-// The following implements the BitUnion system of defining bitfields
-//on top of an underlying class. This is done through the extensive use of
-//both named and unnamed unions which all contain the same actual storage.
-//Since they're unioned with each other, all of these storage locations
-//overlap. This allows all of the bitfields to manipulate the same data
-//without having to know about each other. More details are provided with the
-//individual components.
-
-//This namespace is for classes which implement the backend of the BitUnion
-//stuff. Don't use any of this directly! Use the macros at the end instead.
-namespace BitfieldBackend
-{
- //A base class for all bitfields. It instantiates the actual storage,
- //and provides getBits and setBits functions for manipulating it. The
- //Data template parameter is type of the underlying storage.
- template<class Data>
- class BitfieldBase
- {
- protected:
- Data __data;
-
- //This function returns a range of bits from the underlying storage.
- //It relies on the "bits" function above. It's the user's
- //responsibility to make sure that there is a properly overloaded
- //version of this function for whatever type they want to overlay.
- inline uint64_t
- getBits(int first, int last)
- {
- return bits(__data, first, last);
- }
-
- //Similar to the above, but for settings bits with replaceBits.
- inline void
- setBits(int first, int last, uint64_t val)
- {
- replaceBits(__data, first, last, val);
- }
- };
-
- //A class which specializes a given base so that it can only be read
- //from. This is accomplished by only passing through the conversion
- //operator.
- template<class Type, class Base>
- class _BitfieldRO : public Base
- {
- public:
- operator const Type ()
- {
- return *((Base *)this);
- }
- };
-
- //Similar to the above, but only allows writing.
- template<class Type, class Base>
- class _BitfieldWO : public Base
- {
- public:
- const Type operator=(const Type & _data)
- {
- *((Base *)this) = _data;
- return _data;
- }
- };
-
- //This class implements ordinary bitfields, that is a span of bits
- //who's msb is "first", and who's lsb is "last".
- template<class Data, int first, int last=first>
- class _Bitfield : public BitfieldBase<Data>
- {
- public:
- operator const Data ()
- {
- return this->getBits(first, last);
- }
-
- const Data
- operator=(const Data & _data)
- {
- this->setBits(first, last, _data);
- return _data;
- }
- };
-
- //When a BitUnion is set up, an underlying class is created which holds
- //the actual union. This class then inherits from it, and provids the
- //implementations for various operators. Setting things up this way
- //prevents having to redefine these functions in every different BitUnion
- //type. More operators could be implemented in the future, as the need
- //arises.
- template <class Type, class Base>
- class BitUnionOperators : public Base
- {
- public:
- operator const Type ()
- {
- return Base::__data;
- }
-
- const Type
- operator=(const Type & _data)
- {
- Base::__data = _data;
- }
-
- bool
- operator<(const Base & base)
- {
- return Base::__data < base.__data;
- }
-
- bool
- operator==(const Base & base)
- {
- return Base::__data == base.__data;
- }
- };
-}
-
-//This macro is a backend for other macros that specialize it slightly.
-//First, it creates/extends a namespace "BitfieldUnderlyingClasses" and
-//sticks the class which has the actual union in it, which
-//BitfieldOperators above inherits from. Putting these classes in a special
-//namespace ensures that there will be no collisions with other names as long
-//as the BitUnion names themselves are all distinct and nothing else uses
-//the BitfieldUnderlyingClasses namespace, which is unlikely. The class itself
-//creates a typedef of the "type" parameter called __DataType. This allows
-//the type to propagate outside of the macro itself in a controlled way.
-//Finally, the base storage is defined which BitfieldOperators will refer to
-//in the operators it defines. This macro is intended to be followed by
-//bitfield definitions which will end up inside it's union. As explained
-//above, these is overlayed the __data member in its entirety by each of the
-//bitfields which are defined in the union, creating shared storage with no
-//overhead.
-#define __BitUnion(type, name) \
- namespace BitfieldUnderlyingClasses \
- { \
- class name; \
- } \
- class BitfieldUnderlyingClasses::name { \
- public: \
- typedef type __DataType; \
- union { \
- type __data;\
-
-//This closes off the class and union started by the above macro. It is
-//followed by a typedef which makes "name" refer to a BitfieldOperator
-//class inheriting from the class and union just defined, which completes
-//building up the type for the user.
-#define EndBitUnion(name) \
- }; \
- }; \
- typedef BitfieldBackend::BitUnionOperators< \
- BitfieldUnderlyingClasses::name::__DataType, \
- BitfieldUnderlyingClasses::name> name;
-
-//This sets up a bitfield which has other bitfields nested inside of it. The
-//__data member functions like the "underlying storage" of the top level
-//BitUnion. Like everything else, it overlays with the top level storage, so
-//making it a regular bitfield type makes the entire thing function as a
-//regular bitfield when referred to by itself. The operators are defined in
-//the macro itself instead of a class for technical reasons. If someone
-//determines a way to move them to one, please do so.
-#define __SubBitUnion(type, name) \
- union { \
- type __data; \
- inline operator const __DataType () \
- { return __data; } \
- \
- inline const __DataType operator = (const __DataType & _data) \
- { __data = _data; }
-
-//This closes off the union created above and gives it a name. Unlike the top
-//level BitUnion, we're interested in creating an object instead of a type.
-#define EndSubBitUnion(name) } name;
-
-//The preprocessor will treat everything inside of parenthesis as a single
-//argument even if it has commas in it. This is used to pass in templated
-//classes which typically have commas to seperate their parameters.
-#define wrap(guts) guts
-
-//Read only bitfields
-//This wraps another bitfield class inside a _BitfieldRO class using
-//inheritance. As explained above, the _BitfieldRO class only passes through
-//the conversion operator, so the underlying bitfield can then only be read
-//from.
-#define __BitfieldRO(base) \
- BitfieldBackend::_BitfieldRO<__DataType, base>
-#define __SubBitUnionRO(name, base) \
- __SubBitUnion(wrap(_BitfieldRO<__DataType, base>), name)
-
-//Write only bitfields
-//Similar to above, but for making write only versions of bitfields with
-//_BitfieldWO.
-#define __BitfieldWO(base) \
- BitfieldBackend::_BitfieldWO<__DataType, base>
-#define __SubBitUnionWO(name, base) \
- __SubBitUnion(wrap(_BitfieldWO<__DataType, base>), name)
-
-//Regular bitfields
-//This uses all of the above to define macros for read/write, read only, and
-//write only versions of regular bitfields.
-#define Bitfield(first, last) \
- BitfieldBackend::_Bitfield<__DataType, first, last>
-#define SubBitUnion(name, first, last) \
- __SubBitUnion(Bitfield(first, last), name)
-#define BitfieldRO(first, last) __BitfieldRO(Bitfield(first, last))
-#define SubBitUnionRO(name, first, last) \
- __SubBitUnionRO(Bitfield(first, last), name)
-#define BitfieldWO(first, last) __BitfieldWO(Bitfield(first, last))
-#define SubBitUnionWO(name, first, last) \
- __SubBitUnionWO(Bitfield(first, last), name)
-
-//Use this to define an arbitrary type overlayed with bitfields.
-#define BitUnion(type, name) __BitUnion(type, name)
-
-//Use this to define conveniently sized values overlayed with bitfields.
-#define BitUnion64(name) __BitUnion(uint64_t, name)
-#define BitUnion32(name) __BitUnion(uint32_t, name)
-#define BitUnion16(name) __BitUnion(uint16_t, name)
-#define BitUnion8(name) __BitUnion(uint8_t, name)
-