93 lines
1.7 KiB
Go
93 lines
1.7 KiB
Go
// Copyright 2016 by Sascha L. Teichmann
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// Use of this source code is governed by the MIT license
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// that can be found in the LICENSE file.
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package common
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import (
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"bytes"
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"sync"
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)
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type btKey struct {
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x int
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y int
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}
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type btHashEntry struct {
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prev *btHashEntry
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next *btHashEntry
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hash []byte
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btKey
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}
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type BaseTileHash struct {
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hashes map[btKey]*btHashEntry
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maxEntries int
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root btHashEntry
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sync.Mutex
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}
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func NewBaseTileHash(maxEntries int) *BaseTileHash {
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bth := &BaseTileHash{
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hashes: map[btKey]*btHashEntry{},
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maxEntries: maxEntries}
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bth.root.next = &bth.root
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bth.root.prev = &bth.root
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return bth
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}
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func (bth *BaseTileHash) toFront(entry *btHashEntry) {
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if bth.root.next == entry {
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return
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}
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entry.prev.next = entry.next
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entry.next.prev = entry.prev
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entry.next = bth.root.next
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entry.prev = &bth.root
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bth.root.next.prev = entry
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bth.root.next = entry
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}
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func (bth *BaseTileHash) removeLast() *btHashEntry {
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last := bth.root.prev
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bth.root.prev = last.prev
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last.prev.next = &bth.root
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delete(bth.hashes, last.btKey)
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return last
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}
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func (bth *BaseTileHash) insertFront(entry *btHashEntry) {
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entry.next = bth.root.next
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entry.prev = &bth.root
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bth.root.next.prev = entry
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bth.root.next = entry
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}
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func (bth *BaseTileHash) Update(x, y int, hash []byte) bool {
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bth.Lock()
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defer bth.Unlock()
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key := btKey{x, y}
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if old, found := bth.hashes[key]; found {
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if !bytes.Equal(old.hash, hash) {
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old.hash = hash
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bth.toFront(old)
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return true
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}
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return false
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}
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var entry *btHashEntry
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if len(bth.hashes) >= bth.maxEntries {
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entry = bth.removeLast()
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} else {
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entry = new(btHashEntry)
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}
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entry.btKey = key
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entry.hash = hash
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bth.hashes[key] = entry
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bth.insertFront(entry)
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return true
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}
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