1/*
2 * Copyright (C) 2010-2017 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#include "config.h"
27#include "SharedStringHashTableReadOnly.h"
28
29#include "SharedMemory.h"
30
31namespace WebKit {
32
33using namespace WebCore;
34
35#if !ASSERT_DISABLED
36static inline bool isPowerOf2(unsigned v)
37{
38 // Taken from http://www.cs.utk.edu/~vose/c-stuff/bithacks.html
39
40 return !(v & (v - 1)) && v;
41}
42#endif
43
44static inline unsigned doubleHash(unsigned key)
45{
46 key = ~key + (key >> 23);
47 key ^= (key << 12);
48 key ^= (key >> 7);
49 key ^= (key << 2);
50 key ^= (key >> 20);
51 return key;
52}
53
54SharedStringHashTableReadOnly::SharedStringHashTableReadOnly()
55{
56}
57
58SharedStringHashTableReadOnly::~SharedStringHashTableReadOnly()
59{
60}
61
62void SharedStringHashTableReadOnly::setSharedMemory(RefPtr<SharedMemory>&& sharedMemory)
63{
64 m_sharedMemory = WTFMove(sharedMemory);
65
66 if (m_sharedMemory) {
67 ASSERT(!(m_sharedMemory->size() % sizeof(SharedStringHash)));
68 m_table = static_cast<SharedStringHash*>(m_sharedMemory->data());
69 m_tableSize = m_sharedMemory->size() / sizeof(SharedStringHash);
70 ASSERT(isPowerOf2(m_tableSize));
71 m_tableSizeMask = m_tableSize - 1;
72 } else {
73 m_table = nullptr;
74 m_tableSize = 0;
75 m_tableSizeMask = 0;
76 }
77}
78
79bool SharedStringHashTableReadOnly::contains(SharedStringHash sharedStringHash) const
80{
81 auto* slot = findSlot(sharedStringHash);
82 return slot && *slot;
83}
84
85SharedStringHash* SharedStringHashTableReadOnly::findSlot(SharedStringHash sharedStringHash) const
86{
87 if (!m_sharedMemory)
88 return nullptr;
89
90 int k = 0;
91 SharedStringHash* table = m_table;
92 int sizeMask = m_tableSizeMask;
93 unsigned h = static_cast<unsigned>(sharedStringHash);
94 int i = h & sizeMask;
95
96 SharedStringHash* entry;
97 while (1) {
98 entry = table + i;
99
100 // Check if we've reached the end of the table.
101 if (!*entry)
102 return entry;
103
104 if (*entry == sharedStringHash)
105 return entry;
106
107 if (!k)
108 k = 1 | doubleHash(h);
109 i = (i + k) & sizeMask;
110 }
111}
112
113} // namespace WebKit
114