```   1/* SPDX-License-Identifier: GPL-2.0-or-later */
2/* Integer base 2 logarithm calculation
3 *
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
21static inline __attribute__((const))
22int __ilog2_u32(u32 n)
23{
24        return fls(n) - 1;
25}
26#endif
27
28#ifndef CONFIG_ARCH_HAS_ILOG2_U64
29static inline __attribute__((const))
30int __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 */
44static inline __attribute__((const))
45bool 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 */
54static inline __attribute__((const))
55unsigned long __roundup_pow_of_two(unsigned long n)
56{
57        return 1UL << fls_long(n - 1);
58}
59
60/**
61 * __rounddown_pow_of_two() - round down to nearest power of two
62 * @n: value to round down
63 */
64static inline __attribute__((const))
65unsigned long __rounddown_pow_of_two(unsigned long n)
66{
67        return 1UL << (fls_long(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        const_ilog2(n) :                \
160        (sizeof(n) <= 4) ?              \
161        __ilog2_u32(n) :                \
162        __ilog2_u64(n)                  \
163 )
164
165/**
166 * roundup_pow_of_two - round the given value up to nearest power of two
167 * @n: parameter
168 *
169 * round the given value up to the nearest power of two
170 * - the result is undefined when n == 0
171 * - this can be used to initialise global variables from constant data
172 */
173#define roundup_pow_of_two(n)                   \
174(                                               \
175        __builtin_constant_p(n) ? (             \
176                (n == 1) ? 1 :                  \
177                (1UL << (ilog2((n) - 1) + 1))   \
178                                   ) :          \
179        __roundup_pow_of_two(n)                 \
180 )
181
182/**
183 * rounddown_pow_of_two - round the given value down to nearest power of two
184 * @n: parameter
185 *
186 * round the given value down to the nearest power of two
187 * - the result is undefined when n == 0
188 * - this can be used to initialise global variables from constant data
189 */
190#define rounddown_pow_of_two(n)                 \
191(                                               \
192        __builtin_constant_p(n) ? (             \
193                (1UL << ilog2(n))) :            \
194        __rounddown_pow_of_two(n)               \
195 )
196
197static inline __attribute_const__
198int __order_base_2(unsigned long n)
199{
200        return n > 1 ? ilog2(n - 1) + 1 : 0;
201}
202
203/**
204 * order_base_2 - calculate the (rounded up) base 2 order of the argument
205 * @n: parameter
206 *
207 * The first few values calculated by this routine:
208 *  ob2(0) = 0
209 *  ob2(1) = 0
210 *  ob2(2) = 1
211 *  ob2(3) = 2
212 *  ob2(4) = 2
213 *  ob2(5) = 3
214 *  ... and so on.
215 */
216#define order_base_2(n)                         \
217(                                               \
218        __builtin_constant_p(n) ? (             \
219                ((n) == 0 || (n) == 1) ? 0 :    \
220                ilog2((n) - 1) + 1) :           \
221        __order_base_2(n)                       \
222)
223
224static inline __attribute__((const))
225int __bits_per(unsigned long n)
226{
227        if (n < 2)
228                return 1;
229        if (is_power_of_2(n))
230                return order_base_2(n) + 1;
231        return order_base_2(n);
232}
233
234/**
235 * bits_per - calculate the number of bits required for the argument
236 * @n: parameter
237 *
238 * This is constant-capable and can be used for compile time
239 * initializations, e.g bitfields.
240 *
241 * The first few values calculated by this routine:
242 * bf(0) = 1
243 * bf(1) = 1
244 * bf(2) = 2
245 * bf(3) = 2
246 * bf(4) = 3
247 * ... and so on.
248 */
249#define bits_per(n)                             \
250(                                               \
251        __builtin_constant_p(n) ? (             \
252                ((n) == 0 || (n) == 1)          \
253                        ? 1 : ilog2(n) + 1      \
254        ) :                                     \
255        __bits_per(n)                           \
256)
257#endif /* _LINUX_LOG2_H */
258```