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f0d1b0b3 DH |
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 _LINUX_LOG2_H | |
13 | #define _LINUX_LOG2_H | |
14 | ||
15 | #include <linux/types.h> | |
16 | #include <linux/bitops.h> | |
17 | ||
f0d1b0b3 DH |
18 | /* |
19 | * non-constant log of base 2 calculators | |
20 | * - the arch may override these in asm/bitops.h if they can be implemented | |
21 | * more efficiently than using fls() and fls64() | |
22 | * - the arch is not required to handle n==0 if implementing the fallback | |
23 | */ | |
24 | #ifndef CONFIG_ARCH_HAS_ILOG2_U32 | |
25 | static inline __attribute__((const)) | |
26 | int __ilog2_u32(u32 n) | |
27 | { | |
28 | return fls(n) - 1; | |
29 | } | |
30 | #endif | |
31 | ||
32 | #ifndef CONFIG_ARCH_HAS_ILOG2_U64 | |
33 | static inline __attribute__((const)) | |
34 | int __ilog2_u64(u64 n) | |
35 | { | |
36 | return fls64(n) - 1; | |
37 | } | |
38 | #endif | |
39 | ||
a1c4d24e RD |
40 | /** |
41 | * is_power_of_2() - check if a value is a power of two | |
42 | * @n: the value to check | |
43 | * | |
44 | * Determine whether some value is a power of two, where zero is | |
63c2f782 | 45 | * *not* considered a power of two. |
a1c4d24e | 46 | * Return: true if @n is a power of 2, otherwise false. |
63c2f782 | 47 | */ |
63c2f782 RD |
48 | static inline __attribute__((const)) |
49 | bool is_power_of_2(unsigned long n) | |
50 | { | |
51 | return (n != 0 && ((n & (n - 1)) == 0)); | |
52 | } | |
53 | ||
a1c4d24e RD |
54 | /** |
55 | * __roundup_pow_of_two() - round up to nearest power of two | |
56 | * @n: value to round up | |
312a0c17 DH |
57 | */ |
58 | static inline __attribute__((const)) | |
59 | unsigned long __roundup_pow_of_two(unsigned long n) | |
60 | { | |
61 | return 1UL << fls_long(n - 1); | |
62 | } | |
63 | ||
a1c4d24e RD |
64 | /** |
65 | * __rounddown_pow_of_two() - round down to nearest power of two | |
66 | * @n: value to round down | |
b311e921 RD |
67 | */ |
68 | static inline __attribute__((const)) | |
69 | unsigned long __rounddown_pow_of_two(unsigned long n) | |
70 | { | |
71 | return 1UL << (fls_long(n) - 1); | |
72 | } | |
73 | ||
f0d1b0b3 | 74 | /** |
a1c4d24e RD |
75 | * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value |
76 | * @n: parameter | |
f0d1b0b3 DH |
77 | * |
78 | * constant-capable log of base 2 calculation | |
79 | * - this can be used to initialise global variables from constant data, hence | |
a1c4d24e | 80 | * the massive ternary operator construction |
f0d1b0b3 DH |
81 | * |
82 | * selects the appropriately-sized optimised version depending on sizeof(n) | |
83 | */ | |
84 | #define ilog2(n) \ | |
85 | ( \ | |
86 | __builtin_constant_p(n) ? ( \ | |
474c9015 | 87 | (n) < 2 ? 0 : \ |
f0d1b0b3 DH |
88 | (n) & (1ULL << 63) ? 63 : \ |
89 | (n) & (1ULL << 62) ? 62 : \ | |
90 | (n) & (1ULL << 61) ? 61 : \ | |
91 | (n) & (1ULL << 60) ? 60 : \ | |
92 | (n) & (1ULL << 59) ? 59 : \ | |
93 | (n) & (1ULL << 58) ? 58 : \ | |
94 | (n) & (1ULL << 57) ? 57 : \ | |
95 | (n) & (1ULL << 56) ? 56 : \ | |
96 | (n) & (1ULL << 55) ? 55 : \ | |
97 | (n) & (1ULL << 54) ? 54 : \ | |
98 | (n) & (1ULL << 53) ? 53 : \ | |
99 | (n) & (1ULL << 52) ? 52 : \ | |
100 | (n) & (1ULL << 51) ? 51 : \ | |
101 | (n) & (1ULL << 50) ? 50 : \ | |
102 | (n) & (1ULL << 49) ? 49 : \ | |
103 | (n) & (1ULL << 48) ? 48 : \ | |
104 | (n) & (1ULL << 47) ? 47 : \ | |
105 | (n) & (1ULL << 46) ? 46 : \ | |
106 | (n) & (1ULL << 45) ? 45 : \ | |
107 | (n) & (1ULL << 44) ? 44 : \ | |
108 | (n) & (1ULL << 43) ? 43 : \ | |
109 | (n) & (1ULL << 42) ? 42 : \ | |
110 | (n) & (1ULL << 41) ? 41 : \ | |
111 | (n) & (1ULL << 40) ? 40 : \ | |
