240 lines
6.7 KiB
C++
240 lines
6.7 KiB
C++
/*
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* Copyright (C) 2019-2021 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 "Algorithm.h"
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#include "StdLibExtras.h"
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#include <array>
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#if BOS(DARWIN)
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#include <mach/vm_param.h>
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#endif
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namespace bmalloc {
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template<typename T>
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class Packed {
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public:
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static_assert(std::is_trivial<T>::value);
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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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memcpy(m_storage.data(), &value, sizeof(T));
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}
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T get() const
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{
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T value { };
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memcpy(&value, m_storage.data(), sizeof(T));
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return value;
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}
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void set(const T& value)
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{
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memcpy(m_storage.data(), &value, sizeof(T));
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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 alignment = alignof(T)>
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class PackedAlignedPtr {
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public:
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static_assert(isPowerOfTwo(alignment), "Alignment needs to be power-of-two");
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static constexpr bool isPackedType = true;
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static constexpr unsigned alignmentShiftSizeIfProfitable = getLSBSetNonZeroConstexpr(alignment);
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static constexpr unsigned storageSizeWithoutAlignmentShift = roundUpToMultipleOf<8, uintptr_t>(BOS_EFFECTIVE_ADDRESS_WIDTH) / 8;
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static constexpr unsigned storageSizeWithAlignmentShift = roundUpToMultipleOf<8, uintptr_t>(BOS_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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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 BCPU(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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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 BCPU(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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}
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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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};
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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 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 T* exchange(StorageType& ptr, U&& newValue) { return ptr.exchange(newValue); }
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template<typename Other> static void swap(PackedPtr<T>& a, Other& b) { a.swap(b); }
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static T* unwrap(const StorageType& ptr) { return ptr.get(); }
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};
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} // namespace bmalloc
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