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BTreeMap: more expressive local variables in merge #80006

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Dec 17, 2020
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BTreeMap: more expressive local variables in merge #80006

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55 changes: 27 additions & 28 deletions library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1352,66 +1352,65 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
///
/// Panics unless we `.can_merge()`.
pub fn merge(
mut self,
self,
track_edge_idx: Option<LeftOrRight<usize>>,
) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Edge> {
let Handle { node: mut parent_node, idx: parent_idx, _marker } = self.parent;
let old_parent_len = parent_node.len();
let mut left_node = self.left_child;
let left_len = left_node.len();
let old_left_len = left_node.len();
let right_node = self.right_child;
let right_len = right_node.len();
let new_left_len = old_left_len + 1 + right_len;

assert!(left_len + right_len < CAPACITY);
assert!(new_left_len <= CAPACITY);
assert!(match track_edge_idx {
None => true,
Some(LeftOrRight::Left(idx)) => idx <= left_len,
Some(LeftOrRight::Left(idx)) => idx <= old_left_len,
Some(LeftOrRight::Right(idx)) => idx <= right_len,
});

unsafe {
*left_node.reborrow_mut().into_len_mut() += right_len as u16 + 1;
*left_node.reborrow_mut().into_len_mut() = new_left_len as u16;

let parent_key = slice_remove(
self.parent.node.reborrow_mut().into_key_area_slice(),
self.parent.idx,
);
left_node.reborrow_mut().into_key_area_mut_at(left_len).write(parent_key);
let parent_key =
slice_remove(parent_node.reborrow_mut().into_key_area_slice(), parent_idx);
left_node.reborrow_mut().into_key_area_mut_at(old_left_len).write(parent_key);
ptr::copy_nonoverlapping(
right_node.reborrow().key_area().as_ptr(),
left_node.reborrow_mut().into_key_area_slice().as_mut_ptr().add(left_len + 1),
left_node.reborrow_mut().into_key_area_slice().as_mut_ptr().add(old_left_len + 1),
right_len,
);

let parent_val = slice_remove(
self.parent.node.reborrow_mut().into_val_area_slice(),
self.parent.idx,
);
left_node.reborrow_mut().into_val_area_mut_at(left_len).write(parent_val);
let parent_val =
slice_remove(parent_node.reborrow_mut().into_val_area_slice(), parent_idx);
left_node.reborrow_mut().into_val_area_mut_at(old_left_len).write(parent_val);
ptr::copy_nonoverlapping(
right_node.reborrow().val_area().as_ptr(),
left_node.reborrow_mut().into_val_area_slice().as_mut_ptr().add(left_len + 1),
left_node.reborrow_mut().into_val_area_slice().as_mut_ptr().add(old_left_len + 1),
right_len,
);

slice_remove(
&mut self.parent.node.reborrow_mut().into_edge_area_slice(),
self.parent.idx + 1,
);
let parent_old_len = self.parent.node.len();
self.parent.node.correct_childrens_parent_links(self.parent.idx + 1..parent_old_len);
*self.parent.node.reborrow_mut().into_len_mut() -= 1;
slice_remove(&mut parent_node.reborrow_mut().into_edge_area_slice(), parent_idx + 1);
parent_node.correct_childrens_parent_links(parent_idx + 1..old_parent_len);
*parent_node.reborrow_mut().into_len_mut() -= 1;

if self.parent.node.height > 1 {
if parent_node.height > 1 {
// SAFETY: the height of the nodes being merged is one below the height
// of the node of this edge, thus above zero, so they are internal.
let mut left_node = left_node.reborrow_mut().cast_to_internal_unchecked();
let right_node = right_node.cast_to_internal_unchecked();
ptr::copy_nonoverlapping(
right_node.reborrow().edge_area().as_ptr(),
left_node.reborrow_mut().into_edge_area_slice().as_mut_ptr().add(left_len + 1),
left_node
.reborrow_mut()
.into_edge_area_slice()
.as_mut_ptr()
.add(old_left_len + 1),
right_len + 1,
);

left_node.correct_childrens_parent_links(left_len + 1..=left_len + 1 + right_len);
left_node.correct_childrens_parent_links(old_left_len + 1..new_left_len + 1);

Global.deallocate(right_node.node.cast(), Layout::new::<InternalNode<K, V>>());
} else {
Expand All @@ -1421,7 +1420,7 @@ impl<'a, K: 'a, V: 'a> BalancingContext<'a, K, V> {
let new_idx = match track_edge_idx {
None => 0,
Some(LeftOrRight::Left(idx)) => idx,
Some(LeftOrRight::Right(idx)) => left_len + 1 + idx,
Some(LeftOrRight::Right(idx)) => old_left_len + 1 + idx,
};
Handle::new_edge(left_node, new_idx)
}
Expand Down