112 | (n) & (1ULL << 39) ? 39 : \ | |
113 | (n) & (1ULL << 38) ? 38 : \ | |
114 | (n) & (1ULL << 37) ? 37 : \ | |
115 | (n) & (1ULL << 36) ? 36 : \ | |
116 | (n) & (1ULL << 35) ? 35 : \ | |
117 | (n) & (1ULL << 34) ? 34 : \ | |
118 | (n) & (1ULL << 33) ? 33 : \ | |
119 | (n) & (1ULL << 32) ? 32 : \ | |
120 | (n) & (1ULL << 31) ? 31 : \ | |
121 | (n) & (1ULL << 30) ? 30 : \ | |
122 | (n) & (1ULL << 29) ? 29 : \ | |
123 | (n) & (1ULL << 28) ? 28 : \ | |
124 | (n) & (1ULL << 27) ? 27 : \ | |
125 | (n) & (1ULL << 26) ? 26 : \ | |
126 | (n) & (1ULL << 25) ? 25 : \ | |
127 | (n) & (1ULL << 24) ? 24 : \ | |
128 | (n) & (1ULL << 23) ? 23 : \ | |
129 | (n) & (1ULL << 22) ? 22 : \ | |
130 | (n) & (1ULL << 21) ? 21 : \ | |
131 | (n) & (1ULL << 20) ? 20 : \ | |
132 | (n) & (1ULL << 19) ? 19 : \ | |
133 | (n) & (1ULL << 18) ? 18 : \ | |
134 | (n) & (1ULL << 17) ? 17 : \ | |
135 | (n) & (1ULL << 16) ? 16 : \ | |
136 | (n) & (1ULL << 15) ? 15 : \ | |
137 | (n) & (1ULL << 14) ? 14 : \ | |
138 | (n) & (1ULL << 13) ? 13 : \ | |
139 | (n) & (1ULL << 12) ? 12 : \ | |
140 | (n) & (1ULL << 11) ? 11 : \ | |
141 | (n) & (1ULL << 10) ? 10 : \ | |
142 | (n) & (1ULL << 9) ? 9 : \ | |
143 | (n) & (1ULL << 8) ? 8 : \ | |
144 | (n) & (1ULL << 7) ? 7 : \ | |
145 | (n) & (1ULL << 6) ? 6 : \ | |
146 | (n) & (1ULL << 5) ? 5 : \ | |
147 | (n) & (1ULL << 4) ? 4 : \ | |
148 | (n) & (1ULL << 3) ? 3 : \ | |
149 | (n) & (1ULL << 2) ? 2 : \ | |
474c9015 | 150 | 1 ) : \ |
f0d1b0b3 DH |
151 | (sizeof(n) <= 4) ? \ |
152 | __ilog2_u32(n) : \ | |
153 | __ilog2_u64(n) \ | |
154 | ) | |
155 | ||
312a0c17 DH |
156 | /** |
157 | * roundup_pow_of_two - round the given value up to nearest power of two | |
a1c4d24e | 158 | * @n: parameter |
312a0c17 | 159 | * |
6fb189c2 | 160 | * round the given value up to the nearest power of two |
312a0c17 DH |
161 | * - the result is undefined when n == 0 |
162 | * - this can be used to initialise global variables from constant data | |
163 | */ | |
164 | #define roundup_pow_of_two(n) \ | |
165 | ( \ | |
166 | __builtin_constant_p(n) ? ( \ | |
1a06a52e | 167 | (n == 1) ? 1 : \ |
312a0c17 DH |
168 | (1UL << (ilog2((n) - 1) + 1)) \ |
169 | ) : \ | |
170 | __roundup_pow_of_two(n) \ | |
171 | ) | |
172 | ||
b311e921 RD |
173 | /** |
174 | * rounddown_pow_of_two - round the given value down to nearest power of two | |
a1c4d24e | 175 | * @n: parameter |
b311e921 RD |
176 | * |
177 | * round the given value down to the nearest power of two | |
178 | * - the result is undefined when n == 0 | |
179 | * - this can be used to initialise global variables from constant data | |
180 | */ | |
181 | #define rounddown_pow_of_two(n) \ | |
182 | ( \ | |
183 | __builtin_constant_p(n) ? ( \ | |
b311e921 RD |
184 | (1UL << ilog2(n))) : \ |
185 | __rounddown_pow_of_two(n) \ | |
186 | ) | |
187 | ||
a1c4d24e RD |
188 | static inline __attribute_const__ |
189 | int __order_base_2(unsigned long n) | |
190 | { | |
191 | return n > 1 ? ilog2(n - 1) + 1 : 0; | |
192 | } | |
193 | ||
de9330d1 RD |
194 | /** |
195 | * order_base_2 - calculate the (rounded up) base 2 order of the argument | |
196 | * @n: parameter | |
197 | * | |
198 | * The first few values calculated by this routine: | |
199 | * ob2(0) = 0 | |
200 | * ob2(1) = 0 | |
201 | * ob2(2) = 1 | |
202 | * ob2(3) = 2 | |
203 | * ob2(4) = 2 | |
204 | * ob2(5) = 3 | |
205 | * ... and so on. | |
206 | */ | |
29905b52 AB |
207 | #define order_base_2(n) \ |
208 | ( \ | |
209 | __builtin_constant_p(n) ? ( \ | |
210 | ((n) == 0 || (n) == 1) ? 0 : \ | |
211 | ilog2((n) - 1) + 1) : \ | |
212 | __order_base_2(n) \ | |
213 | ) | |
f0d1b0b3 | 214 | #endif /* _LINUX_LOG2_H */ |