1/*****************************************************************************/
2/* */
3/* shift.c */
4/* */
5/* Safe shift routines */
6/* */
7/* */
8/* */
9/* (C) 2003 Ullrich von Bassewitz */
10/* Roemerstrasse 52 */
11/* D-70794 Filderstadt */
12/* EMail: uz@cc65.org */
13/* */
14/* */
15/* This software is provided 'as-is', without any expressed or implied */
16/* warranty. In no event will the authors be held liable for any damages */
17/* arising from the use of this software. */
18/* */
19/* Permission is granted to anyone to use this software for any purpose, */
20/* including commercial applications, and to alter it and redistribute it */
21/* freely, subject to the following restrictions: */
22/* */
23/* 1. The origin of this software must not be misrepresented; you must not */
24/* claim that you wrote the original software. If you use this software */
25/* in a product, an acknowledgment in the product documentation would be */
26/* appreciated but is not required. */
27/* 2. Altered source versions must be plainly marked as such, and must not */
28/* be misrepresented as being the original software. */
29/* 3. This notice may not be removed or altered from any source */
30/* distribution. */
31/* */
32/*****************************************************************************/
33
34
35
36/* According to the C standard, shifting a data type by the number of bits it
37** has causes undefined behaviour. So
38**
39** unsigned long l = 1;
40** unsigned u =32;
41** l <<= u;
42**
43** may be illegal. The functions in this module behave safely in that respect,
44** and they use proper casting to distinguish signed from unsigned shifts.
45** They are not a general purpose replacement for the shift operator!
46*/
47
48
49
50#include <limits.h>
51
52/* common */
53#include "shift.h"
54
55
56
57/*****************************************************************************/
58/* Code */
59/*****************************************************************************/
60
61
62
63long asl_l (long l, unsigned count)
64/* Arithmetic shift left l by count. */
65{
66 while (1) {
67 if (count >= CHAR_BIT * sizeof (l)) {
68 l <<= (CHAR_BIT * sizeof (l) - 1);
69 count -= (CHAR_BIT * sizeof (l) - 1);
70 } else {
71 l <<= count;
72 break;
73 }
74 }
75 return l;
76}
77
78
79
80long asr_l (long l, unsigned count)
81/* Arithmetic shift right l by count */
82{
83 while (1) {
84 if (count >= CHAR_BIT * sizeof (l)) {
85 l >>= (CHAR_BIT * sizeof (l) - 1);
86 count -= (CHAR_BIT * sizeof (l) - 1);
87 } else {
88 l >>= count;
89 break;
90 }
91 }
92 return l;
93}
94
95
96
97unsigned long shl_l (unsigned long l, unsigned count)
98/* Logical shift left l by count */
99{
100 while (1) {
101 if (count >= CHAR_BIT * sizeof (l)) {
102 l <<= (CHAR_BIT * sizeof (l) - 1);
103 count -= (CHAR_BIT * sizeof (l) - 1);
104 } else {
105 l <<= count;
106 break;
107 }
108 }
109 return l;
110}
111
112
113
114unsigned long shr_l (unsigned long l, unsigned count)
115/* Logical shift right l by count */
116{
117 while (1) {
118 if (count >= CHAR_BIT * sizeof (l)) {
119 l >>= (CHAR_BIT * sizeof (l) - 1);
120 count -= (CHAR_BIT * sizeof (l) - 1);
121 } else {
122 l >>= count;
123 break;
124 }
125 }
126 return l;
127}
128