bitfield.hh revision 10400:0655a3d869ad 
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 "base/types.hh"
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 * Extract the bit from this position from 'val' and right justify it.
63 */
64template <class T>
65inline
66T
67bits(T val, int bit)
68{
69    return bits(val, bit, bit);
70}
71
72/**
73 * Mask off the given bits in place like bits() but without shifting.
74 * msb = 63, lsb = 0
75 */
76template <class T>
77inline
78T
79mbits(T val, int first, int last)
80{
81    return val & (mask(first+1) & ~mask(last));
82}
83
84inline uint64_t
85mask(int first, int last)
86{
87    return mbits((uint64_t)-1LL, first, last);
88}
89
90/**
91 * Sign-extend an N-bit value to 64 bits.
92 */
93template <int N>
94inline
95int64_t
96sext(uint64_t val)
97{
98    int sign_bit = bits(val, N-1, N-1);
99    return sign_bit ? (val | ~mask(N)) : val;
100}
101
102/**
103 * Return val with bits first to last set to bit_val
104 */
105template <class T, class B>
106inline
107T
108insertBits(T val, int first, int last, B bit_val)
109{
110    T t_bit_val = bit_val;
111    T bmask = mask(first - last + 1) << last;
112    return ((t_bit_val << last) & bmask) | (val & ~bmask);
113}
114
115/**
116 * Overloaded for access to only one bit in value
117 */
118template <class T, class B>
119inline
120T
121insertBits(T val, int bit, B bit_val)
122{
123    return insertBits(val, bit, bit, bit_val);
124}
125
126/**
127 * A convenience function to replace bits first to last of val with bit_val
128 * in place.
129 */
130template <class T, class B>
131inline
132void
133replaceBits(T& val, int first, int last, B bit_val)
134{
135    val = insertBits(val, first, last, bit_val);
136}
137
138/** Overloaded function to allow to access only 1 bit*/
139template <class T, class B>
140inline
141void
142replaceBits(T& val, int bit, B bit_val)
143{
144    val = insertBits(val, bit, bit, bit_val);
145}
146/**
147 * Returns the bit position of the MSB that is set in the input
148 */
149inline
150int
151findMsbSet(uint64_t val) {
152    int msb = 0;
153    if (!val)
154        return 0;
155    if (bits(val, 63,32)) { msb += 32; val >>= 32; }
156    if (bits(val, 31,16)) { msb += 16; val >>= 16; }
157    if (bits(val, 15,8))  { msb += 8;  val >>= 8;  }
158    if (bits(val, 7,4))   { msb += 4;  val >>= 4;  }
159    if (bits(val, 3,2))   { msb += 2;  val >>= 2;  }
160    if (bits(val, 1,1))   { msb += 1; }
161    return msb;
162}
163
164/**
165 * Returns the bit position of the LSB that is set in the input
166 */
167inline int
168findLsbSet(uint64_t val) {
169    int lsb = 0;
170    if (!val)
171        return sizeof(val) * 8;
172    if (!bits(val, 31,0)) { lsb += 32; val >>= 32; }
173    if (!bits(val, 15,0)) { lsb += 16; val >>= 16; }
174    if (!bits(val, 7,0))  { lsb += 8;  val >>= 8;  }
175    if (!bits(val, 3,0))  { lsb += 4;  val >>= 4;  }
176    if (!bits(val, 1,0))  { lsb += 2;  val >>= 2;  }
177    if (!bits(val, 0,0))  { lsb += 1; }
178    return lsb;
179}
180
181/**
182 * Checks if a number is a power of two, or zero.
183 */
184template <class T>
185inline bool
186isPow2(T v) {
187   return (v & (v - 1)) == (T)0;
188}
189
190/**
191 * Returns the number of set ones in the provided value.
192 * PD algorithm from
193 * http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
194 */
195inline int
196popCount(uint64_t val) {
197#ifndef __has_builtin
198    #define __has_builtin(foo) 0
199#endif
200#if defined(__GNUC__) || (defined(__clang__) && __has_builtin(__builtin_popcountl))
201    return __builtin_popcountl(val);
202#else
203    const uint64_t m1 = 0x5555555555555555;  // ..010101b
204    const uint64_t m2 = 0x3333333333333333;  // ..110011b
205    const uint64_t m4 = 0x0f0f0f0f0f0f0f0f;  // ..001111b
206    const uint64_t sum = 0x0101010101010101;
207
208    val -= (val >> 1) & m1;               // 2 bits count -> 2 bits
209    val = (val & m2) + ((val >> 2) & m2); // 4 bits count -> 4 bits
210    val = (val + (val >> 4)) & m4;        // 8 bits count -> 8 bits
211    return (val * sum) >> 56;             // horizontal sum
212#endif // defined(__GNUC__) || (defined(__clang__) && __has_builtin(__builtin_popcountl))
213}
214#endif // __BASE_BITFIELD_HH__
215