dolphin/Source/Core/Common/BitField.h

508 lines
19 KiB
C++

// Copyright 2014 Dolphin Emulator Project
// Licensed under GPLv2+
// Refer to the license.txt file included.
// Copyright 2014 Tony Wasserka
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * 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.
// * Neither the name of the owner nor the names of its contributors may
// be used to endorse or promote products derived from this software
// without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "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 THE COPYRIGHT
// OWNER 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 <cstddef>
#include <fmt/format.h>
#include <iterator>
#include <limits>
#include <type_traits>
#include "Common/Inline.h"
/*
* Abstract bitfield class
*
* Allows endianness-independent access to individual bitfields within some raw
* integer value. The assembly generated by this class is identical to the
* usage of raw bitfields, so it's a perfectly fine replacement.
*
* For BitField<X,Y,Z>, X is the distance of the bitfield to the LSB of the
* raw value, Y is the length in bits of the bitfield. Z is an integer type
* which determines the sign of the bitfield. Z must have the same size as the
* raw integer.
*
*
* General usage:
*
* Create a new union with the raw integer value as a member.
* Then for each bitfield you want to expose, add a BitField member
* in the union. The template parameters are the bit offset and the number
* of desired bits.
*
* Changes in the bitfield members will then get reflected in the raw integer
* value and vice-versa.
*
*
* Sample usage:
*
* union SomeRegister
* {
* u32 hex;
*
* BitField<0,7,u32> first_seven_bits; // unsigned
* BitField<7,8,u32> next_eight_bits; // unsigned
* BitField<3,15,s32> some_signed_fields; // signed
* };
*
* This is equivalent to the little-endian specific code:
*
* union SomeRegister
* {
* u32 hex;
*
* struct
* {
* u32 first_seven_bits : 7;
* u32 next_eight_bits : 8;
* };
* struct
* {
* u32 : 3; // padding
* s32 some_signed_fields : 15;
* };
* };
*
*
* Caveats:
*
* 1)
* BitField provides automatic casting from and to the storage type where
* appropriate. However, when using non-typesafe functions like printf, an
* explicit cast must be performed on the BitField object to make sure it gets
* passed correctly, e.g.:
* printf("Value: %d", (s32)some_register.some_signed_fields);
* Note that this does not apply when using fmt, as a formatter is provided that
* handles this conversion automatically.
*
* 2)
* Not really a caveat, but potentially irritating: This class is used in some
* packed structures that do not guarantee proper alignment. Therefore we have
* to use #pragma pack here not to pack the members of the class, but instead
* to break GCC's assumption that the members of the class are aligned on
* sizeof(StorageType).
* TODO(neobrain): Confirm that this is a proper fix and not just masking
* symptoms.
*/
#pragma pack(1)
template <std::size_t position, std::size_t bits, typename T,
// StorageType is T for non-enum types and the underlying type of T if
// T is an enumeration. Note that T is wrapped within an enable_if in the
// former case to workaround compile errors which arise when using
// std::underlying_type<T>::type directly.
typename StorageType = typename std::conditional_t<
std::is_enum<T>::value, std::underlying_type<T>, std::enable_if<true, T>>::type>
struct BitField
{
private:
// This constructor might be considered ambiguous:
// Would it initialize the storage or just the bitfield?
// Hence, delete it. Use the assignment operator to set bitfield values!
BitField(T val) = delete;
public:
// Force default constructor to be created
// so that we can use this within unions
constexpr BitField() = default;
// Visual Studio (as of VS2017) considers BitField to not be trivially
// copyable if we delete this copy assignment operator.
// https://developercommunity.visualstudio.com/content/problem/101208/c-compiler-is-overly-strict-regarding-whether-a-cl.html
#ifndef _MSC_VER
// We explicitly delete the copy assignment operator here, because the
// default copy assignment would copy the full storage value, rather than
// just the bits relevant to this particular bit field.
// Ideally, we would just implement the copy assignment to copy only the
// relevant bits, but we're prevented from doing that because the savestate
// code expects that this class is trivially copyable.
