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A `node256` is nearly 4KB in memory whereas a `node48` is closer to 1KB. Signed-off-by: Neil Twigg <neil@nats.io>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,110 @@ | ||
| // 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 | ||
|
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||
| // 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 | ||
| } | ||
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| func newNode48(prefix []byte) *node48 { | ||
| nn := &node48{} | ||
| nn.setPrefix(prefix) | ||
| return nn | ||
| } | ||
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| 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] | ||
| } | ||
|
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| func (n *node48) isFull() bool { return n.size >= 48 } | ||
|
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| func (n *node48) grow() node { | ||
| nn := newNode256(n.prefix) | ||
| for c := byte(0); c < 255; c++ { | ||
| if i := n.key[c]; i > 0 { | ||
| nn.addChild(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 c := byte(0); c <= 255; c++ { | ||
| if n.key[c] == last+1 { | ||
| n.key[c] = i + 1 | ||
| break | ||
| } | ||
| } | ||
| } | ||
| n.child[last] = nil | ||
| n.key[c] = 0 | ||
| n.size-- | ||
| } | ||
|
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| // 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 := byte(0); c < 255; c++ { | ||
| if i := n.key[c]; i > 0 { | ||
| nn.addChild(c, n.child[i-1]) | ||
| } | ||
| } | ||
| return nn | ||
| } | ||
|
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| // 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 | ||
| } | ||
| } | ||
| } | ||
|
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||
| // Return our children as a slice. | ||
| func (n *node48) children() []node { | ||
| return n.child[:n.size] | ||
| } |
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