.node.as_slices_mut();
unsafe {
(keys.get_unchecked_mut(self.index),
vals.get_unchecked_mut(self.index))
}
}
/// Convert this handle into one pointing at the edge immediately to the left of the key/value
/// pair pointed-to by this handle. This is useful because it returns a reference with larger
/// lifetime than `left_edge`.
pub fn into_left_edge(self) -> Handle<&'a mut Node<K, V>, handle::Edge, NodeType> {
Handle {
node: &mut *self.node,
index: self.index,
marker: PhantomData,
}
}
}
impl<'a, K: 'a, V: 'a, NodeRef: Deref<Target = Node<K, V>> + 'a, NodeType> Handle<NodeRef,
handle::KV,
NodeType> {
// These are fine to include, but are currently unneeded.
//
// /// Returns a reference to the key pointed-to by this handle. This doesn't return a
// /// reference with a lifetime as large as `into_kv_mut`, but it also does not consume the
// /// handle.
// pub fn key(&'a self) -> &'a K {
// unsafe { self.node.keys().get_unchecked(self.index) }
// }
//
// /// Returns a reference to the value pointed-to by this handle. This doesn't return a
// /// reference with a lifetime as large as `into_kv_mut`, but it also does not consume the
// /// handle.
// pub fn val(&'a self) -> &'a V {
// unsafe { self.node.vals().get_unchecked(self.index) }
// }
}
impl<'a, K: 'a, V: 'a, NodeRef, NodeType> Handle<NodeRef, handle::KV, NodeType>
where NodeRef: 'a + Deref<Target = Node<K, V>> + DerefMut
{
/// Returns a mutable reference to the key pointed-to by this handle. This doesn't return a
/// reference with a lifetime as large as `into_kv_mut`, but it also does not consume the
/// handle.
pub fn key_mut(&'a mut self) -> &'a mut K {
unsafe { self.node.keys_mut().get_unchecked_mut(self.index) }
}
/// Returns a mutable reference to the value pointed-to by this handle. This doesn't return a
/// reference with a lifetime as large as `into_kv_mut`, but it also does not consume the
/// handle.
pub fn val_mut(&'a mut self) -> &'a mut V {
unsafe { self.node.vals_mut().get_unchecked_mut(self.index) }
}
}
impl<K, V, NodeRef, NodeType> Handle<NodeRef, handle::KV, NodeType>
where NodeRef: Deref<Target = Node<K, V>> + DerefMut
{
/// Gets the handle pointing to the edge immediately to the left of the key/value pair pointed
/// to by this handle.
pub fn left_edge<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, handle::Edge, NodeType> {
Handle {
node: &mut *self.node,
index: self.index,
marker: PhantomData,
}
}
/// Gets the handle pointing to the edge immediately to the right of the key/value pair pointed
/// to by this handle.
pub fn right_edge<'a>(&'a mut self) -> Handle<&'a mut Node<K, V>, handle::Edge, NodeType> {
Handle {