1 /* Integer base 2 logarithm calculation
2 *
3 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
4 * Written by David Howells (dhowells@redhat.com)
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 */
11
12 #ifndef _TOOLS_LINUX_LOG2_H
13 #define _TOOLS_LINUX_LOG2_H
14
15 /*
16 * deal with unrepresentable constant logarithms
17 */
18 extern __attribute__((const, noreturn))
19 int ____ilog2_NaN(void);
20
21 /*
22 * non-constant log of base 2 calculators
23 * - the arch may override these in asm/bitops.h if they can be implemented
24 * more efficiently than using fls() and fls64()
25 * - the arch is not required to handle n==0 if implementing the fallback
26 */
27 static inline __attribute__((const))
__ilog2_u32(u32 n)28 int __ilog2_u32(u32 n)
29 {
30 return fls(n) - 1;
31 }
32
33 static inline __attribute__((const))
__ilog2_u64(u64 n)34 int __ilog2_u64(u64 n)
35 {
36 return fls64(n) - 1;
37 }
38
39 /*
40 * Determine whether some value is a power of two, where zero is
41 * *not* considered a power of two.
42 */
43
44 static inline __attribute__((const))
is_power_of_2(unsigned long n)45 bool is_power_of_2(unsigned long n)
46 {
47 return (n != 0 && ((n & (n - 1)) == 0));
48 }
49
50 /*
51 * round up to nearest power of two
52 */
53 static inline __attribute__((const))
__roundup_pow_of_two(unsigned long n)54 unsigned long __roundup_pow_of_two(unsigned long n)
55 {
56 return 1UL << fls_long(n - 1);
57 }
58
59 /*
60 * round down to nearest power of two
61 */
62 static inline __attribute__((const))
__rounddown_pow_of_two(unsigned long n)63 unsigned long __rounddown_pow_of_two(unsigned long n)
64 {
65 return 1UL << (fls_long(n) - 1);
66 }
67
68 /**
69 * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
70 * @n - parameter
71 *
72 * constant-capable log of base 2 calculation
73 * - this can be used to initialise global variables from constant data, hence
74 * the massive ternary operator construction
75 *
76 * selects the appropriately-sized optimised version depending on sizeof(n)
77 */
78 #define ilog2(n) \
79 ( \
80 __builtin_constant_p(n) ? ( \
81 (n) < 1 ? ____ilog2_NaN() : \
82 (n) & (1ULL << 63) ? 63 : \
83 (n) & (1ULL << 62) ? 62 : \
84 (n) & (1ULL << 61) ? 61 : \
85 (n) & (1ULL << 60) ? 60 : \
86 (n) & (1ULL << 59) ? 59 : \
87 (n) & (1ULL << 58) ? 58 : \
88 (n) & (1ULL << 57) ? 57 : \
89 (n) & (1ULL << 56) ? 56 : \
90 (n) & (1ULL << 55) ? 55 : \
91 (n) & (1ULL << 54) ? 54 : \
92 (n) & (1ULL << 53) ? 53 : \
93 (n) & (1ULL << 52) ? 52 : \
94 (n) & (1ULL << 51) ? 51 : \
95 (n) & (1ULL << 50) ? 50 : \
96 (n) & (1ULL << 49) ? 49 : \
97 (n) & (1ULL << 48) ? 48 : \
98 (n) & (1ULL << 47) ? 47 : \
99 (n) & (1ULL << 46) ? 46 : \
100 (n) & (1ULL << 45) ? 45 : \
101 (n) & (1ULL << 44) ? 44 : \
102 (n) & (1ULL << 43) ? 43 : \
103 (n) & (1ULL << 42) ? 42 : \
104 (n) & (1ULL << 41) ? 41 : \
105 (n) & (1ULL << 40) ? 40 : \
106 (n) & (1ULL << 39) ? 39 : \
107 (n) & (1ULL << 38) ? 38 : \
108 (n) & (1ULL << 37) ? 37 : \
109 (n) & (1ULL << 36) ? 36 : \
110 (n) & (1ULL << 35) ? 35 : \
111 (n) & (1ULL << 34) ? 34 : \
112 (n) & (1ULL << 33) ? 33 : \
113 (n) & (1ULL << 32) ? 32 : \
114 (n) & (1ULL << 31) ? 31 : \
115 (n) & (1ULL << 30) ? 30 : \
116 (n) & (1ULL << 29) ? 29 : \
117 (n) & (1ULL << 28) ? 28 : \
118 (n) & (1ULL << 27) ? 27 : \
119 (n) & (1ULL << 26) ? 26 : \
120 (n) & (1ULL << 25) ? 25 : \
121 (n) & (1ULL << 24) ? 24 : \
122 (n) & (1ULL << 23) ? 23 : \
123 (n) & (1ULL << 22) ? 22 : \
124 (n) & (1ULL << 21) ? 21 : \
125 (n) & (1ULL << 20) ? 20 : \
126 (n) & (1ULL << 19) ? 19 : \
127 (n) & (1ULL << 18) ? 18 : \
128 (n) & (1ULL << 17) ? 17 : \
129 (n) & (1ULL << 16) ? 16 : \
130 (n) & (1ULL << 15) ? 15 : \
131 (n) & (1ULL << 14) ? 14 : \
132 (n) & (1ULL << 13) ? 13 : \
133 (n) & (1ULL << 12) ? 12 : \
134 (n) & (1ULL << 11) ? 11 : \
135 (n) & (1ULL << 10) ? 10 : \
136 (n) & (1ULL << 9) ? 9 : \
137 (n) & (1ULL << 8) ? 8 : \
138 (n) & (1ULL << 7) ? 7 : \
139 (n) & (1ULL << 6) ? 6 : \
140 (n) & (1ULL << 5) ? 5 : \
141 (n) & (1ULL << 4) ? 4 : \
142 (n) & (1ULL << 3) ? 3 : \
143 (n) & (1ULL << 2) ? 2 : \
144 (n) & (1ULL << 1) ? 1 : \
145 (n) & (1ULL << 0) ? 0 : \
146 ____ilog2_NaN() \
147 ) : \
148 (sizeof(n) <= 4) ? \
149 __ilog2_u32(n) : \
150 __ilog2_u64(n) \
151 )
152
153 /**
154 * roundup_pow_of_two - round the given value up to nearest power of two
155 * @n - parameter
156 *
157 * round the given value up to the nearest power of two
158 * - the result is undefined when n == 0
159 * - this can be used to initialise global variables from constant data
160 */
161 #define roundup_pow_of_two(n) \
162 ( \
163 __builtin_constant_p(n) ? ( \
164 (n == 1) ? 1 : \
165 (1UL << (ilog2((n) - 1) + 1)) \
166 ) : \
167 __roundup_pow_of_two(n) \
168 )
169
170 /**
171 * rounddown_pow_of_two - round the given value down to nearest power of two
172 * @n - parameter
173 *
174 * round the given value down to the nearest power of two
175 * - the result is undefined when n == 0
176 * - this can be used to initialise global variables from constant data
177 */
178 #define rounddown_pow_of_two(n) \
179 ( \
180 __builtin_constant_p(n) ? ( \
181 (1UL << ilog2(n))) : \
182 __rounddown_pow_of_two(n) \
183 )
184
185 #endif /* _TOOLS_LINUX_LOG2_H */
186