289 lines
8.8 KiB
C++
289 lines
8.8 KiB
C++
/*
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* Copyright (C) 2019 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. ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
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* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
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* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <array>
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#include <wtf/Forward.h>
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#include <wtf/GetPtr.h>
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#include <wtf/HashFunctions.h>
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#include <wtf/MathExtras.h>
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#include <wtf/StdLibExtras.h>
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#include <wtf/UnalignedAccess.h>
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#if OS(DARWIN)
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#include <mach/vm_param.h>
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#endif
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namespace WTF {
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template<typename T>
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class Packed {
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WTF_MAKE_FAST_ALLOCATED;
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public:
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static constexpr bool isPackedType = true;
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Packed()
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: Packed(T { })
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{
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}
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Packed(const T& value)
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{
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unalignedStore<T>(m_storage.data(), value);
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}
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T get() const
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{
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return unalignedLoad<T>(m_storage.data());
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}
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void set(const T& value)
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{
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unalignedStore<T>(m_storage.data(), value);
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}
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Packed<T>& operator=(const T& value)
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{
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set(value);
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return *this;
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}
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template<class U>
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T exchange(U&& newValue)
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{
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T oldValue = get();
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set(std::forward<U>(newValue));
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return oldValue;
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}
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void swap(Packed& other)
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{
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m_storage.swap(other.m_storage);
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}
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template<typename Other, typename = std::enable_if_t<Other::isPackedType>>
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void swap(Other& other)
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{
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T t1 = get();
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T t2 = other.get();
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set(t2);
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other.set(t1);
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}
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void swap(T& t2)
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{
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T t1 = get();
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std::swap(t1, t2);
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set(t1);
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}
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private:
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std::array<uint8_t, sizeof(T)> m_storage;
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};
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// PackedAlignedPtr can take alignment parameter too. PackedAlignedPtr only uses this alignment information if it is profitable: we use
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// alignment information only when we can reduce the size of the storage.
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template<typename T, size_t passedAlignment>
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class PackedAlignedPtr {
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WTF_MAKE_FAST_ALLOCATED;
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public:
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static_assert(hasOneBitSet(passedAlignment), "Alignment needs to be power-of-two");
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static constexpr size_t alignment = passedAlignment;
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static constexpr bool isPackedType = true;
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static constexpr unsigned alignmentShiftSizeIfProfitable = getLSBSetConstexpr(alignment);
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static constexpr unsigned storageSizeWithoutAlignmentShift = roundUpToMultipleOf<8>(OS_CONSTANT(EFFECTIVE_ADDRESS_WIDTH)) / 8;
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static constexpr unsigned storageSizeWithAlignmentShift = roundUpToMultipleOf<8>(OS_CONSTANT(EFFECTIVE_ADDRESS_WIDTH) - alignmentShiftSizeIfProfitable) / 8;
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static constexpr bool isAlignmentShiftProfitable = storageSizeWithoutAlignmentShift > storageSizeWithAlignmentShift;
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static constexpr unsigned alignmentShiftSize = isAlignmentShiftProfitable ? alignmentShiftSizeIfProfitable : 0;
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static constexpr unsigned storageSize = storageSizeWithAlignmentShift;
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static_assert(storageSize <= sizeof(uintptr_t));
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constexpr PackedAlignedPtr()
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: m_storage()
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{
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}
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constexpr PackedAlignedPtr(std::nullptr_t)
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: m_storage()
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{
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}
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PackedAlignedPtr(T* value)
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{
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set(value);
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}
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T* get() const
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{
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// FIXME: PackedPtr<> can load memory with one mov by checking page boundary.
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// https://bugs.webkit.org/show_bug.cgi?id=197754
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uintptr_t value = 0;
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#if CPU(LITTLE_ENDIAN)
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memcpy(&value, m_storage.data(), storageSize);
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#else
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memcpy(bitwise_cast<uint8_t*>(&value) + (sizeof(void*) - storageSize), m_storage.data(), storageSize);
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#endif
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if (isAlignmentShiftProfitable)
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value <<= alignmentShiftSize;
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#if CPU(X86_64) && !(OS(DARWIN) || OS(LINUX) || OS(WINDOWS))
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// The AMD specification requires that the most significant 16
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// bits of any virtual address, bits 48 through 63, must be
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// copies of bit 47 (in a manner akin to sign extension).
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//
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// The above-named OSes will never allocate user space addresses
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// with bit 47 set, thus are already in canonical form.
