84 lines
3.1 KiB
C++
84 lines
3.1 KiB
C++
/*
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* Copyright (C) 2010, 2016 Apple Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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* THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <wtf/NeverDestroyed.h>
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#include <wtf/Vector.h>
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namespace WTF {
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template<typename KeyType, typename ValueType>
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struct TinyLRUCachePolicy {
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static bool isKeyNull(const KeyType&) { return false; }
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static ValueType createValueForNullKey() { return { }; }
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static ValueType createValueForKey(const KeyType&) { return { }; }
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static KeyType createKeyForStorage(const KeyType& key) { return key; }
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};
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template<typename KeyType, typename ValueType, size_t capacity = 4, typename Policy = TinyLRUCachePolicy<KeyType, ValueType>>
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class TinyLRUCache {
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WTF_MAKE_FAST_ALLOCATED;
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public:
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const ValueType& get(const KeyType& key)
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{
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if (Policy::isKeyNull(key)) {
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static NeverDestroyed<ValueType> valueForNull = Policy::createValueForNullKey();
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return valueForNull;
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}
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for (size_t i = 0; i < m_cache.size(); ++i) {
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if (m_cache[i].first != key)
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continue;
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if (i == m_cache.size() - 1)
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return m_cache[i].second;
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// If the entry is not the last one, move it to the end of the cache.
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Entry entry = WTFMove(m_cache[i]);
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m_cache.remove(i);
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m_cache.append(WTFMove(entry));
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return m_cache[m_cache.size() - 1].second;
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}
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// m_cache[0] is the LRU entry, so remove it.
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if (m_cache.size() == capacity)
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m_cache.remove(0);
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m_cache.append(std::make_pair(Policy::createKeyForStorage(key), Policy::createValueForKey(key)));
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return m_cache.last().second;
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}
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private:
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typedef std::pair<KeyType, ValueType> Entry;
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typedef Vector<Entry, capacity> Cache;
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Cache m_cache;
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};
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}
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using WTF::TinyLRUCache;
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using WTF::TinyLRUCachePolicy;
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