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;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Steve Reinhardt
29 * Nathan Binkert
30 */
31
32#ifndef __BASE_BITFIELD_HH__
33#define __BASE_BITFIELD_HH__
34
35#include <inttypes.h>
36
37/**
38 * Generate a 64-bit mask of 'nbits' 1s, right justified.
39 */
40inline uint64_t
41mask(int nbits)
42{
43 return (nbits == 64) ? (uint64_t)-1LL : (1ULL << nbits) - 1;
44}
45
46
47
48/**
49 * Extract the bitfield from position 'first' to 'last' (inclusive)
50 * from 'val' and right justify it. MSB is numbered 63, LSB is 0.
51 */
52template <class T>
53inline
54T
55bits(T val, int first, int last)
56{
57 int nbits = first - last + 1;
58 return (val >> last) & mask(nbits);
59}
60
61/**
62 * Mask off the given bits in place like bits() but without shifting.
63 * msb = 63, lsb = 0
64 */
65template <class T>
66inline
67T
68mbits(T val, int first, int last)
69{
70 return val & (mask(first+1) & ~mask(last));
71}
72
73inline uint64_t
74mask(int first, int last)
75{
76 return mbits((uint64_t)-1LL, first, last);
77}
78
79/**
80 * Sign-extend an N-bit value to 64 bits.
81 */
82template <int N>
83inline
84int64_t
85sext(uint64_t val)
86{
87 int sign_bit = bits(val, N-1, N-1);
88 return sign_bit ? (val | ~mask(N)) : val;
89}
90
91/**
92 * Return val with bits first to last set to bit_val
93 */
94template <class T, class B>
95inline
96T
97insertBits(T val, int first, int last, B bit_val)
98{
99 T bmask = mask(first - last + 1) << last;
100 return ((bit_val << last) & bmask) | (val & ~bmask);
101}
102
103/**
104 * A convenience function to replace bits first to last of val with bit_val
105 * in place.
106 */
107template <class T, class B>
108inline
109void
110replaceBits(T& val, int first, int last, B bit_val)
111{
112 val = insertBits(val, first, last, bit_val);
113}
114
115/**
116 * Returns the bit position of the MSB that is set in the input
117 */
118inline
119int
120findMsbSet(uint64_t val) {
121 int msb = 0;
122 if (!val)
123 return 0;
124 if (bits(val, 63,32)) { msb += 32; val >>= 32; }
125 if (bits(val, 31,16)) { msb += 16; val >>= 16; }
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 extensive use of
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 know about each other. More details are provided with the
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 this directly! Use the macros at the end instead.
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 {
152 protected:
153 Data __data;
154
155 //This function returns a range of bits from the underlying storage.
156 //It relies on the "bits" function above. It's the user's
157 //responsibility to make sure that there is a properly overloaded
158 //version of this function for whatever type they want to overlay.
159 inline uint64_t
160 getBits(int first, int last)
161 {
162 return bits(__data, first, last);
163 }
164
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
172 //A class which specializes a given base so that it can only be read
173 //from. This is accomplished by only passing through the conversion
174 //operator and explicitly making sure the assignment operator is blocked.
175 template<class Type, class Base>
176 class _BitfieldRO : public Base
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 private:
179 const Type
180 operator=(const Type & _data);
181
182 public:
183 operator const Type ()
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 {
185 return *((Base *)this);
186 }
187 };
184 public:
185 operator const Type ()
186 {
187 return this->getBits(first, last);
188 }
189
189 //Similar to the above, but only allows writing.
190 template<class Type, class Base>
191 class _BitfieldWO : public Base
192 {
193 private:
194 operator const Type ();
190 const Type
191 operator=(const Type & _data)
192 {
193 this->setBits(first, last, _data);
194 return _data;
195 }
196 };
197
196 public:
197 const Type operator=(const Type & _data)
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 {
199 *((Base *)this) = _data;
200 return _data;
201 }
202 };
206 private:
207 const Type
208 operator=(const Type & _data);
209 };
210
204 //This class implements ordinary bitfields, that is a span of bits
205 //who's msb is "first", and who's lsb is "last".
