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/*
* Copyright (C) 2018 Yusuke Suzuki <utatane.tea@gmail.com>.
*
* 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 <wtf/StdLibExtras.h>
namespace WTF {
// The goal of this class is folding a pointer and 1 byte 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.
// In 64bit, we use the upper 5 bits and lower 3 bits (zero due to alignment) since these bits are safe to use even
// with 5-level page tables where the effective pointer width is 57bits.
template<typename PointerType, typename Type>
class CompactPointerTuple {
public:
static_assert(sizeof(Type) == 1, "");
static_assert(std::is_pointer<PointerType>::value, "");
static_assert(alignof(typename std::remove_pointer<PointerType>::type) >= alignof(void*), "");
static_assert(std::is_integral<Type>::value || std::is_enum<Type>::value, "");
CompactPointerTuple() = default;
#if CPU(ADDRESS64)
public:
static constexpr uint64_t encodeType(uint8_t type)
{
// Encode 8bit type UUUDDDDD into 64bit data DDDDD..56bit..UUU.
return (static_cast<uint64_t>(type) << 59) | (static_cast<uint64_t>(type) >> 5);
}
static constexpr uint8_t decodeType(uint64_t value)
{
// Decode 64bit data DDDDD..56bit..UUU into 8bit type UUUDDDDD.
return static_cast<uint8_t>((value >> 59) | (value << 5));
}
static constexpr uint64_t typeMask = encodeType(UINT8_MAX);
static_assert(0xF800000000000007ULL == typeMask, "");
static constexpr uint64_t pointerMask = ~typeMask;
CompactPointerTuple(PointerType pointer, Type type)
: m_data(bitwise_cast<uint64_t>(pointer) | encodeType(static_cast<uint8_t>(type)))
{
ASSERT((bitwise_cast<uint64_t>(pointer) & 0b111) == 0x0);
}
PointerType pointer() const { return bitwise_cast<PointerType>(m_data & pointerMask); }
void setPointer(PointerType pointer)
{
ASSERT((bitwise_cast<uint64_t>(pointer) & 0b111) == 0x0);
m_data = CompactPointerTuple(pointer, type()).m_data;
}
Type type() const { return static_cast<Type>(decodeType(m_data)); }
void setType(Type type)
{
m_data = CompactPointerTuple(pointer(), type).m_data;
}
private:
uint64_t m_data { 0 };
#else
public:
CompactPointerTuple(PointerType pointer, Type type)
: m_pointer(pointer)
, m_type(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
};
} // namespace WTF
using WTF::CompactPointerTuple;