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/*
* Copyright (C) 2018 Yusuke Suzuki <utatane.tea@gmail.com>.
* Copyright (C) 2020 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 <type_traits>
#include <utility>
#include <wtf/FastMalloc.h>
#include <wtf/MathExtras.h>
#include <wtf/StdLibExtras.h>
#if OS(DARWIN)
#include <mach/vm_param.h>
#endif
namespace WTF {
// The goal of this class is folding a pointer and 2 bytes value into 8 bytes in both 32bit and 64bit architectures.
// 32bit architecture just has a pair of byte and pointer, which should be 8 bytes.
// We are assuming 48bit pointers here, which is also assumed in JSValue anyway.
template<typename PointerType, typename Type>
class CompactPointerTuple final {
WTF_MAKE_FAST_ALLOCATED;
public:
static_assert(sizeof(Type) <= 2);
static_assert(std::is_pointer<PointerType>::value);
static_assert(::allowCompactPointers<PointerType>());
static_assert(std::is_integral<Type>::value || std::is_enum<Type>::value);
using UnsignedType = std::make_unsigned_t<std::conditional_t<std::is_same_v<Type, bool>, uint8_t, Type>>;
static_assert(sizeof(UnsignedType) == sizeof(Type));
CompactPointerTuple() = default;
friend bool operator==(const CompactPointerTuple&, const CompactPointerTuple&) = default;
#if CPU(ADDRESS64)
public:
static constexpr unsigned maxNumberOfBitsInPointer = 48;
static_assert(OS_CONSTANT(EFFECTIVE_ADDRESS_WIDTH) <= maxNumberOfBitsInPointer);
#if CPU(LITTLE_ENDIAN)
static constexpr ptrdiff_t offsetOfType()
{
return maxNumberOfBitsInPointer / 8;
}
#endif
static constexpr uint64_t pointerMask = (1ULL << maxNumberOfBitsInPointer) - 1;
CompactPointerTuple(PointerType pointer, Type type)
: m_data(encode(pointer, type))
{
ASSERT(this->type() == type);
ASSERT(this->pointer() == pointer);
}
template<typename OtherPointerType, typename = std::enable_if<std::is_pointer<PointerType>::value && std::is_convertible<OtherPointerType, PointerType>::value>>
CompactPointerTuple(CompactPointerTuple<OtherPointerType, Type>&& other)
: m_data { std::exchange(other.m_data, { }) }
{
}
PointerType pointer() const { return std::bit_cast<PointerType>(m_data & pointerMask); }
void setPointer(PointerType pointer)
{
m_data = encode(pointer, type());
ASSERT(this->pointer() == pointer);
}
Type type() const { return decodeType(m_data); }
void setType(Type type)
{
m_data = encode(pointer(), type);
ASSERT(this->type() == type);
}
uint64_t data() const { return m_data; }
private:
static constexpr uint64_t encodeType(Type type)
{
return static_cast<uint64_t>(static_cast<UnsignedType>(type)) << maxNumberOfBitsInPointer;
}
static constexpr Type decodeType(uint64_t value)
{
return static_cast<Type>(static_cast<UnsignedType>(value >> maxNumberOfBitsInPointer));
}
static uint64_t encode(PointerType pointer, Type type)
{
return std::bit_cast<uint64_t>(pointer) | encodeType(type);
}
uint64_t m_data { 0 };
#else
public:
CompactPointerTuple(PointerType pointer, Type type)
: m_pointer(pointer)
, m_type(type)
{
}
template<typename OtherPointerType, typename = std::enable_if<std::is_pointer<PointerType>::value && std::is_convertible<OtherPointerType, PointerType>::value>>
CompactPointerTuple(CompactPointerTuple<OtherPointerType, Type>&& other)
: m_pointer { std::exchange(other.m_pointer, { }) }
, m_type { std::exchange(other.m_type, { }) }
{
}
PointerType pointer() const { return m_pointer; }
void setPointer(PointerType pointer) { m_pointer = pointer; }
Type type() const { return m_type; }
void setType(Type type) { m_type = type; }
private:
PointerType m_pointer { nullptr };
Type m_type { 0 };
#endif
template<typename, typename> friend class CompactPointerTuple;
};
} // namespace WTF
using WTF::CompactPointerTuple;
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