BitField& operator=(const BitField&) = delete;
#endif
DOLPHIN_FORCE_INLINE BitField& operator=(T val)
{
storage = (storage & ~GetMask()) | ((static_cast<StorageType>(val) << position) & GetMask());
return *this;
}
constexpr T Value() const { return Value(std::is_signed<T>()); }
constexpr operator T() const { return Value(); }
constexpr std::size_t StartBit() const { return position; }
constexpr std::size_t NumBits() const { return bits; }
private:
// Unsigned version of StorageType
using StorageTypeU = std::make_unsigned_t<StorageType>;
constexpr T Value(std::true_type) const
{
const size_t shift_amount = 8 * sizeof(StorageType) - bits;
return static_cast<T>((storage << (shift_amount - position)) >> shift_amount);
}
constexpr T Value(std::false_type) const
{
return static_cast<T>((storage & GetMask()) >> position);
}
static constexpr StorageType GetMask()
{
return (std::numeric_limits<StorageTypeU>::max() >> (8 * sizeof(StorageType) - bits))
<< position;
}
StorageType storage;
static_assert(bits + position <= 8 * sizeof(StorageType), "Bitfield out of range");
static_assert(sizeof(T) <= sizeof(StorageType), "T must fit in StorageType");
// And, you know, just in case people specify something stupid like bits=position=0x80000000
static_assert(position < 8 * sizeof(StorageType), "Invalid position");
static_assert(bits <= 8 * sizeof(T), "Invalid number of bits");
static_assert(bits > 0, "Invalid number of bits");
};
#pragma pack()
// Use the underlying type's formatter for BitFields, if one exists
template <std::size_t position, std::size_t bits, typename T, typename S>
struct fmt::formatter<BitField<position, bits, T, S>>
{
fmt::formatter<T> m_formatter;
constexpr auto parse(format_parse_context& ctx) { return m_formatter.parse(ctx); }
template <typename FormatContext>
auto format(const BitField<position, bits, T, S>& bitfield, FormatContext& ctx)
{
return m_formatter.format(bitfield.Value(), ctx);
}
};
// Language limitations require the following to make these formattable
// (formatter<BitFieldArray<position, bits, size, T>::Ref> is not legal)
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
class BitFieldArrayConstRef;
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
class BitFieldArrayRef;
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
class BitFieldArrayConstIterator;
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
class BitFieldArrayIterator;
#pragma pack(1)
template <std::size_t position, std::size_t bits, std::size_t size, typename T,
// StorageType is T for non-enum types and the underlying type of T if
// T is an enumeration. Note that T is wrapped within an enable_if in the
// former case to workaround compile errors which arise when using
// std::underlying_type<T>::type directly.
typename StorageType = typename std::conditional_t<
std::is_enum<T>::value, std::underlying_type<T>, std::enable_if<true, T>>::type>
struct BitFieldArray
{
using Ref = BitFieldArrayRef<position, bits, size, T, StorageType>;
using ConstRef = BitFieldArrayConstRef<position, bits, size, T, StorageType>;
using Iterator = BitFieldArrayIterator<position, bits, size, T, StorageType>;
using ConstIterator = BitFieldArrayConstIterator<position, bits, size, T, StorageType>;
private:
// This constructor might be considered ambiguous:
// Would it initialize the storage or just the bitfield?
// Hence, delete it. Use the assignment operator to set bitfield values!
BitFieldArray(T val) = delete;
public:
// Force default constructor to be created
// so that we can use this within unions
constexpr BitFieldArray() = default;
// Visual Studio (as of VS2017) considers BitField to not be trivially
// copyable if we delete this copy assignment operator.
// https://developercommunity.visualstudio.com/content/problem/101208/c-compiler-is-overly-strict-regarding-whether-a-cl.html
#ifndef _MSC_VER
// We explicitly delete the copy assignment operator here, because the
// default copy assignment would copy the full storage value, rather than
// just the bits relevant to this particular bit field.
// Ideally, we would just implement the copy assignment to copy only the
// relevant bits, but we're prevented from doing that because the savestate
// code expects that this class is trivially copyable.
