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