Method prev

cranelift/bforest/src/path.rs:133–159

Move this path to the previous key-value pair and return it. If the path is at the off-the-end position, go to the last key-value pair. If the path is already at the first key-value pair, leave it there and return `None`.

(&mut self, root: Node, pool: &NodePool<F>)

    ///
    /// If the path is already at the first key-value pair, leave it there and return `None`.
    pub fn prev(&mut self, root: Node, pool: &NodePool<F>) -> Option<(F::Key, F::Value)> {
        // We use `size == 0` as a generic off-the-end position.
        if self.size == 0 {
            self.goto_subtree_last(0, root, pool);
            let (node, entry) = self.leaf_pos().unwrap();
            let (keys, vals) = pool[node].unwrap_leaf();
            return Some((keys[entry], vals[entry]));
        }

        match self.leaf_pos() {
            None => return None,
            Some((node, entry)) => {
                if entry > 0 {
                    self.entry[self.size - 1] -= 1;
                    let (keys, vals) = pool[node].unwrap_leaf();
                    return Some((keys[entry - 1], vals[entry - 1]));
                }
            }
        }

        // The current leaf node is exhausted. Move to the previous one.
        self.prev_leaf(pool).map(|node| {
            let (keys, vals) = pool[node].unwrap_leaf();
            let e = self.leaf_entry();
            (keys[e], vals[e])
        })
    }

    /// Move path to the first entry of the next node at level, if one exists.
    ///