1/*
2 * Copyright (C) 2010, 2016 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
14 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
15 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
17 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
18 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
19 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
20 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
21 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
22 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
23 * THE POSSIBILITY OF SUCH DAMAGE.
24 */
25
26#pragma once
27
28#include <wtf/NeverDestroyed.h>
29#include <wtf/Vector.h>
30
31namespace WTF {
32
33template<typename KeyType, typename ValueType>
34struct TinyLRUCachePolicy {
35 static bool isKeyNull(const KeyType&) { return false; }
36 static ValueType createValueForNullKey() { return { }; }
37 static ValueType createValueForKey(const KeyType&) { return { }; }
38};
39
40template<typename KeyType, typename ValueType, size_t capacity = 4, typename Policy = TinyLRUCachePolicy<KeyType, ValueType>>
41class TinyLRUCache {
42public:
43 const ValueType& get(const KeyType& key)
44 {
45 if (Policy::isKeyNull(key)) {
46 static NeverDestroyed<ValueType> valueForNull = Policy::createValueForNullKey();
47 return valueForNull;
48 }
49
50 for (size_t i = 0; i < m_cache.size(); ++i) {
51 if (m_cache[i].first != key)
52 continue;
53
54 if (i == m_cache.size() - 1)
55 return m_cache[i].second;
56
57 // If the entry is not the last one, move it to the end of the cache.
58 Entry entry = WTFMove(m_cache[i]);
59 m_cache.remove(i);
60 m_cache.append(WTFMove(entry));
61 return m_cache[m_cache.size() - 1].second;
62 }
63
64 // m_cache[0] is the LRU entry, so remove it.
65 if (m_cache.size() == capacity)
66 m_cache.remove(0);
67
68 m_cache.append(std::make_pair(key, Policy::createValueForKey(key)));
69 return m_cache.last().second;
70 }
71
72private:
73 typedef std::pair<KeyType, ValueType> Entry;
74 typedef Vector<Entry, capacity> Cache;
75 Cache m_cache;
76};
77
78}
79
80using WTF::TinyLRUCache;
81using WTF::TinyLRUCachePolicy;
82