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/*
* Copyright (C) 2010-2017 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.
*/
#include "config.h"
#include "SharedStringHashTableReadOnly.h"
#include <WebCore/SharedMemory.h>
#include <wtf/StdLibExtras.h>
namespace WebKit {
using namespace WebCore;
#if ASSERT_ENABLED
static inline bool isPowerOf2(unsigned v)
{
// Taken from http://www.cs.utk.edu/~vose/c-stuff/bithacks.html
return !(v & (v - 1)) && v;
}
#endif
static inline unsigned doubleHash(unsigned key)
{
key = ~key + (key >> 23);
key ^= (key << 12);
key ^= (key >> 7);
key ^= (key << 2);
key ^= (key >> 20);
return key;
}
SharedStringHashTableReadOnly::SharedStringHashTableReadOnly() = default;
SharedStringHashTableReadOnly::~SharedStringHashTableReadOnly() = default;
void SharedStringHashTableReadOnly::setSharedMemory(RefPtr<SharedMemory>&& sharedMemory)
{
m_sharedMemory = WTFMove(sharedMemory);
if (m_sharedMemory) {
ASSERT(!(m_sharedMemory->size() % sizeof(SharedStringHash)));
m_table = spanReinterpretCast<SharedStringHash>(m_sharedMemory->mutableSpan());
ASSERT(isPowerOf2(m_table.size()));
m_tableSizeMask = m_table.size() - 1;
} else {
m_table = { };
m_tableSizeMask = 0;
}
}
bool SharedStringHashTableReadOnly::contains(SharedStringHash sharedStringHash) const
{
auto* slot = findSlot(sharedStringHash);
return slot && *slot;
}
SharedStringHash* SharedStringHashTableReadOnly::findSlot(SharedStringHash sharedStringHash) const
{
if (!m_sharedMemory)
return nullptr;
int k = 0;
auto table = m_table;
int sizeMask = m_tableSizeMask;
unsigned h = static_cast<unsigned>(sharedStringHash);
int i = h & sizeMask;
while (1) {
auto& entry = table[i];
// Check if we've reached the end of the table.
if (!entry)
return &entry;
if (entry == sharedStringHash)
return &entry;
if (!k)
k = 1 | doubleHash(h);
i = (i + k) & sizeMask;
}
}
} // namespace WebKit
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