~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

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

Version: ~ [ linux-5.9-rc5 ] ~ [ linux-5.8.10 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.66 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.146 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.198 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.236 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.236 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.140 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.85 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

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

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp