222 lines
6.5 KiB
Go
222 lines
6.5 KiB
Go
// Copyright (c) 2026 Karl Gaissmaier
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// SPDX-License-Identifier: MIT
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package nodes
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import (
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"iter"
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"github.com/gaissmai/bart/internal/bitset"
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"github.com/gaissmai/bart/internal/lpm"
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"github.com/gaissmai/bart/internal/sparse"
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)
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// LiteNode is a space-optimized version of [BartNode] that tracks prefix existence
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// without storing associated values.
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type LiteNode[V any] struct {
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Children sparse.Array256[any]
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Prefixes struct {
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// BitSet256 tracks the presence of prefixes at this level.
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bitset.BitSet256
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// Count maintains the current number of set bits, updated on modification
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// to avoid expensive population counting.
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Count uint16
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}
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}
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// IsEmpty returns true if the node contains no routing entries (prefixes)
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// and no child nodes. Empty nodes are candidates for compression or removal
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// during trie optimization.
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func (n *LiteNode[V]) IsEmpty() bool {
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if n == nil {
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return true
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}
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return n.Prefixes.Count == 0 && n.Children.Len() == 0
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}
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// PrefixCount returns the number of prefixes stored in this node.
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func (n *LiteNode[V]) PrefixCount() int {
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return int(n.Prefixes.Count)
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}
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// ChildCount returns the number of slots used in this node.
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func (n *LiteNode[V]) ChildCount() int {
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return n.Children.Len()
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}
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// InsertPrefix adds a routing entry at the specified index.
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// It returns true if a prefix already existed at that index,
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// false if this is a new insertion.
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func (n *LiteNode[V]) InsertPrefix(idx uint8, _ V) (exists bool) {
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if exists = n.Prefixes.Test(idx); exists {
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return exists
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}
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n.Prefixes.Set(idx)
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n.Prefixes.Count++
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return exists
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}
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func (n *LiteNode[V]) GetPrefix(idx uint8) (_ V, exists bool) {
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// no docstring by intention
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exists = n.Prefixes.Test(idx)
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return
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}
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func (n *LiteNode[V]) MustGetPrefix(idx uint8) (_ V) {
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// no docstring by intention
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return
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}
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// AllIndices returns an iterator over all prefix entries.
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// Each iteration yields the prefix index (uint8) and its associated value (V).
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func (n *LiteNode[V]) AllIndices() iter.Seq2[uint8, V] {
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var zero V
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return func(yield func(uint8, V) bool) {
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var buf [256]uint8
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for _, idx := range n.Prefixes.AsSlice(&buf) {
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if !yield(idx, zero) {
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return
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}
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}
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}
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}
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// DeletePrefix removes the prefix at the specified index.
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// Returns true if the prefix existed, and false otherwise.
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func (n *LiteNode[V]) DeletePrefix(idx uint8) (exists bool) {
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if exists = n.Prefixes.Test(idx); !exists {
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return false
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}
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n.Prefixes.Clear(idx)
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n.Prefixes.Count--
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return true
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}
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// InsertChild adds a child node at the specified address (0-255).
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// The child can be a *LiteNode[V], *LeafNode, or *FringeNode.
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// Returns true if a child already existed at that address.
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func (n *LiteNode[V]) InsertChild(addr uint8, child any) (exists bool) {
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_, exists = n.Children.InsertAt(addr, child)
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return
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}
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// GetChild retrieves the child node at the specified address.
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// Returns the child and true if found, or nil and false if not present.
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func (n *LiteNode[V]) GetChild(addr uint8) (any, bool) {
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return n.Children.Get(addr)
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}
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// MustGetChild retrieves the child at the specified address, panicking if not found.
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// This method should only be used when the caller is certain the child exists.
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func (n *LiteNode[V]) MustGetChild(addr uint8) any {
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return n.Children.MustGet(addr)
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}
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// AllChildren returns an iterator over all child nodes.
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// Each iteration yields the child's address (uint8) and the child node (any).
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func (n *LiteNode[V]) AllChildren() iter.Seq2[uint8, any] {
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return func(yield func(addr uint8, child any) bool) {
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var buf [256]uint8
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addrs := n.Children.AsSlice(&buf)
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for i, addr := range addrs {
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if !yield(addr, n.Children.Items[i]) {
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return
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}
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}
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}
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}
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// DeleteChild removes the child node at the specified address.
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// This operation is idempotent - removing a non-existent child is safe.
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func (n *LiteNode[V]) DeleteChild(addr uint8) (exists bool) {
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_, exists = n.Children.DeleteAt(addr)
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return exists
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}
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// Contains returns true if an index (idx) has any matching longest-prefix
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// in the current node’s prefix table.
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//
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// This function performs a presence check.
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//
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// The prefix table is structured as a complete binary tree (CBT), and LPM testing
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// is done via a bitset operation that maps the traversal path from the given index
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// toward its possible ancestors.
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func (n *LiteNode[V]) Contains(idx uint8) bool {
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return n.Prefixes.Intersects(&lpm.LookupTbl[idx])
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}
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// LookupIdx performs a longest-prefix match (LPM) lookup for the given index (idx)
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// within the 8-bit stride-based prefix table at this trie depth.
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//
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// The function returns the matched index and whether a matching prefix
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// exists at this level. The value type parameter exists only to satisfy interfaces.
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//
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// Internally, the prefix table is organized as a complete binary tree (CBT) indexed
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// via the baseIndex function. Unlike the original ART algorithm, this implementation
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// does not use an allotment-based approach. Instead, it performs CBT backtracking
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// using a bitset-based operation with a precomputed backtracking pattern specific to idx.
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func (n *LiteNode[V]) LookupIdx(idx uint8) (top uint8, _ V, ok bool) {
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top, ok = n.Prefixes.IntersectionTop(&lpm.LookupTbl[idx])
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return
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}
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// Lookup is just a simple wrapper for LookupIdx.
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func (n *LiteNode[V]) Lookup(idx uint8) (_ V, ok bool) {
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_, _, ok = n.LookupIdx(idx)
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return
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}
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// CloneFlat returns a shallow copy of the current node.
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//
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// CloneFn is only used for interface satisfaction.
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func (n *LiteNode[V]) CloneFlat(_ func(V) V) *LiteNode[V] {
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if n == nil {
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return nil
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}
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c := new(LiteNode[V])
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if n.IsEmpty() {
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return c
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}
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// copy simple values
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c.Prefixes = n.Prefixes
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// sparse array
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c.Children = *(n.Children.Copy())
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// no values to copy
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return c
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}
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// CloneRec performs a recursive deep copy of the node and all its descendants.
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//
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// cloneFn is only used for interface satisfaction.
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//
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// It first creates a shallow clone of the current node using CloneFlat.
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// Then it recursively clones all child nodes of type *LiteNode[V],
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// performing a full deep clone down the subtree.
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//
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// Child nodes of type *LeafNode and *FringeNode are already copied
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// by CloneFlat.
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//
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// Returns a new instance of LiteNode[V] which is a complete deep clone of the
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// receiver node with all descendants.
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func (n *LiteNode[V]) CloneRec(_ func(V) V) *LiteNode[V] {
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if n == nil {
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return nil
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}
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// Perform a flat clone of the current node.
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c := n.CloneFlat(nil)
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// Recursively clone all child nodes of type *LiteNode[V]
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for i, kidAny := range c.Children.Items {
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if kid, ok := kidAny.(*LiteNode[V]); ok {
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c.Children.Items[i] = kid.CloneRec(nil)
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}
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}
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return c
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}
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