1 | /* SPDX-License-Identifier: GPL-2.0-or-later */ |
2 | /* Integer base 2 logarithm calculation |
3 | * |
4 | * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. |
5 | * Written by David Howells (dhowells@redhat.com) |
6 | */ |
7 | |
8 | #ifndef _LINUX_LOG2_H |
9 | #define _LINUX_LOG2_H |
10 | |
11 | #include <linux/types.h> |
12 | #include <linux/bitops.h> |
13 | |
14 | /* |
15 | * non-constant log of base 2 calculators |
16 | * - the arch may override these in asm/bitops.h if they can be implemented |
17 | * more efficiently than using fls() and fls64() |
18 | * - the arch is not required to handle n==0 if implementing the fallback |
19 | */ |
20 | #ifndef CONFIG_ARCH_HAS_ILOG2_U32 |
21 | static __always_inline __attribute__((const)) |
22 | int __ilog2_u32(u32 n) |
23 | { |
24 | return fls(n) - 1; |
25 | } |
26 | #endif |
27 | |
28 | #ifndef CONFIG_ARCH_HAS_ILOG2_U64 |
29 | static __always_inline __attribute__((const)) |
30 | int __ilog2_u64(u64 n) |
31 | { |
32 | return fls64(n) - 1; |
33 | } |
34 | #endif |
35 | |
36 | /** |
37 | * is_power_of_2() - check if a value is a power of two |
38 | * @n: the value to check |
39 | * |
40 | * Determine whether some value is a power of two, where zero is |
41 | * *not* considered a power of two. |
42 | * Return: true if @n is a power of 2, otherwise false. |
43 | */ |
44 | static inline __attribute__((const)) |
45 | bool is_power_of_2(unsigned long n) |
46 | { |
47 | return (n != 0 && ((n & (n - 1)) == 0)); |
48 | } |
49 | |
50 | /** |
51 | * __roundup_pow_of_two() - round up to nearest power of two |
52 | * @n: value to round up |
53 | */ |
54 | static inline __attribute__((const)) |
55 | unsigned long __roundup_pow_of_two(unsigned long n) |
56 | { |
57 | return 1UL << fls_long(l: n - 1); |
58 | } |
59 | |
60 | /** |
61 | * __rounddown_pow_of_two() - round down to nearest power of two |
62 | * @n: value to round down |
63 | */ |
64 | static inline __attribute__((const)) |
65 | unsigned long __rounddown_pow_of_two(unsigned long n) |
66 | { |
67 | return 1UL << (fls_long(l: n) - 1); |
68 | } |
69 | |
70 | /** |
71 | * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value |
72 | * @n: parameter |
73 | * |
74 | * Use this where sparse expects a true constant expression, e.g. for array |
75 | * indices. |
76 | */ |
77 | #define const_ilog2(n) \ |
78 | ( \ |
79 | __builtin_constant_p(n) ? ( \ |
80 | (n) < 2 ? 0 : \ |
81 | (n) & (1ULL << 63) ? 63 : \ |
82 | (n) & (1ULL << 62) ? 62 : \ |
83 | (n) & (1ULL << 61) ? 61 : \ |
84 | (n) & (1ULL << 60) ? 60 : \ |
85 | (n) & (1ULL << 59) ? 59 : \ |
86 | (n) & (1ULL << 58) ? 58 : \ |
87 | (n) & (1ULL << 57) ? 57 : \ |
88 | (n) & (1ULL << 56) ? 56 : \ |
89 | (n) & (1ULL << 55) ? 55 : \ |
90 | (n) & (1ULL << 54) ? 54 : \ |
91 | (n) & (1ULL << 53) ? 53 : \ |
92 | (n) & (1ULL << 52) ? 52 : \ |
93 | (n) & (1ULL << 51) ? 51 : \ |
94 | (n) & (1ULL << 50) ? 50 : \ |
95 | (n) & (1ULL << 49) ? 49 : \ |
96 | (n) & (1ULL << 48) ? 48 : \ |
97 | (n) & (1ULL << 47) ? 47 : \ |
98 | (n) & (1ULL << 46) ? 46 : \ |
99 | (n) & (1ULL << 45) ? 45 : \ |
100 | (n) & (1ULL << 44) ? 44 : \ |
101 | (n) & (1ULL << 43) ? 43 : \ |
102 | (n) & (1ULL << 42) ? 42 : \ |
103 | (n) & (1ULL << 41) ? 41 : \ |
104 | (n) & (1ULL << 40) ? 40 : \ |
105 | (n) & (1ULL << 39) ? 39 : \ |
106 | (n) & (1ULL << 38) ? 38 : \ |
107 | (n) & (1ULL << 37) ? 37 : \ |
108 | (n) & (1ULL << 36) ? 36 : \ |
109 | (n) & (1ULL << 35) ? 35 : \ |
110 | (n) & (1ULL << 34) ? 34 : \ |
111 | (n) & (1ULL << 33) ? 33 : \ |
112 | (n) & (1ULL << 32) ? 32 : \ |
113 | (n) & (1ULL << 31) ? 31 : \ |
114 | (n) & (1ULL << 30) ? 30 : \ |
115 | (n) & (1ULL << 29) ? 29 : \ |
116 | (n) & (1ULL << 28) ? 28 : \ |
117 | (n) & (1ULL << 27) ? 27 : \ |
118 | (n) & (1ULL << 26) ? 26 : \ |
119 | (n) & (1ULL << 25) ? 25 : \ |
120 | (n) & (1ULL << 24) ? 24 : \ |
121 | (n) & (1ULL << 23) ? 23 : \ |
122 | (n) & (1ULL << 22) ? 22 : \ |
123 | (n) & (1ULL << 21) ? 21 : \ |
124 | (n) & (1ULL << 20) ? 20 : \ |