BitFieldArray& operator=(const BitFieldArray&) = delete;
#endif
public:
constexpr std::size_t StartBit() const { return position; }
constexpr std::size_t NumBits() const { return bits; }
constexpr std::size_t Size() const { return size; }
constexpr std::size_t TotalNumBits() const { return bits * size; }
constexpr T Value(size_t index) const { return Value(std::is_signed<T>(), index); }
void SetValue(size_t index, T value)
{
const size_t pos = position + bits * index;
storage = (storage & ~GetElementMask(index)) |
((static_cast<StorageType>(value) << pos) & GetElementMask(index));
}
Ref operator[](size_t index) { return Ref(this, index); }
constexpr const ConstRef operator[](size_t index) const { return ConstRef(this, index); }
constexpr Iterator begin() { return Iterator(this, 0); }
constexpr Iterator end() { return Iterator(this, size); }
constexpr ConstIterator begin() const { return ConstIterator(this, 0); }
constexpr ConstIterator end() const { return ConstIterator(this, size); }
constexpr ConstIterator cbegin() const { return begin(); }
constexpr ConstIterator cend() const { return end(); }
private:
// Unsigned version of StorageType
using StorageTypeU = std::make_unsigned_t<StorageType>;
constexpr T Value(std::true_type, size_t index) const
{
const size_t pos = position + bits * index;
const size_t shift_amount = 8 * sizeof(StorageType) - bits;
return static_cast<T>((storage << (shift_amount - pos)) >> shift_amount);
}
constexpr T Value(std::false_type, size_t index) const
{
const size_t pos = position + bits * index;
return static_cast<T>((storage & GetElementMask(index)) >> pos);
}
static constexpr StorageType GetElementMask(size_t index)
{
const size_t pos = position + bits * index;
return (std::numeric_limits<StorageTypeU>::max() >> (8 * sizeof(StorageType) - bits)) << pos;
}
StorageType storage;
static_assert(bits * size + position <= 8 * sizeof(StorageType), "Bitfield array out of range");
static_assert(sizeof(T) <= sizeof(StorageType), "T must fit in StorageType");
// And, you know, just in case people specify something stupid like bits=position=0x80000000
static_assert(position < 8 * sizeof(StorageType), "Invalid position");
static_assert(bits <= 8 * sizeof(T), "Invalid number of bits");
static_assert(bits > 0, "Invalid number of bits");
static_assert(size <= 8 * sizeof(StorageType), "Invalid size");
static_assert(size > 0, "Invalid size");
};
#pragma pack()
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
class BitFieldArrayConstRef
{
friend struct BitFieldArray<position, bits, size, T, S>;
friend class BitFieldArrayConstIterator<position, bits, size, T, S>;
public:
constexpr T Value() const { return m_array->Value(m_index); };
constexpr operator T() const { return Value(); }
private:
constexpr BitFieldArrayConstRef(const BitFieldArray<position, bits, size, T, S>* array,
size_t index)
: m_array(array), m_index(index)
{
}
const BitFieldArray<position, bits, size, T, S>* const m_array;
const size_t m_index;
};
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
class BitFieldArrayRef
{
friend struct BitFieldArray<position, bits, size, T, S>;
friend class BitFieldArrayIterator<position, bits, size, T, S>;
public:
constexpr T Value() const { return m_array->Value(m_index); };
constexpr operator T() const { return Value(); }
T operator=(const BitFieldArrayRef<position, bits, size, T, S>& value) const
{
m_array->SetValue(m_index, value);
return value;
}
T operator=(T value) const
{
m_array->SetValue(m_index, value);
return value;
}
private:
constexpr BitFieldArrayRef(BitFieldArray<position, bits, size, T, S>* array, size_t index)
: m_array(array), m_index(index)
{
}
BitFieldArray<position, bits, size, T, S>* const m_array;
const size_t m_index;
};
// Satisfies LegacyOutputIterator / std::output_iterator.
// Does not satisfy LegacyInputIterator / std::input_iterator as std::output_iterator_tag does not
// extend std::input_iterator_tag.
// Does not satisfy LegacyForwardIterator / std::forward_iterator, as that requires use of real
// references instead of proxy objects.
// This iterator allows use of BitFieldArray in range-based for loops, and with fmt::join.
