bitfield.hh revision 4070:74449a198a44 
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#endif // __BASE_BITFIELD_HH__
116