}
+
/**
* Extract the bitfield from position 'first' to 'last' (inclusive)
* from 'val' and right justify it. MSB is numbered 63, LSB is 0.
return (val >> last) & mask(nbits);
}
+/**
+ * Mask off the given bits in place like bits() but without shifting.
+ * msb = 63, lsb = 0
+ */
+template <class T>
+inline
+T
+mbits(T val, int first, int last)
+{
+ return val & (mask(first+1) & ~mask(last));
+}
+
+inline uint64_t
+mask(int first, int last)
+{
+ return mbits((uint64_t)-1LL, first, last);
+}
+
/**
* Sign-extend an N-bit value to 64 bits.
*/
val = insertBits(val, first, last, bit_val);
}
+/**
+ * Returns the bit position of the MSB that is set in the input
+ */
+inline
+int
+findMsbSet(uint64_t val) {
+ int msb = 0;
+ if (!val)
+ return 0;
+ if (bits(val, 63,32)) { msb += 32; val >>= 32; }
+ if (bits(val, 31,16)) { msb += 16; val >>= 16; }
+ if (bits(val, 15,8)) { msb += 8; val >>= 8; }
+ if (bits(val, 7,4)) { msb += 4; val >>= 4; }
+ if (bits(val, 3,2)) { msb += 2; val >>= 2; }
+ if (bits(val, 1,1)) { msb += 1; }
+ return msb;
+}
+
+// The following implements the BitUnion system of defining bitfields
+//on top of an underlying class. This is done through the pervasive 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 have access to 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 these directly, except for the Bitfield classes in
+//the *BitfieldTypes class(es).
+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) const
+ {
+ 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);
+ }
+ };
+
+ //This class contains all the "regular" bitfield classes. It is inherited
+ //by all BitUnions which give them access to those types.
+ template<class Type>
+ class RegularBitfieldTypes
+ {
+ protected:
+ //This class implements ordinary bitfields, that is a span of bits
+ //who's msb is "first", and who's lsb is "last".
+ template<int first, int last=first>
+ class Bitfield : public BitfieldBase<Type>
+ {
+ public:
+ operator uint64_t () const
+ {
+ return this->getBits(first, last);
+ }
+
+ uint64_t
+ operator=(const uint64_t _data)
+ {
+ this->setBits(first, last, _data);
+ return _data;
+ }
+ };
+
+ //A class which specializes the above so that it can only be read
+ //from. This is accomplished explicitly making sure the assignment
+ //operator is blocked. The conversion operator is carried through
+ //inheritance. This will unfortunately need to be copied into each
+ //bitfield type due to limitations with how templates work
+ template<int first, int last=first>
+ class BitfieldRO : public Bitfield<first, last>
+ {
+ private:
+ uint64_t
+ operator=(const uint64_t _data);
+ };
+
+ //Similar to the above, but only allows writing.
+ template<int first, int last=first>
+ class BitfieldWO : public Bitfield<first, last>
+ {
+ private:
+ operator uint64_t () const;
+
+ public:
+ using Bitfield<first, last>::operator=;
+ };
+ };
+
+ //This class contains all the "regular" bitfield classes. It is inherited
+ //by all BitUnions which give them access to those types.
+ template<class Type>
+ class SignedBitfieldTypes
+ {
+ protected:
+ //This class implements ordinary bitfields, that is a span of bits
+ //who's msb is "first", and who's lsb is "last".
+ template<int first, int last=first>
+ class SignedBitfield : public BitfieldBase<Type>
+ {
+ public:
+ operator int64_t () const
+ {
+ return sext<first - last + 1>(this->getBits(first, last));
+ }
+
+ int64_t
+ operator=(const int64_t _data)
+ {
+ this->setBits(first, last, _data);
+ return _data;
+ }
+ };
+
+ //A class which specializes the above so that it can only be read
+ //from. This is accomplished explicitly making sure the assignment
+ //operator is blocked. The conversion operator is carried through
+ //inheritance. This will unfortunately need to be copied into each
+ //bitfield type due to limitations with how templates work
+ template<int first, int last=first>
+ class SignedBitfieldRO : public SignedBitfield<first, last>
+ {
+ private:
+ int64_t
+ operator=(const int64_t _data);
+ };
+
+ //Similar to the above, but only allows writing.
+ template<int first, int last=first>
+ class SignedBitfieldWO : public SignedBitfield<first, last>
+ {
+ private:
+ operator int64_t () const;
+
+ public:
+ int64_t operator=(const int64_t _data)
+ {
+ *((SignedBitfield<first, last> *)this) = _data;
+ return _data;
+ }
+ };
+ };
+
+ template<class Type>
+ class BitfieldTypes : public RegularBitfieldTypes<Type>,
+ public SignedBitfieldTypes<Type>
+ {};
+
+ //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 Type () const
+ {
+ return Base::__data;
+ }
+
+ Type
+ operator=(const Type & _data)
+ {
+ Base::__data = _data;
+ return _data;
+ }
+
+ bool
+ operator<(const Base & base) const
+ {
+ return Base::__data < base.__data;
+ }
+
+ bool
+ operator==(const Base & base) const
+ {
+ 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 BitfieldBackend::BitfieldTypes<type> \
+ { \
+ 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.
+#define __SubBitUnion(fieldType, first, last, name) \
+ class : public BitfieldBackend::BitfieldTypes<__DataType> \
+ { \
+ public: \
+ union { \
+ fieldType<first, last> __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.
+//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 EndSubBitUnion(name) \
+ }; \
+ inline operator const __DataType () \
+ { return __data; } \
+ \
+ inline const __DataType operator = (const __DataType & _data) \
+ { __data = _data; } \
+ } name;
+
+//Regular bitfields
+//These define macros for read/write regular bitfield based subbitfields.
+#define SubBitUnion(name, first, last) \
+ __SubBitUnion(Bitfield, first, last, name)
+
+//Regular bitfields
+//These define macros for read/write regular bitfield based subbitfields.
+#define SignedSubBitUnion(name, first, last) \
+ __SubBitUnion(SignedBitfield, 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)
+
#endif // __BASE_BITFIELD_HH__
projects / gem5.git / blobdiff