src/liballoc/collections/btree/search.rs

use core::borrow::Borrow;
use core::cmp::Ordering;

use super::node::{marker, ForceResult::*, Handle, NodeRef};

use SearchResult::*;

pub enum SearchResult<BorrowType, K, V, FoundType, GoDownType> {
    Found(Handle<NodeRef<BorrowType, K, V, FoundType>, marker::KV>),
    GoDown(Handle<NodeRef<BorrowType, K, V, GoDownType>, marker::Edge>),
}

pub fn search_tree<BorrowType, K, V, Q: ?Sized>(
    mut node: NodeRef<BorrowType, K, V, marker::LeafOrInternal>,
    key: &Q,
) -> SearchResult<BorrowType, K, V, marker::LeafOrInternal, marker::Leaf>
where
    Q: Ord,
    K: Borrow<Q>,
{
    loop {
        match search_node(node, key) {
            Found(handle) => return Found(handle),
            GoDown(handle) => match handle.force() {
                Leaf(leaf) => return GoDown(leaf),
                Internal(internal) => {
                    node = internal.descend();
                    continue;
                }
            },
        }
    }
}

pub fn search_node<BorrowType, K, V, Type, Q: ?Sized>(
    node: NodeRef<BorrowType, K, V, Type>,
    key: &Q,
) -> SearchResult<BorrowType, K, V, Type, Type>
where
    Q: Ord,
    K: Borrow<Q>,
{
    match search_linear(&node, key) {
        (idx, true) => Found(Handle::new_kv(node, idx)),
        (idx, false) => SearchResult::GoDown(Handle::new_edge(node, idx)),
    }
}

/// Returns the index in the node at which the key (or an equivalent) exists
/// or could exist, and whether it exists in the node itself. If it doesn't
/// exist in the node itself, it may exist in the subtree with that index
/// (if the node has subtrees). If the key doesn't exist in node or subtree,
/// the returned index is the position or subtree to insert at.
pub fn search_linear<BorrowType, K, V, Type, Q: ?Sized>(
    node: &NodeRef<BorrowType, K, V, Type>,
    key: &Q,
) -> (usize, bool)
where
    Q: Ord,
    K: Borrow<Q>,
{
    // This function is defined over all borrow types (immutable, mutable, owned),
    // and may be called on the shared root in each case.
    // Crucially, we use `keys()` here, i.e., we work with immutable data.
    // `keys_mut()` does not support the shared root, so we cannot use it.
    // Using `keys()` is fine here even if BorrowType is mutable, as all we return
    // is an index -- not a reference.
    for (i, k) in node.keys().iter().enumerate() {
        match key.cmp(k.borrow()) {
            Ordering::Greater => {}
            Ordering::Equal => return (i, true),
            Ordering::Less => return (i, false),
        }
    }
    (node.keys().len(), false)
}