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//
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// Reference: https://en.wikipedia.org/wiki/X86-64#Virtual_address_space_details
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constexpr unsigned shiftBits = countOfBits<uintptr_t> - OS_CONSTANT(EFFECTIVE_ADDRESS_WIDTH);
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value = (bitwise_cast<intptr_t>(value) << shiftBits) >> shiftBits;
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#endif
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return bitwise_cast<T*>(value);
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}
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void set(T* passedValue)
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{
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uintptr_t value = bitwise_cast<uintptr_t>(passedValue);
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if (isAlignmentShiftProfitable)
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value >>= alignmentShiftSize;
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#if CPU(LITTLE_ENDIAN)
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memcpy(m_storage.data(), &value, storageSize);
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#else
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memcpy(m_storage.data(), bitwise_cast<uint8_t*>(&value) + (sizeof(void*) - storageSize), storageSize);
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#endif
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ASSERT(bitwise_cast<uintptr_t>(get()) == value);
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}
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void clear()
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{
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set(nullptr);
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}
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T* operator->() const { return get(); }
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T& operator*() const { return *get(); }
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bool operator!() const { return !get(); }
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// This conversion operator allows implicit conversion to bool but not to other integer types.
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typedef T* (PackedAlignedPtr::*UnspecifiedBoolType);
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operator UnspecifiedBoolType() const { return get() ? &PackedAlignedPtr::m_storage : nullptr; }
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explicit operator bool() const { return get(); }
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PackedAlignedPtr& operator=(T* value)
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{
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set(value);
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return *this;
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}
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template<class U>
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T* exchange(U&& newValue)
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{
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T* oldValue = get();
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set(std::forward<U>(newValue));
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return oldValue;
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}
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void swap(std::nullptr_t) { clear(); }
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void swap(PackedAlignedPtr& other)
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{
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m_storage.swap(other.m_storage);
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}
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template<typename Other, typename = std::enable_if_t<Other::isPackedType>>
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void swap(Other& other)
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{
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T* t1 = get();
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T* t2 = other.get();
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set(t2);
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other.set(t1);
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}
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void swap(T* t2)
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{
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T* t1 = get();
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std::swap(t1, t2);
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set(t1);
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}
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private:
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std::array<uint8_t, storageSize> m_storage;
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};
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template<typename T>
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class Packed<T*> : public PackedAlignedPtr<T, 1> {
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public:
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using Base = PackedAlignedPtr<T, 1>;
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using Base::Base;
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// Hash table deleted values, which are only constructed and never copied or destroyed.
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Packed(HashTableDeletedValueType) : Base(bitwise_cast<T*>(static_cast<uintptr_t>(Base::alignment))) { }
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bool isHashTableDeletedValue() const { return Base::get() == bitwise_cast<T*>(static_cast<uintptr_t>(Base::alignment)); }
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};
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template<typename T>
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using PackedPtr = Packed<T*>;
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template <typename T>
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struct GetPtrHelper<PackedPtr<T>> {
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using PtrType = T*;
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static T* getPtr(const PackedPtr<T>& p) { return const_cast<T*>(p.get()); }
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};
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template <typename T>
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struct IsSmartPtr<PackedPtr<T>> {
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static constexpr bool value = true;
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};
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template<typename T>
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struct PackedPtrTraits {
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template<typename U> using RebindTraits = PackedPtrTraits<U>;
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using StorageType = PackedPtr<T>;
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template<class U> static ALWAYS_INLINE T* exchange(StorageType& ptr, U&& newValue) { return ptr.exchange(newValue); }
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template<typename Other> static ALWAYS_INLINE void swap(PackedPtr<T>& a, Other& b) { a.swap(b); }
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static ALWAYS_INLINE T* unwrap(const StorageType& ptr) { return ptr.get(); }
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// We assume that,
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// 1. The alignment is < 4KB. (It is tested by HashTraits).
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// 2. The first page (including nullptr) is never mapped.
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static StorageType hashTableDeletedValue() { return StorageType { bitwise_cast<T*>(static_cast<uintptr_t>(StorageType::alignment)) }; }
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static ALWAYS_INLINE bool isHashTableDeletedValue(const StorageType& ptr) { return ptr.get() == bitwise_cast<T*>(static_cast<uintptr_t>(StorageType::alignment)); }
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};
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template<typename P> struct DefaultHash<PackedPtr<P>> : PtrHash<PackedPtr<P>> { };
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} // namespace WTF
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using WTF::Packed;
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using WTF::PackedAlignedPtr;
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using WTF::PackedPtr;
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