111 lines
2.5 KiB
Go
111 lines
2.5 KiB
Go
// Copyright 2023-2024 The NATS Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package stree
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// Node with 48 children
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// Memory saving vs node256 comes from the fact that the child array is 16 bytes
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// per `node` entry, so node256's 256*16=4096 vs node48's 256+(48*16)=1024
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// Note that `key` is effectively 1-indexed, as 0 means no entry, so offset by 1
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// Order of struct fields for best memory alignment (as per govet/fieldalignment)
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type node48 struct {
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child [48]node
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meta
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key [256]byte
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}
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func newNode48(prefix []byte) *node48 {
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nn := &node48{}
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nn.setPrefix(prefix)
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return nn
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}
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func (n *node48) addChild(c byte, nn node) {
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if n.size >= 48 {
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panic("node48 full!")
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}
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n.child[n.size] = nn
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n.key[c] = byte(n.size + 1) // 1-indexed
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n.size++
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}
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func (n *node48) findChild(c byte) *node {
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i := n.key[c]
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if i == 0 {
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return nil
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}
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return &n.child[i-1]
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}
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func (n *node48) isFull() bool { return n.size >= 48 }
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func (n *node48) grow() node {
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nn := newNode256(n.prefix)
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for c := 0; c < len(n.key); c++ {
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if i := n.key[byte(c)]; i > 0 {
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nn.addChild(byte(c), n.child[i-1])
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}
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}
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return nn
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}
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// Deletes a child from the node.
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func (n *node48) deleteChild(c byte) {
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i := n.key[c]
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if i == 0 {
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return
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}
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i-- // Adjust for 1-indexing
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last := byte(n.size - 1)
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if i < last {
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n.child[i] = n.child[last]
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for ic := 0; ic < len(n.key); ic++ {
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if n.key[byte(ic)] == last+1 {
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n.key[byte(ic)] = i + 1
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break
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}
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}
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}
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n.child[last] = nil
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n.key[c] = 0
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n.size--
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}
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// Shrink if needed and return new node, otherwise return nil.
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func (n *node48) shrink() node {
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if n.size > 16 {
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return nil
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}
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nn := newNode16(nil)
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for c := 0; c < len(n.key); c++ {
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if i := n.key[byte(c)]; i > 0 {
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nn.addChild(byte(c), n.child[i-1])
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}
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}
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return nn
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}
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// Iterate over all children calling func f.
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func (n *node48) iter(f func(node) bool) {
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for _, c := range n.child {
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if c != nil && !f(c) {
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return
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}
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}
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}
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// Return our children as a slice.
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func (n *node48) children() []node {
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return n.child[:n.size]
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}
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