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Merge pull request #4426 from wwylele/signed-bitfield
Common/Bitfield: store value as unsigned type
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commit
ecc1c575d5
@ -111,15 +111,15 @@
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template <std::size_t Position, std::size_t Bits, typename T>
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template <std::size_t Position, std::size_t Bits, typename T>
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struct BitField {
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struct BitField {
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private:
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private:
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// StorageType is T for non-enum types and the underlying type of T if
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// UnderlyingType is T for non-enum types and the underlying type of T if
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// T is an enumeration. Note that T is wrapped within an enable_if in the
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// T is an enumeration. Note that T is wrapped within an enable_if in the
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// former case to workaround compile errors which arise when using
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// former case to workaround compile errors which arise when using
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// std::underlying_type<T>::type directly.
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// std::underlying_type<T>::type directly.
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using StorageType = typename std::conditional_t<std::is_enum<T>::value, std::underlying_type<T>,
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using UnderlyingType = typename std::conditional_t<std::is_enum_v<T>, std::underlying_type<T>,
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std::enable_if<true, T>>::type;
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std::enable_if<true, T>>::type;
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// Unsigned version of StorageType
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// We store the value as the unsigned type to avoid undefined behaviour on value shifting
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using StorageTypeU = std::make_unsigned_t<StorageType>;
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using StorageType = std::make_unsigned_t<UnderlyingType>;
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public:
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public:
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BitField& operator=(const BitField&) = default;
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BitField& operator=(const BitField&) = default;
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@ -127,7 +127,7 @@ public:
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/// Constants to allow limited introspection of fields if needed
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/// Constants to allow limited introspection of fields if needed
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static constexpr std::size_t position = Position;
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static constexpr std::size_t position = Position;
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static constexpr std::size_t bits = Bits;
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static constexpr std::size_t bits = Bits;
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static constexpr StorageType mask = (((StorageTypeU)~0) >> (8 * sizeof(T) - bits)) << position;
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static constexpr StorageType mask = (((StorageType)~0) >> (8 * sizeof(T) - bits)) << position;
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/**
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/**
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* Formats a value by masking and shifting it according to the field parameters. A value
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* Formats a value by masking and shifting it according to the field parameters. A value
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@ -144,11 +144,12 @@ public:
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* union in a constexpr context.
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* union in a constexpr context.
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*/
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*/
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static constexpr FORCE_INLINE T ExtractValue(const StorageType& storage) {
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static constexpr FORCE_INLINE T ExtractValue(const StorageType& storage) {
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if (std::numeric_limits<T>::is_signed) {
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if constexpr (std::numeric_limits<UnderlyingType>::is_signed) {
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std::size_t shift = 8 * sizeof(T) - bits;
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std::size_t shift = 8 * sizeof(T) - bits;
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return (T)((storage << (shift - position)) >> shift);
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return static_cast<T>(static_cast<UnderlyingType>(storage << (shift - position)) >>
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shift);
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} else {
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} else {
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return (T)((storage & mask) >> position);
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return static_cast<T>((storage & mask) >> position);
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}
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}
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}
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}
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