artful 0.1.1

Low-memory overhead and high-performance adaptive radix tree
Documentation 
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use crate::node::ArtNode;
use crate::node48::Node48;
use crate::ArtKey;
use crate::Header;

const FULL_NODE_SIZE: u16 = 256;

pub(crate) struct Node256<K: ArtKey, V, const MAX_PARTIAL_LEN: usize> {
    pub(crate) header: Header<MAX_PARTIAL_LEN>,
    pub(crate) children: [ArtNode<K, V, MAX_PARTIAL_LEN>; 256],
    pub(crate) prefixed_child: ArtNode<K, V, MAX_PARTIAL_LEN>,
}

impl<K: ArtKey, V, const MAX_PARTIAL_LEN: usize> Default for Node256<K, V, MAX_PARTIAL_LEN> {
    fn default() -> Node256<K, V, MAX_PARTIAL_LEN> {
        // Why dont' i use macro `vec![]` initialize the children?
        // just like, you know `vec![ArtNode::none(); 16].try_into()...`.
        // because it need clone and our intilization with occur on
        // the insert critial performacne path. so, we manual do it.
        Node256 {
            header: Default::default(),
            prefixed_child: ArtNode::default(),
            children: [
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                // 32
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                //64
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                //96
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                // 128
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                // 160
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                // 192
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                // 224
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                ArtNode::none(),
                // 256
            ],
        }
    }
}

impl<K: ArtKey, V, const MAX_PARTIAL_LEN: usize> Node256<K, V, MAX_PARTIAL_LEN> {
    #[inline(always)]
    pub(crate) fn is_full(&self) -> bool {
        self.header.non_null_children == FULL_NODE_SIZE
    }

    #[inline(always)]
    pub(crate) fn minimum_child(&self) -> Option<&ArtNode<K, V, MAX_PARTIAL_LEN>> {
        if !self.prefixed_child.is_none() {
            return Some(&self.prefixed_child);
        }
        // TODO: simd split
        for node in self.children.iter() {
            if !node.is_none() {
                return Some(node);
            }
        }
        return None;
    }

    #[inline]
    pub(crate) fn get_child(&self, key: (u8, bool)) -> Option<&ArtNode<K, V, MAX_PARTIAL_LEN>> {
        if !key.1 {
            return Some(&self.prefixed_child);
        }

        return Some(&self.children[key.0 as usize]);
    }

    pub(crate) fn get_mut_child(
        &mut self,
        key: (u8, bool),
    ) -> Option<&mut ArtNode<K, V, MAX_PARTIAL_LEN>> {
        if !key.1 {
            return Some(&mut self.prefixed_child);
        }

        return Some(&mut self.children[key.0 as usize]);
    }

    /// Safety: grow.
    pub(crate) fn insert_child(
        &mut self,
        key: (u8, bool),
        mut new_child: ArtNode<K, V, MAX_PARTIAL_LEN>,
    ) {
        assert_eq!(self.header.non_null_children, 48);
        let mut assert_cnt = 0;
        for child in self.children.iter() {
            if !child.is_none() {
                assert_cnt += 1;
            }
        }
        assert_eq!(assert_cnt, self.header.non_null_children);

        if !key.1 {
            assert!(self.prefixed_child.is_none());
            std::mem::swap(&mut self.prefixed_child, &mut new_child);
            return;
        }
        self.header.non_null_children += 1;
        std::mem::swap(&mut self.children[key.0 as usize], &mut new_child);
        assert_eq!(new_child.is_none(), true);
        assert_eq!(self.children[key.0 as usize].is_none(), false);
    }

    pub fn is_few(&self) -> bool {
        self.header.non_null_children < 48
    }

    pub(crate) fn remove_child(
        &mut self,
        valid_key: (u8, bool),
    ) -> Option<ArtNode<K, V, MAX_PARTIAL_LEN>> {
        if !valid_key.1 {
            let child = std::mem::take(&mut self.prefixed_child);
            return Some(child);
        }

        self.header.non_null_children -= 1;
        Some(std::mem::take(&mut self.children[valid_key.0 as usize]))
    }

    pub(crate) fn shrink_to_fit(&mut self) -> Box<Node48<K, V, MAX_PARTIAL_LEN>> {
        let mut node48: Box<Node48<K, V, MAX_PARTIAL_LEN>> = Box::default();
        let mut node48_index = 0;

        for (idx, child) in self.children.iter_mut().enumerate() {
            if !child.is_none() {
                std::mem::swap(child, &mut node48.children[node48_index]);
                node48.child_index[idx] = node48_index as u8;
                node48_index += 1;
            }
        }

        std::mem::swap(&mut self.prefixed_child, &mut node48.prefixed_child);
        // node48.header = self.header;
        node48.header.partial.clone_from(&self.header.partial);
        node48.header.non_null_children = node48_index as u16;
        node48
    }
}