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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 | * SPDX-License-Identifier: GPL-2.0+ | |
7 | */ | |
8 | ||
9 | #ifndef _LINUX_LOG2_H | |
10 | #define _LINUX_LOG2_H | |
11 | ||
12 | #include <linux/types.h> | |
13 | #include <linux/bitops.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 | #ifndef CONFIG_ARCH_HAS_ILOG2_U32 | |
28 | static inline __attribute__((const)) | |
29 | int __ilog2_u32(u32 n) | |
30 | { | |
31 | return fls(n) - 1; | |
32 | } | |
33 | #endif | |
34 | ||
35 | #ifndef CONFIG_ARCH_HAS_ILOG2_U64 | |
36 | static inline __attribute__((const)) | |
37 | int __ilog2_u64(u64 n) | |
38 | { | |
39 | return fls64(n) - 1; | |
40 | } | |
41 | #endif | |
42 | ||
43 | /* | |
44 | * Determine whether some value is a power of two, where zero is | |
45 | * *not* considered a power of two. | |
46 | */ | |
47 | ||
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 | ||
54 | /* | |
55 | * round up to nearest power of two | |
56 | */ | |
57 | static inline __attribute__((const)) | |
58 | unsigned long __roundup_pow_of_two(unsigned long n) | |
59 | { | |
60 | return 1UL << fls_long(n - 1); | |
61 | } | |
62 | ||
63 | /* | |
64 | * round down to nearest power of two | |
65 | */ | |
66 | static inline __attribute__((const)) | |
67 | unsigned long __rounddown_pow_of_two(unsigned long n) | |
68 | { | |
69 | return 1UL << (fls_long(n) - 1); | |
70 | } | |
71 | ||
72 | /** | |
73 | * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value | |
74 | * @n - parameter | |
75 | * | |
76 | * constant-capable log of base 2 calculation | |
77 | * - this can be used to initialise global variables from constant data, hence | |
78 | * the massive ternary operator construction | |
79 | * | |
80 | * selects the appropriately-sized optimised version depending on sizeof(n) | |
81 | */ | |
82 | #define ilog2(n) \ | |
83 | ( \ | |
84 | __builtin_constant_p(n) ? ( \ | |
85 | (n) < 1 ? ____ilog2_NaN() : \ | |
86 | (n) & (1ULL << 63) ? 63 : \ | |
87 | (n) & (1ULL << 62) ? 62 : \ | |
88 | (n) & (1ULL << 61) ? 61 : \ | |
89 | (n) & (1ULL << 60) ? 60 : \ | |
90 | (n) & (1ULL << 59) ? 59 : \ | |
91 | (n) & (1ULL << 58) ? 58 : \ | |
92 | (n) & (1ULL << 57) ? 57 : \ | |
93 | (n) & (1ULL << 56) ? 56 : \ | |
94 | (n) & (1ULL << 55) ? 55 : \ | |
95 | (n) & (1ULL << 54) ? 54 : \ | |
96 | (n) & (1ULL << 53) ? 53 : \ | |
97 | (n) & (1ULL << 52) ? 52 : \ | |
98 | (n) & (1ULL << 51) ? 51 : \ | |
99 | (n) & (1ULL << 50) ? 50 : \ | |
100 | (n) & (1ULL << 49) ? 49 : \ | |
101 | (n) & (1ULL << 48) ? 48 : \ | |
102 | (n) & (1ULL << 47) ? 47 : \ | |
103 | (n) & (1ULL << 46) ? 46 : \ | |
104 | (n) & (1ULL << 45) ? 45 : \ | |
105 | (n) & (1ULL << 44) ? 44 : \ | |
106 | (n) & (1ULL << 43) ? 43 : \ | |
107 | (n) & (1ULL << 42) ? 42 : \ | |
108 | (n) & (1ULL << 41) ? 41 : \ | |
109 | (n) & (1ULL << 40) ? 40 : \ | |
110 | (n) & (1ULL << 39) ? 39 : \ | |
111 | (n) & (1ULL << 38) ? 38 : \ | |
112 | (n) & (1ULL << 37) ? 37 : \ | |
113 | (n) & (1ULL << 36) ? 36 : \ | |
114 | (n) & (1ULL << 35) ? 35 : \ | |
