1//
2// bitfield.c - extract and set bit fields
3//
4// Written by Eryk Vershen
5//
6// See comments in bitfield.h
7//
8
9/*
10 * Copyright 1996, 1997 by Apple Computer, Inc.
11 *              All Rights Reserved
12 *
13 * Permission to use, copy, modify, and distribute this software and
14 * its documentation for any purpose and without fee is hereby granted,
15 * provided that the above copyright notice appears in all copies and
16 * that both the copyright notice and this permission notice appear in
17 * supporting documentation.
18 *
19 * APPLE COMPUTER DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
20 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
21 * FOR A PARTICULAR PURPOSE.
22 *
23 * IN NO EVENT SHALL APPLE COMPUTER BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
24 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
25 * LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
26 * NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
27 * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
28 */
29
30#include <stdint.h>
31#include "bitfield.h"
32
33
34//
35// Defines
36//
37
38
39//
40// Types
41//
42
43
44//
45// Global Constants
46//
47const uint32_t masks[] = {
48    0x00000000,
49    0x00000001, 0x00000003, 0x00000007, 0x0000000F,
50    0x0000001F, 0x0000003F, 0x0000007F, 0x000000FF,
51    0x000001FF, 0x000003FF, 0x000007FF, 0x00000FFF,
52    0x00001FFF, 0x00003FFF, 0x00007FFF, 0x0000FFFF,
53    0x0001FFFF, 0x0003FFFF, 0x0007FFFF, 0x000FFFFF,
54    0x001FFFFF, 0x003FFFFF, 0x007FFFFF, 0x00FFFFFF,
55    0x01FFFFFF, 0x03FFFFFF, 0x07FFFFFF, 0x0FFFFFFF,
56    0x1FFFFFFF, 0x3FFFFFFF, 0x7FFFFFFF, 0xFFFFFFFF
57};
58
59
60//
61// Global Variables
62//
63
64
65//
66// Forward declarations
67//
68
69
70//
71// Routines
72//
73uint32_t
74bitfield_set(uint32_t *bf, int base, int length, uint32_t value)
75{
76    uint32_t t;
77    uint32_t m;
78    int s;
79
80    // compute shift & mask, coerce value to correct number of bits,
81    // zap the old bits and stuff the new value
82    // return the masked value in case someone wants it.
83    s = (base + 1) - length;
84    m = masks[length];
85    t = value & m;
86    *bf = (*bf & ~(m << s)) | (t << s);
87    return t;
88}
89
90
91uint32_t
92bitfield_get(uint32_t bf, int base, int length)
93{
94    uint32_t m;
95    int s;
96
97    // compute shift & mask
98    // return the correct number of bits (shifted to low end)
99    s = (base + 1) - length;
100    m = masks[length];
101    return ((bf >> s) & m);
102}
103