1use super::node::{ForceResult::*, Root};
2use super::search::SearchResult::*;
3use core::alloc::Allocator;
4use core::borrow::Borrow;
5
6impl<K, V> Root<K, V> {
7 /// Calculates the length of both trees that result from splitting up
8 /// a given number of distinct key-value pairs.
9 pub fn calc_split_length(
10 total_num: usize,
11 root_a: &Root<K, V>,
12 root_b: &Root<K, V>,
13 ) -> (usize, usize) {
14 let (length_a, length_b);
15 if root_a.height() < root_b.height() {
16 length_a = root_a.reborrow().calc_length();
17 length_b = total_num - length_a;
18 debug_assert_eq!(length_b, root_b.reborrow().calc_length());
19 } else {
20 length_b = root_b.reborrow().calc_length();
21 length_a = total_num - length_b;
22 debug_assert_eq!(length_a, root_a.reborrow().calc_length());
23 }
24 (length_a, length_b)
25 }
26
27 /// Split off a tree with key-value pairs at and after the given key.
28 /// The result is meaningful only if the tree is ordered by key,
29 /// and if the ordering of `Q` corresponds to that of `K`.
30 /// If `self` respects all `BTreeMap` tree invariants, then both
31 /// `self` and the returned tree will respect those invariants.
32 pub fn split_off<Q: ?Sized + Ord, A: Allocator + Clone>(&mut self, key: &Q, alloc: A) -> Self
33 where
34 K: Borrow<Q>,
35 {
36 let left_root = self;
37 let mut right_root = Root::new_pillar(left_root.height(), alloc.clone());
38 let mut left_node = left_root.borrow_mut();
39 let mut right_node = right_root.borrow_mut();
40
41 loop {
42 let mut split_edge = match left_node.search_node(key) {
43 // key is going to the right tree
44 Found(kv) => kv.left_edge(),
45 GoDown(edge) => edge,
46 };
47
48 split_edge.move_suffix(&mut right_node);
49
50 match (split_edge.force(), right_node.force()) {
51 (Internal(edge), Internal(node)) => {
52 left_node = edge.descend();
53 right_node = node.first_edge().descend();
54 }
55 (Leaf(_), Leaf(_)) => break,
56 _ => unreachable!(),
57 }
58 }
59
60 left_root.fix_right_border(alloc.clone());
61 right_root.fix_left_border(alloc);
62 right_root
63 }
64
65 /// Creates a tree consisting of empty nodes.
66 fn new_pillar<A: Allocator + Clone>(height: usize, alloc: A) -> Self {
67 let mut root = Root::new(alloc.clone());
68 for _ in 0..height {
69 root.push_internal_level(alloc.clone());
70 }
71 root
72 }
73}
74

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