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/*
* Copyright (C) 2024-2025 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. ``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
* 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.
*/
#pragma once
#include <bit>
#include <concepts>
namespace WTF {
template<typename Trait, typename T>
concept TaggingTraits = requires (const T* ptr, typename Trait::StorageType storage, typename Trait::TagType tag) {
{ Trait::defaultTag } -> std::convertible_to<typename Trait::TagType>;
{ Trait::wrap(ptr, tag) } -> std::convertible_to<typename Trait::StorageType>;
{ Trait::unwrapPtr(storage) } -> std::convertible_to<T*>;
{ Trait::unwrapTag(storage) } -> std::convertible_to<typename Trait::TagType>;
};
template<typename T, TaggingTraits<T> Traits>
class TaggedPtr {
WTF_MAKE_FAST_ALLOCATED;
public:
using StorageType = typename Traits::StorageType;
using TagType = typename Traits::TagType;
TaggedPtr() = default;
TaggedPtr(const T* ptr, TagType tag = Traits::defaultTag)
: m_ptr(Traits::wrap(ptr, tag))
{ }
TagType tag() const { return Traits::unwrapTag(m_ptr); }
const T* ptr() const { return Traits::unwrapPtr(m_ptr); }
T* ptr() { return Traits::unwrapPtr(m_ptr); }
void set(const T* t, TagType tag) { m_ptr = Traits::wrap(t, tag); }
void setTag(TagType tag) { m_ptr = Traits::wrap(ptr(), tag); }
TaggedPtr& operator=(const T* t)
{
m_ptr = Traits::wrap(t, tag());
return *this;
}
const T* operator->() const { return ptr(); }
T* operator->() { return ptr(); }
private:
StorageType m_ptr { Traits::wrap(nullptr, Traits::defaultTag) };
};
template<typename T, typename Enum, Enum defaultEnumTag = static_cast<Enum>(0)>
struct EnumTaggingTraits {
using StorageType = uintptr_t;
using TagType = Enum;
static constexpr TagType defaultTag = defaultEnumTag;
static StorageType wrap(const T* ptr, TagType tag)
{
ASSERT_WITH_MESSAGE((static_cast<StorageType>(tag) | tagMask32Bit) == tagMask32Bit, "Tag is too big for 32-bit storage");
ASSERT(fromStorage(toStorage(tag)) == tag);
return std::bit_cast<StorageType>(ptr) | toStorage(tag);
}
#if CPU(ADDRESS64)
static T* unwrapPtr(StorageType storage) { return std::bit_cast<T*>(storage & ptrMask); }
#else
static T* unwrapPtr(StorageType storage) { return std::bit_cast<T*>(storage & ~tagMask32Bit); }
#endif
static TagType unwrapTag(StorageType storage) { return fromStorage(storage); }
static constexpr StorageType tagMask32Bit = (1 << (alignof(std::remove_pointer_t<T>) - 1)) - 1;
#if CPU(ADDRESS64)
static constexpr unsigned tagShift = sizeof(StorageType) * CHAR_BIT - CHAR_BIT + 4; // Save the bottom four bits of the high byte for other uses.
static constexpr StorageType ptrMask = (1ull << tagShift) - 1;
static StorageType toStorage(TagType tag) { return static_cast<StorageType>(tag) << tagShift; }
static TagType fromStorage(StorageType storage) { return static_cast<TagType>(storage >> tagShift); }
#else
static StorageType toStorage(TagType tag) { return static_cast<StorageType>(tag); }
static TagType fromStorage(StorageType storage) { return static_cast<TagType>(storage & tagMask32Bit); }
#endif
};
// Useful for places where you sometimes want to tag and sometimes not based on template parameters.
template<typename T>
struct NoTaggingTraits {
using StorageType = uintptr_t;
using TagType = unsigned;
static constexpr TagType defaultTag = 0;
static StorageType wrap(const T* ptr, TagType) { return std::bit_cast<StorageType>(ptr); }
static T* unwrapPtr(StorageType storage) { return std::bit_cast<T*>(storage); }
static TagType unwrapTag(StorageType) { return defaultTag; }
};
} // namespace WTF
using WTF::TaggedPtr;
using WTF::EnumTaggingTraits;
using WTF::NoTaggingTraits;
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