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