1/*
2 * Copyright (c) 2003-2005 The Regents of The University of Michigan
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;

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126 if (bits(val, 15,8)) { msb += 8; val >>= 8; }
127 if (bits(val, 7,4)) { msb += 4; val >>= 4; }
128 if (bits(val, 3,2)) { msb += 2; val >>= 2; }
129 if (bits(val, 1,1)) { msb += 1; }
130 return msb;
131}
132
133// The following implements the BitUnion system of defining bitfields
134//on top of an underlying class. This is done through the pervasive use of
135//both named and unnamed unions which all contain the same actual storage.
136//Since they're unioned with each other, all of these storage locations
137//overlap. This allows all of the bitfields to manipulate the same data
138//without having to have access to each other. More details are provided with the
139//individual components.
140
141//This namespace is for classes which implement the backend of the BitUnion
142//stuff. Don't use any of these directly, except for the Bitfield classes in
143//the *BitfieldTypes class(es).
144namespace BitfieldBackend
145{
146 //A base class for all bitfields. It instantiates the actual storage,
147 //and provides getBits and setBits functions for manipulating it. The
148 //Data template parameter is type of the underlying storage.
149 template<class Data>
150 class BitfieldBase
151 {

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165 //Similar to the above, but for settings bits with replaceBits.
166 inline void
167 setBits(int first, int last, uint64_t val)
168 {
169 replaceBits(__data, first, last, val);
170 }
171 };
172
173 //This class contains all the "regular" bitfield classes. It is inherited
174 //by all BitUnions which give them access to those types.
175 template<class Type>
176 class RegularBitfieldTypes
177 {
178 protected:
179 //This class implements ordinary bitfields, that is a span of bits
180 //who's msb is "first", and who's lsb is "last".
181 template<int first, int last=first>
182 class Bitfield : public BitfieldBase<Type>
183 {
184 public:
185 operator const Type ()
186 {
187 return this->getBits(first, last);
188 }
189
190 const Type
191 operator=(const Type & _data)
192 {
193 this->setBits(first, last, _data);
194 return _data;
195 }
196 };
197
198 //A class which specializes the above so that it can only be read
199 //from. This is accomplished explicitly making sure the assignment
200 //operator is blocked. The conversion operator is carried through
201 //inheritance. This will unfortunately need to be copied into each
202 //bitfield type due to limitations with how templates work
203 template<int first, int last=first>
204 class BitfieldRO : public Bitfield<first, last>
205 {
206 private:
207 const Type
208 operator=(const Type & _data);
209 };
210
211 //Similar to the above, but only allows writing.
212 template<int first, int last=first>
213 class BitfieldWO : public Bitfield<first, last>
214 {
215 private:
216 operator const Type ();
217
218 public:
219 const Type operator=(const Type & _data)
220 {
221 *((Bitfield<first, last> *)this) = _data;
222 return _data;
223 }
224 };
225 };
226
227 template<class Type>
228 class BitfieldTypes : public RegularBitfieldTypes<Type>
229 {};
230
231 //When a BitUnion is set up, an underlying class is created which holds
232 //the actual union. This class then inherits from it, and provids the
233 //implementations for various operators. Setting things up this way
234 //prevents having to redefine these functions in every different BitUnion
235 //type. More operators could be implemented in the future, as the need
236 //arises.
237 template <class Type, class Base>
238 class BitUnionOperators : public Base

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278//above, these is overlayed the __data member in its entirety by each of the
279//bitfields which are defined in the union, creating shared storage with no
280//overhead.
281#define __BitUnion(type, name) \
282 namespace BitfieldUnderlyingClasses \
283 { \
284 class name; \
285 } \
286 class BitfieldUnderlyingClasses::name : \
287 public BitfieldBackend::BitfieldTypes<type> \
288 { \
289 public: \
290 typedef type __DataType; \
291 union { \
292 type __data;\
293
294//This closes off the class and union started by the above macro. It is
295//followed by a typedef which makes "name" refer to a BitfieldOperator
296//class inheriting from the class and union just defined, which completes

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301 typedef BitfieldBackend::BitUnionOperators< \
302 BitfieldUnderlyingClasses::name::__DataType, \
303 BitfieldUnderlyingClasses::name> name;
304
305//This sets up a bitfield which has other bitfields nested inside of it. The
306//__data member functions like the "underlying storage" of the top level
307//BitUnion. Like everything else, it overlays with the top level storage, so
308//making it a regular bitfield type makes the entire thing function as a
309//regular bitfield when referred to by itself.
310#define __SubBitUnion(fieldType, first, last, name) \
311 class : public BitfieldBackend::BitfieldTypes<__DataType> \
312 { \
313 public: \
314 union { \
315 fieldType<first, last> __data;
316
317//This closes off the union created above and gives it a name. Unlike the top
318//level BitUnion, we're interested in creating an object instead of a type.
319//The operators are defined in the macro itself instead of a class for
320//technical reasons. If someone determines a way to move them to one, please
321//do so.
322#define EndSubBitUnion(name) \
323 }; \
324 inline operator const __DataType () \
325 { return __data; } \
326 \
327 inline const __DataType operator = (const __DataType & _data) \
328 { __data = _data; } \
329 } name;
330
331//Regular bitfields
332//These define macros for read/write regular bitfield based subbitfields.
333#define SubBitUnion(name, first, last) \
334 __SubBitUnion(Bitfield, first, last, name)
335
336//Use this to define an arbitrary type overlayed with bitfields.
337#define BitUnion(type, name) __BitUnion(type, name)
338
339//Use this to define conveniently sized values overlayed with bitfields.
340#define BitUnion64(name) __BitUnion(uint64_t, name)
341#define BitUnion32(name) __BitUnion(uint32_t, name)
342#define BitUnion16(name) __BitUnion(uint16_t, name)
343#define BitUnion8(name) __BitUnion(uint8_t, name)
344
345#endif // __BASE_BITFIELD_HH__