206 template<class Data, int first, int last=first>
207 class _Bitfield : public BitfieldBase<Data>
208 {
209 public:
210 operator const Data ()
211 //Similar to the above, but only allows writing.
212 template<int first, int last=first>
213 class BitfieldWO : public Bitfield<first, last>
214 {
212 return this->getBits(first, last);
213 }
215 private:
216 operator const Type ();
217
215 const Data
216 operator=(const Data & _data)
217 {
218 this->setBits(first, last, _data);
219 return _data;
220 }
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
239 {
240 public:
241 operator const Type ()
242 {
243 return Base::__data;
244 }
245
246 const Type
247 operator=(const Type & _data)
248 {
249 Base::__data = _data;
250 }
251
252 bool
253 operator<(const Base & base)
254 {
255 return Base::__data < base.__data;
256 }
257
258 bool
259 operator==(const Base & base)
260 {
261 return Base::__data == base.__data;
262 }
263 };
264}
265
266//This macro is a backend for other macros that specialize it slightly.
267//First, it creates/extends a namespace "BitfieldUnderlyingClasses" and
268//sticks the class which has the actual union in it, which
269//BitfieldOperators above inherits from. Putting these classes in a special
270//namespace ensures that there will be no collisions with other names as long
271//as the BitUnion names themselves are all distinct and nothing else uses
272//the BitfieldUnderlyingClasses namespace, which is unlikely. The class itself
273//creates a typedef of the "type" parameter called __DataType. This allows
274//the type to propagate outside of the macro itself in a controlled way.
275//Finally, the base storage is defined which BitfieldOperators will refer to
276//in the operators it defines. This macro is intended to be followed by
277//bitfield definitions which will end up inside it's union. As explained
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 } \
278 class BitfieldUnderlyingClasses::name { \
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
297//building up the type for the user.
298#define EndBitUnion(name) \
299 }; \
300 }; \
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
299//regular bitfield when referred to by itself. The operators are defined in
300//the macro itself instead of a class for technical reasons. If someone
301//determines a way to move them to one, please do so.
302#define __SubBitUnion(type, name) \
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 { \
304 type __data; \
305 inline operator const __DataType () \
306 { return __data; } \
307 \
308 inline const __DataType operator = (const __DataType & _data) \
309 { __data = _data; }
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.
313#define EndSubBitUnion(name) } name;
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
315//The preprocessor will treat everything inside of parenthesis as a single
316//argument even if it has commas in it. This is used to pass in templated
317//classes which typically have commas to seperate their parameters.
318#define wrap(guts) guts
319
320//Read only bitfields
321//This wraps another bitfield class inside a _BitfieldRO class using
322//inheritance. As explained above, the _BitfieldRO class only passes through
323//the conversion operator, so the underlying bitfield can then only be read
324//from.
325#define __BitfieldRO(base) \
326 BitfieldBackend::_BitfieldRO<__DataType, base>
327#define __SubBitUnionRO(name, base) \
328 __SubBitUnion(wrap(_BitfieldRO<__DataType, base>), name)
329
330//Write only bitfields
331//Similar to above, but for making write only versions of bitfields with
332//_BitfieldWO.
333#define __BitfieldWO(base) \
334 BitfieldBackend::_BitfieldWO<__DataType, base>
335#define __SubBitUnionWO(name, base) \
336 __SubBitUnion(wrap(_BitfieldWO<__DataType, base>), name)
337
331//Regular bitfields
339//This uses all of the above to define macros for read/write, read only, and
340//write only versions of regular bitfields.
341#define Bitfield(first, last) \
342 BitfieldBackend::_Bitfield<__DataType, first, last>
332//These define macros for read/write regular bitfield based subbitfields.
333#define SubBitUnion(name, first, last) \
344 __SubBitUnion(Bitfield(first, last), name)
345#define BitfieldRO(first, last) __BitfieldRO(Bitfield(first, last))
346#define SubBitUnionRO(name, first, last) \
347 __SubBitUnionRO(Bitfield(first, last), name)
348#define BitfieldWO(first, last) __BitfieldWO(Bitfield(first, last))
349#define SubBitUnionWO(name, first, last) \
350 __SubBitUnionWO(Bitfield(first, last), name)
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__