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node.rs
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node.rs
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//! Bookkeeping nodes.
//!
//! This module provides the basic unit in the bookkeeper, the nodes.
/// A block list node.
///
/// A node consists of three components:
///
/// 1. The inner value that the node holds.
/// 2. A pointer to the next node.
/// 3. A stack of so called "shortcuts", which contains data about jumping over/searching for
/// nodes.
struct Node {
/// The inner block.
///
/// This should never be empty (zero-sized).
block: Block,
/// The node that follows this node.
///
/// This cannot be adjacent (tangent) to `self.block`. It is important to maintain the blocks
/// as long as possible, and hence merge if that is the case.
///
/// `None` indicates that the node is the last node in the list.
next: Option<Jar<Node>>,
/// Shortcuts/jumps of the current node.
///
/// This is a stack of linked list nodes, such that any entry has a list which is a superset of
/// the latter. The lowest layer is a subset of the block list itself.
///
/// ...
/// 2 # ---------------------> [6] ---------------------> [9] -------------> NIL
/// 1 # ---------------------> [6] ---> [7] ------------> [9] -------------> NIL
/// 0 # ------------> [5] ---> [6] ---> [7] ------------> [9] ---> [10] ---> NIL
/// bottom # ---> [1] ---> [5] ---> [6] ---> [7] ---> [8] ---> [9] ---> [10] ---> NIL
///
/// As a result the lowest entry is the most dense.
///
/// If we assume our node is `[6]`, the stack would contain shotcuts to 7, 7, and 8, in that
/// order. The rest would simply be null pointers with fat value 0.
///
/// # Height
///
/// The index of the highest null shortcut (or, if none, the length of the array) is called the
/// height of the node.
shortcuts: lv::Array<Shortcut>,
}
impl Jar<Node> {
/// Insert a new node after this node.
fn insert(&mut self, new_node: Jar<Node>) {
// We move out of the pointer temporarily in order to restructure the list.
take::replace_with(self, |node| {
// Place the old node next to the new node.
new_node.next = Some(node);
// Set the new node in the old node's previous place.
new_node
});
}
}
impl Node {
/// Create an iterator over the nodes.
///
/// This iterator starts at `self` and go to `self.next` until it is `None`.
// TODO: Implement `IntoIterator`.
fn iter(&mut self) -> impl Iterator<Item = &Node> {
NodeIter {
node: Some(self),
}
}
/// Create an iterator following the `lv`'th shortcut.
fn follow_shortcut(&self, lv: shotcut::Level) -> impl Iterator<Item = Shortcut> {
ShortcutIter {
lv: lv,
node: Some(self),
}
}