dolphin/Source/Core/Common/BitUtils.h

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// Copyright 2017 Dolphin Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later
#pragma once
#include <array>
#include <climits>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <initializer_list>
#include <type_traits>
namespace Common
{
///
/// Retrieves the size of a type in bits.
///
/// @tparam T Type to get the size of.
///
/// @return the size of the type in bits.
///
template <typename T>
constexpr size_t BitSize() noexcept
{
return sizeof(T) * CHAR_BIT;
}
///
/// Extracts a bit from a value.
///
/// @param src The value to extract a bit from.
/// @param bit The bit to extract.
///
/// @tparam T The type of the value.
///
/// @return The extracted bit.
///
template <typename T>
constexpr T ExtractBit(const T src, const size_t bit) noexcept
{
return (src >> bit) & static_cast<T>(1);
}
///
/// Extracts a bit from a value.
///
/// @param src The value to extract a bit from.
///
/// @tparam bit The bit to extract.
/// @tparam T The type of the value.
///
/// @return The extracted bit.
///
template <size_t bit, typename T>
constexpr T ExtractBit(const T src) noexcept
{
static_assert(bit < BitSize<T>(), "Specified bit must be within T's bit width.");
return ExtractBit(src, bit);
}
///
/// Extracts a range of bits from a value.
///
/// @param src The value to extract the bits from.
/// @param begin The beginning of the bit range. This is inclusive.
/// @param end The ending of the bit range. This is inclusive.
///
/// @tparam T The type of the value.
/// @tparam Result The returned result type. This is the unsigned analog
/// of a signed type if a signed type is passed as T.
///
/// @return The extracted bits.
///
template <typename T, typename Result = std::make_unsigned_t<T>>
constexpr Result ExtractBits(const T src, const size_t begin, const size_t end) noexcept
{
return static_cast<Result>(((static_cast<Result>(src) << ((BitSize<T>() - 1) - end)) >>
(BitSize<T>() - end + begin - 1)));
}
///
/// Extracts a range of bits from a value.
///
/// @param src The value to extract the bits from.
///
/// @tparam begin The beginning of the bit range. This is inclusive.
/// @tparam end The ending of the bit range. This is inclusive.
/// @tparam T The type of the value.
/// @tparam Result The returned result type. This is the unsigned analog
/// of a signed type if a signed type is passed as T.
///
/// @return The extracted bits.
///
template <size_t begin, size_t end, typename T, typename Result = std::make_unsigned_t<T>>
constexpr Result ExtractBits(const T src) noexcept
{
static_assert(begin < end, "Beginning bit must be less than the ending bit.");
static_assert(begin < BitSize<T>(), "Beginning bit is larger than T's bit width.");
static_assert(end < BitSize<T>(), "Ending bit is larger than T's bit width.");
return ExtractBits<T, Result>(src, begin, end);
}
///
/// Verifies whether the supplied value is a valid bit mask of the form 0b00...0011...11.
/// Both edge cases of all zeros and all ones are considered valid masks, too.
///
/// @param mask The mask value to test for validity.
///
/// @tparam T The type of the value.
///
/// @return A bool indicating whether the mask is valid.
///
template <typename T>
constexpr bool IsValidLowMask(const T mask) noexcept
{
static_assert(std::is_integral<T>::value, "Mask must be an integral type.");
static_assert(std::is_unsigned<T>::value, "Signed masks can introduce hard to find bugs.");
// Can be efficiently determined without looping or bit counting. It's the counterpart
// to https://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2
// and doesn't require special casing either edge case.
return (mask & (mask + 1)) == 0;
}
///
/// Reinterpret objects of one type as another by bit-casting between object representations.
///
/// @remark This is the example implementation of std::bit_cast which is to be included
/// in C++2a. See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0476r2.html
/// for more details. The only difference is this variant is not constexpr,
/// as the mechanism for bit_cast requires a compiler built-in to have that quality.
///
/// @param source The source object to convert to another representation.
///
/// @tparam To The type to reinterpret source as.
/// @tparam From The initial type representation of source.
///
/// @return The representation of type From as type To.
///
/// @pre Both To and From types must be the same size
/// @pre Both To and From types must satisfy the TriviallyCopyable concept.
///
template <typename To, typename From>
inline To BitCast(const From& source) noexcept
{
static_assert(sizeof(From) == sizeof(To),
"BitCast source and destination types must be equal in size.");
static_assert(std::is_trivially_copyable<From>(),
"BitCast source type must be trivially copyable.");
static_assert(std::is_trivially_copyable<To>(),
"BitCast destination type must be trivially copyable.");
alignas(To) std::byte storage[sizeof(To)];
std::memcpy(&storage, &source, sizeof(storage));
return reinterpret_cast<To&>(storage);
}
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template <typename T, typename PtrType>
class BitCastPtrType
{
public:
static_assert(std::is_trivially_copyable<PtrType>(),
"BitCastPtr source type must be trivially copyable.");
static_assert(std::is_trivially_copyable<T>(),
"BitCastPtr destination type must be trivially copyable.");
explicit BitCastPtrType(PtrType* ptr) : m_ptr(ptr) {}
// Enable operator= only for pointers to non-const data
template <typename S>
inline typename std::enable_if<std::is_same<S, T>() && !std::is_const<PtrType>()>::type
operator=(const S& source)
{
std::memcpy(m_ptr, &source, sizeof(source));
}
inline operator T() const
{
T result;
std::memcpy(&result, m_ptr, sizeof(result));
return result;
}
private:
PtrType* m_ptr;
};
// Provides an aliasing-safe alternative to reinterpret_cast'ing pointers to structs
// Conversion constructor and operator= provided for a convenient syntax.
