bitfield.hh revision 11932:98961d1b51ca 
1/*
2 * Copyright (c) 2017 ARM Limited
3 * All rights reserved
4 *
5 * The license below extends only to copyright in the software and shall
6 * not be construed as granting a license to any other intellectual
7 * property including but not limited to intellectual property relating
8 * to a hardware implementation of the functionality of the software
9 * licensed hereunder.  You may use the software subject to the license
10 * terms below provided that you ensure that this notice is replicated
11 * unmodified and in its entirety in all distributions of the software,
12 * modified or unmodified, in source code or in binary form.
13 *
14 * Copyright (c) 2003-2005 The Regents of The University of Michigan
15 * All rights reserved.
16 *
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions are
19 * met: redistributions of source code must retain the above copyright
20 * notice, this list of conditions and the following disclaimer;
21 * redistributions in binary form must reproduce the above copyright
22 * notice, this list of conditions and the following disclaimer in the
23 * documentation and/or other materials provided with the distribution;
24 * neither the name of the copyright holders nor the names of its
25 * contributors may be used to endorse or promote products derived from
26 * this software without specific prior written permission.
27 *
28 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
29 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
30 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
31 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
32 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
33 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
34 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
35 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
36 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
37 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
38 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
39 *
40 * Authors: Steve Reinhardt
41 *          Nathan Binkert
42 */
43
44#ifndef __BASE_BITFIELD_HH__
45#define __BASE_BITFIELD_HH__
46
47#include <inttypes.h>
48
49/**
50 * Generate a 64-bit mask of 'nbits' 1s, right justified.
51 */
52inline uint64_t
53mask(int nbits)
54{
55    return (nbits == 64) ? (uint64_t)-1LL : (1ULL << nbits) - 1;
56}
57
58
59
60/**
61 * Extract the bitfield from position 'first' to 'last' (inclusive)
62 * from 'val' and right justify it.  MSB is numbered 63, LSB is 0.
63 */
64template <class T>
65inline
66T
67bits(T val, int first, int last)
68{
69    int nbits = first - last + 1;
70    return (val >> last) & mask(nbits);
71}
72
73/**
74 * Extract the bit from this position from 'val' and right justify it.
75 */
76template <class T>
77inline
78T
79bits(T val, int bit)
80{
81    return bits(val, bit, bit);
82}
83
84/**
85 * Mask off the given bits in place like bits() but without shifting.
86 * msb = 63, lsb = 0
87 */
88template <class T>
89inline
90T
91mbits(T val, int first, int last)
92{
93    return val & (mask(first+1) & ~mask(last));
94}
95
96inline uint64_t
97mask(int first, int last)
98{
99    return mbits((uint64_t)-1LL, first, last);
100}
101
102/**
103 * Sign-extend an N-bit value to 64 bits.
104 */
105template <int N>
106inline
107uint64_t
108sext(uint64_t val)
109{
110    int sign_bit = bits(val, N-1, N-1);
111    return sign_bit ? (val | ~mask(N)) : val;
112}
113
114/**
115 * Return val with bits first to last set to bit_val
116 */
117template <class T, class B>
118inline
119T
120insertBits(T val, int first, int last, B bit_val)
121{
122    T t_bit_val = bit_val;
123    T bmask = mask(first - last + 1) << last;
124    return ((t_bit_val << last) & bmask) | (val & ~bmask);
125}
126
127/**
128 * Overloaded for access to only one bit in value
129 */
130template <class T, class B>
131inline
132T
133insertBits(T val, int bit, B bit_val)
134{
135    return insertBits(val, bit, bit, bit_val);
136}
137
138/**
139 * A convenience function to replace bits first to last of val with bit_val
140 * in place.
141 */
142template <class T, class B>
143inline
144void
145replaceBits(T& val, int first, int last, B bit_val)
146{
147    val = insertBits(val, first, last, bit_val);
148}
149
150/** Overloaded function to allow to access only 1 bit*/
151template <class T, class B>
152inline
153void
154replaceBits(T& val, int bit, B bit_val)
155{
156    val = insertBits(val, bit, bit, bit_val);
157}
158/**
159 * Returns the bit position of the MSB that is set in the input
160 */
161inline
162int
163findMsbSet(uint64_t val) {
164    int msb = 0;
165    if (!val)
166        return 0;
167    if (bits(val, 63,32)) { msb += 32; val >>= 32; }
168    if (bits(val, 31,16)) { msb += 16; val >>= 16; }
169    if (bits(val, 15,8))  { msb += 8;  val >>= 8;  }
170    if (bits(val, 7,4))   { msb += 4;  val >>= 4;  }
171    if (bits(val, 3,2))   { msb += 2;  val >>= 2;  }
172    if (bits(val, 1,1))   { msb += 1; }
173    return msb;
174}
175
176/**
177 * Returns the bit position of the LSB that is set in the input
178 */
179inline int
180findLsbSet(uint64_t val) {
181    int lsb = 0;
182    if (!val)
183        return sizeof(val) * 8;
184    if (!bits(val, 31,0)) { lsb += 32; val >>= 32; }
185    if (!bits(val, 15,0)) { lsb += 16; val >>= 16; }
186    if (!bits(val, 7,0))  { lsb += 8;  val >>= 8;  }
187    if (!bits(val, 3,0))  { lsb += 4;  val >>= 4;  }
188    if (!bits(val, 1,0))  { lsb += 2;  val >>= 2;  }
189    if (!bits(val, 0,0))  { lsb += 1; }
190    return lsb;
191}
192
193/**
194 * Checks if a number is a power of two, or zero.
195 */
196template <class T>
197inline bool
198isPow2(T v) {
199   return (v & (v - 1)) == (T)0;
200}
201
202/**
203 * Returns the number of set ones in the provided value.
204 * PD algorithm from
205 * http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
206 */
207inline int
208popCount(uint64_t val) {
209#ifndef __has_builtin
210    #define __has_builtin(foo) 0
211#endif
212#if defined(__GNUC__) || (defined(__clang__) && __has_builtin(__builtin_popcountl))
213    return __builtin_popcountl(val);
214#else
215    const uint64_t m1 = 0x5555555555555555;  // ..010101b
216    const uint64_t m2 = 0x3333333333333333;  // ..110011b
217    const uint64_t m4 = 0x0f0f0f0f0f0f0f0f;  // ..001111b
218    const uint64_t sum = 0x0101010101010101;
219
220    val -= (val >> 1) & m1;               // 2 bits count -> 2 bits
221    val = (val & m2) + ((val >> 2) & m2); // 4 bits count -> 4 bits
222    val = (val + (val >> 4)) & m4;        // 8 bits count -> 8 bits
223    return (val * sum) >> 56;             // horizontal sum
224#endif // defined(__GNUC__) || (defined(__clang__) && __has_builtin(__builtin_popcountl))
225}
226
227/**
228 * Align to the next highest power of two.
229 *
230 * The number passed in is aligned to the next highest power of two,
231 * if it is not already a power of two. Please note that if 0 is
232 * passed in, 0 is returned.
233 *
234 * This code has been modified from the following:
235 * http://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
236 */
237inline uint64_t alignToPowerOfTwo(uint64_t val)
238{
239    val--;
240    val |= val >> 1;
241    val |= val >> 2;
242    val |= val >> 4;
243    val |= val >> 8;
244    val |= val >> 16;
245    val |= val >> 32;
246    val++;
247
248    return val;
249};
250
251#endif // __BASE_BITFIELD_HH__
252