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TOMOYO Linux Cross Reference
Linux/include/linux/log2.h

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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  * 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 
 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 
 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
 45  * *not* considered a power of two.
 46  * Return: true if @n is a power of 2, otherwise false.
 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  * __roundup_pow_of_two() - round up to nearest power of two
 56  * @n: value to round up
 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 
 64 /**
 65  * __rounddown_pow_of_two() - round down to nearest power of two
 66  * @n: value to round down
 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 
 74 /**
 75  * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value
 76  * @n: parameter
 77  *
 78  * Use this where sparse expects a true constant expression, e.g. for array
 79  * indices.
 80  */
 81 #define const_ilog2(n)                          \
 82 (                                               \
 83         __builtin_constant_p(n) ? (             \
 84                 (n) < 2 ? 0 :                   \
 85                 (n) & (1ULL << 63) ? 63 :       \
 86                 (n) & (1ULL << 62) ? 62 :       \
 87                 (n) & (1ULL << 61) ? 61 :       \
 88                 (n) & (1ULL << 60) ? 60 :       \
 89                 (n) & (1ULL << 59) ? 59 :       \
 90                 (n) & (1ULL << 58) ? 58 :       \
 91                 (n) & (1ULL << 57) ? 57 :       \
 92                 (n) & (1ULL << 56) ? 56 :       \
 93                 (n) & (1ULL << 55) ? 55 :       \
 94                 (n) & (1ULL << 54) ? 54 :       \
 95                 (n) & (1ULL << 53) ? 53 :       \
 96                 (n) & (1ULL << 52) ? 52 :       \
 97                 (n) & (1ULL << 51) ? 51 :       \
 98                 (n) & (1ULL << 50) ? 50 :       \
 99                 (n) & (1ULL << 49) ? 49 :       \
100                 (n) & (1ULL << 48) ? 48 :       \
101                 (n) & (1ULL << 47) ? 47 :       \
102                 (n) & (1ULL << 46) ? 46 :       \
103                 (n) & (1ULL << 45) ? 45 :       \
104                 (n) & (1ULL << 44) ? 44 :       \
105                 (n) & (1ULL << 43) ? 43 :       \
106                 (n) & (1ULL << 42) ? 42 :       \
107                 (n) & (1ULL << 41) ? 41 :       \
108                 (n) & (1ULL << 40) ? 40 :       \
109                 (n) & (1ULL << 39) ? 39 :       \
110                 (n) & (1ULL << 38) ? 38 :       \
111                 (n) & (1ULL << 37) ? 37 :       \
112                 (n) & (1ULL << 36) ? 36 :       \
113                 (n) & (1ULL << 35) ? 35 :       \
114                 (n) & (1ULL << 34) ? 34 :       \
115                 (n) & (1ULL << 33) ? 33 :       \
116                 (n) & (1ULL << 32) ? 32 :       \
117                 (n) & (1ULL << 31) ? 31 :       \
118                 (n) & (1ULL << 30) ? 30 :       \
119                 (n) & (1ULL << 29) ? 29 :       \
120                 (n) & (1ULL << 28) ? 28 :       \
121                 (n) & (1ULL << 27) ? 27 :       \
122                 (n) & (1ULL << 26) ? 26 :       \
123                 (n) & (1ULL << 25) ? 25 :       \
124                 (n) & (1ULL << 24) ? 24 :       \
125                 (n) & (1ULL << 23) ? 23 :       \
126                 (n) & (1ULL << 22) ? 22 :       \
127                 (n) & (1ULL << 21) ? 21 :       \
128                 (n) & (1ULL << 20) ? 20 :       \
129                 (n) & (1ULL << 19) ? 19 :       \
130                 (n) & (1ULL << 18) ? 18 :       \
131                 (n) & (1ULL << 17) ? 17 :       \
132                 (n) & (1ULL << 16) ? 16 :       \
133                 (n) & (1ULL << 15) ? 15 :       \
134                 (n) & (1ULL << 14) ? 14 :       \
135                 (n) & (1ULL << 13) ? 13 :       \
136                 (n) & (1ULL << 12) ? 12 :       \
137                 (n) & (1ULL << 11) ? 11 :       \
138                 (n) & (1ULL << 10) ? 10 :       \
139                 (n) & (1ULL <<  9) ?  9 :       \
140                 (n) & (1ULL <<  8) ?  8 :       \
141                 (n) & (1ULL <<  7) ?  7 :       \
142                 (n) & (1ULL <<  6) ?  6 :       \
143                 (n) & (1ULL <<  5) ?  5 :       \
144                 (n) & (1ULL <<  4) ?  4 :       \
145                 (n) & (1ULL <<  3) ?  3 :       \
146                 (n) & (1ULL <<  2) ?  2 :       \
147                 1) :                            \
148         -1)
149 
150 /**
151  * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value
152  * @n: parameter
153  *
154  * constant-capable log of base 2 calculation
155  * - this can be used to initialise global variables from constant data, hence
156  * the massive ternary operator construction
157  *
158  * selects the appropriately-sized optimised version depending on sizeof(n)
159  */
160 #define ilog2(n) \
161 ( \
162         __builtin_constant_p(n) ?       \
163         const_ilog2(n) :                \
164         (sizeof(n) <= 4) ?              \
165         __ilog2_u32(n) :                \
166         __ilog2_u64(n)                  \
167  )
168 
169 /**
170  * roundup_pow_of_two - round the given value up to nearest power of two
171  * @n: parameter
172  *
173  * round the given value up to the nearest power of two
174  * - the result is undefined when n == 0
175  * - this can be used to initialise global variables from constant data
176  */
177 #define roundup_pow_of_two(n)                   \
178 (                                               \
179         __builtin_constant_p(n) ? (             \
180                 (n == 1) ? 1 :                  \
181                 (1UL << (ilog2((n) - 1) + 1))   \
182                                    ) :          \
183         __roundup_pow_of_two(n)                 \
184  )
185 
186 /**
187  * rounddown_pow_of_two - round the given value down to nearest power of two
188  * @n: parameter
189  *
190  * round the given value down to the nearest power of two
191  * - the result is undefined when n == 0
192  * - this can be used to initialise global variables from constant data
193  */
194 #define rounddown_pow_of_two(n)                 \
195 (                                               \
196         __builtin_constant_p(n) ? (             \
197                 (1UL << ilog2(n))) :            \
198         __rounddown_pow_of_two(n)               \
199  )
200 
201 static inline __attribute_const__
202 int __order_base_2(unsigned long n)
203 {
204         return n > 1 ? ilog2(n - 1) + 1 : 0;
205 }
206 
207 /**
208  * order_base_2 - calculate the (rounded up) base 2 order of the argument
209  * @n: parameter
210  *
211  * The first few values calculated by this routine:
212  *  ob2(0) = 0
213  *  ob2(1) = 0
214  *  ob2(2) = 1
215  *  ob2(3) = 2
216  *  ob2(4) = 2
217  *  ob2(5) = 3
218  *  ... and so on.
219  */
220 #define order_base_2(n)                         \
221 (                                               \
222         __builtin_constant_p(n) ? (             \
223                 ((n) == 0 || (n) == 1) ? 0 :    \
224                 ilog2((n) - 1) + 1) :           \
225         __order_base_2(n)                       \
226 )
227 #endif /* _LINUX_LOG2_H */
228 

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