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
class BitFieldArrayIterator
{
friend struct BitFieldArray<position, bits, size, T, S>;
public:
using iterator_category = std::output_iterator_tag;
using value_type = T;
using difference_type = ptrdiff_t;
using pointer = void;
using reference = BitFieldArrayRef<position, bits, size, T, S>;
private:
constexpr BitFieldArrayIterator(BitFieldArray<position, bits, size, T, S>* array, size_t index)
: m_array(array), m_index(index)
{
}
public:
// Required by std::input_or_output_iterator
constexpr BitFieldArrayIterator() = default;
// Required by LegacyIterator
constexpr BitFieldArrayIterator(const BitFieldArrayIterator& other) = default;
// Required by LegacyIterator
BitFieldArrayIterator& operator=(const BitFieldArrayIterator& other) = default;
// Move constructor and assignment operators, explicitly defined for completeness
constexpr BitFieldArrayIterator(BitFieldArrayIterator&& other) = default;
BitFieldArrayIterator& operator=(BitFieldArrayIterator&& other) = default;
public:
BitFieldArrayIterator& operator++()
{
m_index++;
return *this;
}
BitFieldArrayIterator operator++(int)
{
BitFieldArrayIterator other(*this);
++*this;
return other;
}
constexpr reference operator*() const { return reference(m_array, m_index); }
constexpr bool operator==(BitFieldArrayIterator other) const { return m_index == other.m_index; }
constexpr bool operator!=(BitFieldArrayIterator other) const { return m_index != other.m_index; }
private:
BitFieldArray<position, bits, size, T, S>* m_array;
size_t m_index;
};
// Satisfies LegacyInputIterator / std::input_iterator.
// Does not satisfy LegacyForwardIterator / std::forward_iterator, as that requires use of real
// references instead of proxy objects.
// This iterator allows use of BitFieldArray in range-based for loops, and with fmt::join.
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
class BitFieldArrayConstIterator
{
friend struct BitFieldArray<position, bits, size, T, S>;
public:
using iterator_category = std::input_iterator_tag;
using value_type = T;
using difference_type = ptrdiff_t;
using pointer = void;
using reference = BitFieldArrayConstRef<position, bits, size, T, S>;
private:
constexpr BitFieldArrayConstIterator(const BitFieldArray<position, bits, size, T, S>* array,
size_t index)
: m_array(array), m_index(index)
{
}
public:
// Required by std::input_or_output_iterator
constexpr BitFieldArrayConstIterator() = default;
// Required by LegacyIterator
constexpr BitFieldArrayConstIterator(const BitFieldArrayConstIterator& other) = default;
// Required by LegacyIterator
BitFieldArrayConstIterator& operator=(const BitFieldArrayConstIterator& other) = default;
// Move constructor and assignment operators, explicitly defined for completeness
constexpr BitFieldArrayConstIterator(BitFieldArrayConstIterator&& other) = default;
BitFieldArrayConstIterator& operator=(BitFieldArrayConstIterator&& other) = default;
public:
BitFieldArrayConstIterator& operator++()
{
m_index++;
return *this;
}
BitFieldArrayConstIterator operator++(int)
{
BitFieldArrayConstIterator other(*this);
++*this;
return other;
}
constexpr reference operator*() const { return reference(m_array, m_index); }
constexpr bool operator==(BitFieldArrayConstIterator other) const
{
return m_index == other.m_index;
}
constexpr bool operator!=(BitFieldArrayConstIterator other) const
{
return m_index != other.m_index;
}
private:
const BitFieldArray<position, bits, size, T, S>* m_array;
size_t m_index;
};
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
struct fmt::formatter<BitFieldArrayRef<position, bits, size, T, S>>
{
fmt::formatter<T> m_formatter;
constexpr auto parse(format_parse_context& ctx) { return m_formatter.parse(ctx); }
template <typename FormatContext>
auto format(const BitFieldArrayRef<position, bits, size, T, S>& ref, FormatContext& ctx)
{
return m_formatter.format(ref.Value(), ctx);
}
};
template <std::size_t position, std::size_t bits, std::size_t size, typename T, typename S>
struct fmt::formatter<BitFieldArrayConstRef<position, bits, size, T, S>>
{
fmt::formatter<T> m_formatter;
constexpr auto parse(format_parse_context& ctx) { return m_formatter.parse(ctx); }
template <typename FormatContext>
auto format(const BitFieldArrayConstRef<position, bits, size, T, S>& ref, FormatContext& ctx)
{
return m_formatter.format(ref.Value(), ctx);
}
};