// Usage: MyStruct s = BitCastPtr<MyStruct>(some_ptr);
// BitCastPtr<MyStruct>(some_ptr) = s;
template <typename T, typename PtrType>
inline auto BitCastPtr(PtrType* ptr) noexcept -> BitCastPtrType<T, PtrType>
{
return BitCastPtrType<T, PtrType>{ptr};
}
// Similar to BitCastPtr, but specifically for aliasing structs to arrays.
template <typename ArrayType, typename T,
typename Container = std::array<ArrayType, sizeof(T) / sizeof(ArrayType)>>
inline auto BitCastToArray(const T& obj) noexcept -> Container
{
static_assert(sizeof(T) % sizeof(ArrayType) == 0,
"Size of array type must be a factor of size of source type.");
static_assert(std::is_trivially_copyable<T>(),
"BitCastToArray source type must be trivially copyable.");
static_assert(std::is_trivially_copyable<Container>(),
"BitCastToArray array type must be trivially copyable.");
Container result;
std::memcpy(result.data(), &obj, sizeof(T));
return result;
}
template <typename ArrayType, typename T,
typename Container = std::array<ArrayType, sizeof(T) / sizeof(ArrayType)>>
inline void BitCastFromArray(const Container& array, T& obj) noexcept
{
static_assert(sizeof(T) % sizeof(ArrayType) == 0,
"Size of array type must be a factor of size of destination type.");
static_assert(std::is_trivially_copyable<Container>(),
"BitCastFromArray array type must be trivially copyable.");
static_assert(std::is_trivially_copyable<T>(),
"BitCastFromArray destination type must be trivially copyable.");
std::memcpy(&obj, array.data(), sizeof(T));
}
template <typename ArrayType, typename T,
typename Container = std::array<ArrayType, sizeof(T) / sizeof(ArrayType)>>
inline auto BitCastFromArray(const Container& array) noexcept -> T
{
static_assert(sizeof(T) % sizeof(ArrayType) == 0,
"Size of array type must be a factor of size of destination type.");
static_assert(std::is_trivially_copyable<Container>(),
"BitCastFromArray array type must be trivially copyable.");
static_assert(std::is_trivially_copyable<T>(),
"BitCastFromArray destination type must be trivially copyable.");
T obj;
std::memcpy(&obj, array.data(), sizeof(T));
return obj;
}
template <typename T>
void SetBit(T& value, size_t bit_number, bool bit_value)
{
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static_assert(std::is_unsigned<T>(), "SetBit is only sane on unsigned types.");
if (bit_value)
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value |= (T{1} << bit_number);
else
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value &= ~(T{1} << bit_number);
}
template <size_t bit_number, typename T>
void SetBit(T& value, bool bit_value)
{
SetBit(value, bit_number, bit_value);
}
template <typename T>
class FlagBit
{
public:
FlagBit(std::underlying_type_t<T>& bits, T bit) : m_bits(bits), m_bit(bit) {}
explicit operator bool() const
{
return (m_bits & static_cast<std::underlying_type_t<T>>(m_bit)) != 0;
}
FlagBit& operator=(const bool rhs)
{
if (rhs)
m_bits |= static_cast<std::underlying_type_t<T>>(m_bit);
else
m_bits &= ~static_cast<std::underlying_type_t<T>>(m_bit);
return *this;
}
private:
std::underlying_type_t<T>& m_bits;
T m_bit;
};
template <typename T>
class Flags
{
public:
constexpr Flags() = default;
constexpr Flags(std::initializer_list<T> bits)
{
for (auto bit : bits)
{
m_hex |= static_cast<std::underlying_type_t<T>>(bit);
}
}
FlagBit<T> operator[](T bit) { return FlagBit(m_hex, bit); }
std::underlying_type_t<T> m_hex = 0;
};
// Left-shift a value and set new LSBs to that of the supplied LSB.
// Converts a value from a N-bit range to an (N+X)-bit range. e.g. 0x101 -> 0x10111
template <typename T>
T ExpandValue(T value, size_t left_shift_amount)
{
static_assert(std::is_unsigned<T>(), "ExpandValue is only sane on unsigned types.");
return (value << left_shift_amount) |
(T(-ExtractBit<0>(value)) >> (BitSize<T>() - left_shift_amount));
}
} // namespace Common