84 lines
2.3 KiB
C++
84 lines
2.3 KiB
C++
// Copyright 2022 The Android Open Source Project
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//
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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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#pragma once
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#include <list>
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#include <unordered_map>
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template <typename Key, typename Value>
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class LruCache {
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public:
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LruCache(std::size_t maxSize) : m_maxSize(maxSize) {
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m_table.reserve(maxSize);
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}
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Value* get(const Key& key) {
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auto tableIt = m_table.find(key);
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if (tableIt == m_table.end()) {
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return nullptr;
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}
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// Move to front.
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auto elementsIt = tableIt->second;
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m_elements.splice(elementsIt, m_elements, m_elements.begin());
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return &elementsIt->value;
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}
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void set(const Key& key, Value&& value) {
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auto tableIt = m_table.find(key);
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if (tableIt == m_table.end()) {
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if (m_table.size() >= m_maxSize) {
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auto& kv = m_elements.back();
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m_table.erase(kv.key);
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m_elements.pop_back();
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}
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} else {
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auto elementsIt = tableIt->second;
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m_elements.erase(elementsIt);
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}
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m_elements.emplace_front(KeyValue{
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key,
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std::forward<Value>(value),
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});
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m_table[key] = m_elements.begin();
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}
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void remove(const Key& key) {
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auto tableIt = m_table.find(key);
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if (tableIt == m_table.end()) {
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return;
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}
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auto elementsIt = tableIt->second;
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m_elements.erase(elementsIt);
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m_table.erase(tableIt);
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}
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void clear() {
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m_elements.clear();
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m_table.clear();
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}
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private:
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struct KeyValue {
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Key key;
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Value value;
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};
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const std::size_t m_maxSize;
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// Front is the most recently used and back is the least recently used.
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std::list<KeyValue> m_elements;
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std::unordered_map<Key, typename std::list<KeyValue>::iterator> m_table;
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};
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