bitfield.hh revision 4260
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
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
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.
143namespace BitfieldBackend
144{
145    //A base class for all bitfields. It instantiates the actual storage,
146    //and provides getBits and setBits functions for manipulating it. The
147    //Data template parameter is type of the underlying storage.
148    template<class Data>
149    class BitfieldBase
150    {
151      protected:
152        Data __data;
153
154        //This function returns a range of bits from the underlying storage.
155        //It relies on the "bits" function above. It's the user's
156        //responsibility to make sure that there is a properly overloaded
157        //version of this function for whatever type they want to overlay.
158        inline uint64_t
159        getBits(int first, int last)
160        {
161            return bits(__data, first, last);
162        }
163
164        //Similar to the above, but for settings bits with replaceBits.
165        inline void
166        setBits(int first, int last, uint64_t val)
167        {
168            replaceBits(__data, first, last, val);
169        }
170    };
171
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.
175    template<class Type, class Base>
176    class _BitfieldRO : public Base
177    {
178      public:
179        operator const Type ()
180        {
181            return *((Base *)this);
182        }
183    };
184
185    //Similar to the above, but only allows writing.
186    template<class Type, class Base>
187    class _BitfieldWO : public Base
188    {
189      public:
190        const Type operator=(const Type & _data)
191        {
192            *((Base *)this) = _data;
193            return _data;
194        }
195    };
196
197    //This class implements ordinary bitfields, that is a span of bits
198    //who's msb is "first", and who's lsb is "last".
199    template<class Data, int first, int last=first>
200    class _Bitfield : public BitfieldBase<Data>
201    {
202      public:
203        operator const Data ()
204        {
205            return this->getBits(first, last);
206        }
207
208        const Data
209        operator=(const Data & _data)
210        {
211            this->setBits(first, last, _data);
212            return _data;
213        }
214    };
215
216    //When a BitUnion is set up, an underlying class is created which holds
217    //the actual union. This class then inherits from it, and provids the
218    //implementations for various operators. Setting things up this way
219    //prevents having to redefine these functions in every different BitUnion
220    //type. More operators could be implemented in the future, as the need
221    //arises.
222    template <class Type, class Base>
223    class BitUnionOperators : public Base
224    {
225      public:
226        operator const Type ()
227        {
228            return Base::__data;
229        }
230
231        const Type
232        operator=(const Type & _data)
233        {
234            Base::__data = _data;
235        }
236
237        bool
238        operator<(const Base & base)
239        {
240            return Base::__data < base.__data;
241        }
242
243        bool
244        operator==(const Base & base)
245        {
246            return Base::__data == base.__data;
247        }
248    };
249}
250
251//This macro is a backend for other macros that specialize it slightly.
252//First, it creates/extends a namespace "BitfieldUnderlyingClasses" and
253//sticks the class which has the actual union in it, which
254//BitfieldOperators above inherits from. Putting these classes in a special
255//namespace ensures that there will be no collisions with other names as long
256//as the BitUnion names themselves are all distinct and nothing else uses
257//the BitfieldUnderlyingClasses namespace, which is unlikely. The class itself
258//creates a typedef of the "type" parameter called __DataType. This allows
259//the type to propagate outside of the macro itself in a controlled way.
260//Finally, the base storage is defined which BitfieldOperators will refer to
261//in the operators it defines. This macro is intended to be followed by
262//bitfield definitions which will end up inside it's union. As explained
263//above, these is overlayed the __data member in its entirety by each of the
264//bitfields which are defined in the union, creating shared storage with no
265//overhead.
266#define __BitUnion(type, name) \
267    namespace BitfieldUnderlyingClasses \
268    { \
269        class name; \
270    } \
271    class BitfieldUnderlyingClasses::name { \
272      public: \
273        typedef type __DataType; \
274        union { \
275            type __data;\
276
277//This closes off the class and union started by the above macro. It is
278//followed by a typedef which makes "name" refer to a BitfieldOperator
279//class inheriting from the class and union just defined, which completes
280//building up the type for the user.
281#define EndBitUnion(name) \
282        }; \
283    }; \
284    typedef BitfieldBackend::BitUnionOperators< \
285        BitfieldUnderlyingClasses::name::__DataType, \
286        BitfieldUnderlyingClasses::name> name;
287
288//This sets up a bitfield which has other bitfields nested inside of it. The
289//__data member functions like the "underlying storage" of the top level
290//BitUnion. Like everything else, it overlays with the top level storage, so
291//making it a regular bitfield type makes the entire thing function as a
292//regular bitfield when referred to by itself. The operators are defined in
293//the macro itself instead of a class for technical reasons. If someone
294//determines a way to move them to one, please do so.
295#define __SubBitUnion(type, name) \
296        union { \
297            type __data; \
298            inline operator const __DataType () \
299            { return __data; } \
300            \
301            inline const __DataType operator = (const __DataType & _data) \
302            { __data = _data; }
303
304//This closes off the union created above and gives it a name. Unlike the top
305//level BitUnion, we're interested in creating an object instead of a type.
306#define EndSubBitUnion(name) } name;
307
308//The preprocessor will treat everything inside of parenthesis as a single
309//argument even if it has commas in it. This is used to pass in templated
310//classes which typically have commas to seperate their parameters.
311#define wrap(guts) guts
312
313//Read only bitfields
314//This wraps another bitfield class inside a _BitfieldRO class using
315//inheritance. As explained above, the _BitfieldRO class only passes through
316//the conversion operator, so the underlying bitfield can then only be read
317//from.
318#define __BitfieldRO(base) \
319    BitfieldBackend::_BitfieldRO<__DataType, base>
320#define __SubBitUnionRO(name, base) \
321    __SubBitUnion(wrap(_BitfieldRO<__DataType, base>), name)
322
323//Write only bitfields
324//Similar to above, but for making write only versions of bitfields with
325//_BitfieldWO.
326#define __BitfieldWO(base) \
327    BitfieldBackend::_BitfieldWO<__DataType, base>
328#define __SubBitUnionWO(name, base) \
329    __SubBitUnion(wrap(_BitfieldWO<__DataType, base>), name)
330
331//Regular bitfields
332//This uses all of the above to define macros for read/write, read only, and
333//write only versions of regular bitfields.
334#define Bitfield(first, last) \
335    BitfieldBackend::_Bitfield<__DataType, first, last>
336#define SubBitUnion(name, first, last) \
337    __SubBitUnion(Bitfield(first, last), name)
338#define BitfieldRO(first, last) __BitfieldRO(Bitfield(first, last))
339#define SubBitUnionRO(name, first, last) \
340    __SubBitUnionRO(Bitfield(first, last), name)
341#define BitfieldWO(first, last) __BitfieldWO(Bitfield(first, last))
342#define SubBitUnionWO(name, first, last) \
343    __SubBitUnionWO(Bitfield(first, last), name)
344
345//Use this to define an arbitrary type overlayed with bitfields.
346#define BitUnion(type, name) __BitUnion(type, name)
347
348//Use this to define conveniently sized values overlayed with bitfields.
349#define BitUnion64(name) __BitUnion(uint64_t, name)
350#define BitUnion32(name) __BitUnion(uint32_t, name)
351#define BitUnion16(name) __BitUnion(uint16_t, name)
352#define BitUnion8(name) __BitUnion(uint8_t, name)
353
354#endif // __BASE_BITFIELD_HH__
355