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Clarify reuse of a BTreeMap insert support function and treat split support likewise #75058

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Aug 4, 2020
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Clarify reuse of a BTreeMap insert support function and treat split support likewise #75058

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86 changes: 42 additions & 44 deletions library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -819,13 +819,13 @@ impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, mar
}
}

impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
impl<'a, K, V, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::Edge> {
/// Helps implementations of `insert_fit` for a particular `NodeType`,
/// by taking care of leaf data.
/// 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 {
fn leafy_insert_fit(&mut self, key: K, val: V) {
// Necessary for correctness, but in a private module
debug_assert!(self.node.len() < CAPACITY);

Expand All @@ -834,11 +834,23 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge
slice_insert(self.node.vals_mut(), self.idx, val);

(*self.node.as_leaf_mut()).len += 1;

self.node.vals_mut().get_unchecked_mut(self.idx)
}
}
}

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 {
self.leafy_insert_fit(key, val);
unsafe { self.node.vals_mut().get_unchecked_mut(self.idx) }
}
}

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 splits the node if there isn't enough room.
///
Expand Down Expand Up @@ -880,14 +892,6 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
}
}

/// Unsafely asserts to the compiler some static information about whether the underlying
/// node of this handle is a `Leaf` or an `Internal`.
unsafe fn cast_unchecked<NewType>(
&mut self,
) -> Handle<NodeRef<marker::Mut<'_>, K, V, NewType>, marker::Edge> {
unsafe { 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.
Expand All @@ -897,8 +901,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
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);
self.leafy_insert_fit(key, val);

slice_insert(
slice::from_raw_parts_mut(
Expand Down Expand Up @@ -994,18 +997,11 @@ impl<'a, K, V, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker
}
}

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) -> (NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, K, V, Root<K, V>) {
impl<'a, K, V, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
/// Helps implementations of `split` for a particular `NodeType`,
/// by taking care of leaf data.
fn leafy_split(&mut self, new_node: &mut LeafNode<K, V>) -> (K, V, usize) {
unsafe {
let mut new_node = Box::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));

Expand All @@ -1024,6 +1020,24 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV>

(*self.node.as_leaf_mut()).len = self.idx as u16;
new_node.len = new_len as u16;
(k, v, new_len)
}
}
}

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) -> (NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, K, V, Root<K, V>) {
unsafe {
let mut new_node = Box::new(LeafNode::new());

let (k, v, _) = self.leafy_split(&mut new_node);

(self.node, k, v, Root { node: BoxedNode::from_leaf(new_node), height: 0 })
}
Expand Down Expand Up @@ -1055,31 +1069,15 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
unsafe {
let mut new_node = Box::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 (k, v, new_len) = self.leafy_split(&mut new_node.data);
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) {
Expand Down