115 | (n) & (1ULL << 34) ? 34 : \ | |
116 | (n) & (1ULL << 33) ? 33 : \ | |
117 | (n) & (1ULL << 32) ? 32 : \ | |
118 | (n) & (1ULL << 31) ? 31 : \ | |
119 | (n) & (1ULL << 30) ? 30 : \ | |
120 | (n) & (1ULL << 29) ? 29 : \ | |
121 | (n) & (1ULL << 28) ? 28 : \ | |
122 | (n) & (1ULL << 27) ? 27 : \ | |
123 | (n) & (1ULL << 26) ? 26 : \ | |
124 | (n) & (1ULL << 25) ? 25 : \ | |
125 | (n) & (1ULL << 24) ? 24 : \ | |
126 | (n) & (1ULL << 23) ? 23 : \ | |
127 | (n) & (1ULL << 22) ? 22 : \ | |
128 | (n) & (1ULL << 21) ? 21 : \ | |
129 | (n) & (1ULL << 20) ? 20 : \ | |
130 | (n) & (1ULL << 19) ? 19 : \ | |
131 | (n) & (1ULL << 18) ? 18 : \ | |
132 | (n) & (1ULL << 17) ? 17 : \ | |
133 | (n) & (1ULL << 16) ? 16 : \ | |
134 | (n) & (1ULL << 15) ? 15 : \ | |
135 | (n) & (1ULL << 14) ? 14 : \ | |
136 | (n) & (1ULL << 13) ? 13 : \ | |
137 | (n) & (1ULL << 12) ? 12 : \ | |
138 | (n) & (1ULL << 11) ? 11 : \ | |
139 | (n) & (1ULL << 10) ? 10 : \ | |
140 | (n) & (1ULL << 9) ? 9 : \ | |
141 | (n) & (1ULL << 8) ? 8 : \ | |
142 | (n) & (1ULL << 7) ? 7 : \ | |
143 | (n) & (1ULL << 6) ? 6 : \ | |
144 | (n) & (1ULL << 5) ? 5 : \ | |
145 | (n) & (1ULL << 4) ? 4 : \ | |
146 | (n) & (1ULL << 3) ? 3 : \ | |
147 | (n) & (1ULL << 2) ? 2 : \ | |
148 | (n) & (1ULL << 1) ? 1 : \ | |
149 | (n) & (1ULL << 0) ? 0 : \ | |
150 | ____ilog2_NaN() \ | |
151 | ) : \ | |
152 | (sizeof(n) <= 4) ? \ | |
153 | __ilog2_u32(n) : \ | |
154 | __ilog2_u64(n) \ | |
155 | ) | |
156 | ||
157 | /** | |
158 | * roundup_pow_of_two - round the given value up to nearest power of two | |
159 | * @n - parameter | |
160 | * | |
161 | * round the given value up to the nearest power of two | |
162 | * - the result is undefined when n == 0 | |
163 | * - this can be used to initialise global variables from constant data | |
164 | */ | |
165 | #define roundup_pow_of_two(n) \ | |
166 | ( \ | |
167 | __builtin_constant_p(n) ? ( \ | |
168 | (n == 1) ? 1 : \ | |
169 | (1UL << (ilog2((n) - 1) + 1)) \ | |
170 | ) : \ | |
171 | __roundup_pow_of_two(n) \ | |
172 | ) | |
173 | ||
174 | /** | |
175 | * rounddown_pow_of_two - round the given value down to nearest power of two | |
176 | * @n - parameter | |
177 | * | |
178 | * round the given value down to the nearest power of two | |
179 | * - the result is undefined when n == 0 | |
180 | * - this can be used to initialise global variables from constant data | |
181 | */ | |
182 | #define rounddown_pow_of_two(n) \ | |
183 | ( \ | |
184 | __builtin_constant_p(n) ? ( \ | |
185 | (1UL << ilog2(n))) : \ | |
186 | __rounddown_pow_of_two(n) \ | |
187 | ) | |
188 | ||
189 | /** | |
190 | * order_base_2 - calculate the (rounded up) base 2 order of the argument | |
191 | * @n: parameter | |
192 | * | |
193 | * The first few values calculated by this routine: | |
194 | * ob2(0) = 0 | |
195 | * ob2(1) = 0 | |
196 | * ob2(2) = 1 | |
197 | * ob2(3) = 2 | |
198 | * ob2(4) = 2 | |
199 | * ob2(5) = 3 | |
200 | * ... and so on. | |
201 | */ | |
202 | ||
203 | #define order_base_2(n) ilog2(roundup_pow_of_two(n)) | |
204 | ||
205 | #endif /* _LINUX_LOG2_H */ |