125 | (n) & (1ULL << 19) ? 19 : \ |
126 | (n) & (1ULL << 18) ? 18 : \ |
127 | (n) & (1ULL << 17) ? 17 : \ |
128 | (n) & (1ULL << 16) ? 16 : \ |
129 | (n) & (1ULL << 15) ? 15 : \ |
130 | (n) & (1ULL << 14) ? 14 : \ |
131 | (n) & (1ULL << 13) ? 13 : \ |
132 | (n) & (1ULL << 12) ? 12 : \ |
133 | (n) & (1ULL << 11) ? 11 : \ |
134 | (n) & (1ULL << 10) ? 10 : \ |
135 | (n) & (1ULL << 9) ? 9 : \ |
136 | (n) & (1ULL << 8) ? 8 : \ |
137 | (n) & (1ULL << 7) ? 7 : \ |
138 | (n) & (1ULL << 6) ? 6 : \ |
139 | (n) & (1ULL << 5) ? 5 : \ |
140 | (n) & (1ULL << 4) ? 4 : \ |
141 | (n) & (1ULL << 3) ? 3 : \ |
142 | (n) & (1ULL << 2) ? 2 : \ |
143 | 1) : \ |
144 | -1) |
145 | |
146 | /** |
147 | * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value |
148 | * @n: parameter |
149 | * |
150 | * constant-capable log of base 2 calculation |
151 | * - this can be used to initialise global variables from constant data, hence |
152 | * the massive ternary operator construction |
153 | * |
154 | * selects the appropriately-sized optimised version depending on sizeof(n) |
155 | */ |
156 | #define ilog2(n) \ |
157 | ( \ |
158 | __builtin_constant_p(n) ? \ |
159 | ((n) < 2 ? 0 : \ |
160 | 63 - __builtin_clzll(n)) : \ |
161 | (sizeof(n) <= 4) ? \ |
162 | __ilog2_u32(n) : \ |
163 | __ilog2_u64(n) \ |
164 | ) |
165 | |
166 | /** |
167 | * roundup_pow_of_two - round the given value up to nearest power of two |
168 | * @n: parameter |
169 | * |
170 | * round the given value up to the nearest power of two |
171 | * - the result is undefined when n == 0 |
172 | * - this can be used to initialise global variables from constant data |
173 | */ |
174 | #define roundup_pow_of_two(n) \ |
175 | ( \ |
176 | __builtin_constant_p(n) ? ( \ |
177 | ((n) == 1) ? 1 : \ |
178 | (1UL << (ilog2((n) - 1) + 1)) \ |
179 | ) : \ |
180 | __roundup_pow_of_two(n) \ |
181 | ) |
182 | |
183 | /** |
184 | * rounddown_pow_of_two - round the given value down to nearest power of two |
185 | * @n: parameter |
186 | * |
187 | * round the given value down to the nearest power of two |
188 | * - the result is undefined when n == 0 |
189 | * - this can be used to initialise global variables from constant data |
190 | */ |
191 | #define rounddown_pow_of_two(n) \ |
192 | ( \ |
193 | __builtin_constant_p(n) ? ( \ |
194 | (1UL << ilog2(n))) : \ |
195 | __rounddown_pow_of_two(n) \ |
196 | ) |
197 | |
198 | static inline __attribute_const__ |
199 | int __order_base_2(unsigned long n) |
200 | { |
201 | return n > 1 ? ilog2(n - 1) + 1 : 0; |
202 | } |
203 | |
204 | /** |
205 | * order_base_2 - calculate the (rounded up) base 2 order of the argument |
206 | * @n: parameter |
207 | * |
208 | * The first few values calculated by this routine: |
209 | * ob2(0) = 0 |
210 | * ob2(1) = 0 |
211 | * ob2(2) = 1 |
212 | * ob2(3) = 2 |
213 | * ob2(4) = 2 |
214 | * ob2(5) = 3 |
215 | * ... and so on. |
216 | */ |
217 | #define order_base_2(n) \ |
218 | ( \ |
219 | __builtin_constant_p(n) ? ( \ |
220 | ((n) == 0 || (n) == 1) ? 0 : \ |
221 | ilog2((n) - 1) + 1) : \ |
222 | __order_base_2(n) \ |
223 | ) |
224 | |
225 | static inline __attribute__((const)) |
226 | int __bits_per(unsigned long n) |
227 | { |
228 | if (n < 2) |
229 | return 1; |
230 | if (is_power_of_2(n)) |
231 | return order_base_2(n) + 1; |
232 | return order_base_2(n); |
233 | } |
234 | |
235 | /** |
236 | * bits_per - calculate the number of bits required for the argument |
237 | * @n: parameter |
238 | * |
239 | * This is constant-capable and can be used for compile time |
240 | * initializations, e.g bitfields. |
241 | * |
242 | * The first few values calculated by this routine: |
243 | * bf(0) = 1 |
244 | * bf(1) = 1 |
245 | * bf(2) = 2 |
246 | * bf(3) = 2 |
247 | * bf(4) = 3 |
248 | * ... and so on. |
249 | */ |
250 | #define bits_per(n) \ |
251 | ( \ |
252 | __builtin_constant_p(n) ? ( \ |
253 | ((n) == 0 || (n) == 1) \ |
254 | ? 1 : ilog2(n) + 1 \ |
255 | ) : \ |
256 | __bits_per(n) \ |
257 | ) |
258 | #endif /* _LINUX_LOG2_H */ |
259 | |