ReactOS  0.4.14-dev-614-gbfd8a84
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  * deal with unrepresentable constant logarithms
20  */
21 int ____ilog2_NaN(void);
22 
23 /*
24  * non-constant log of base 2 calculators
25  * - the arch may override these in asm/bitops.h if they can be implemented
26  * more efficiently than using fls() and fls64()
27  * - the arch is not required to handle n==0 if implementing the fallback
28  */
29 #ifndef CONFIG_ARCH_HAS_ILOG2_U32
30 static inline __attribute__((const))
31 int __ilog2_u32(u32 n)
32 {
33  return fls(n) - 1;
34 }
35 #endif
36 
37 #ifndef CONFIG_ARCH_HAS_ILOG2_U64
38 static inline __attribute__((const))
39 int __ilog2_u64(u64 n)
40 {
41  return fls64(n) - 1;
42 }
43 #endif
44 
45 /*
46  * Determine whether some value is a power of two, where zero is
47  * *not* considered a power of two.
48  */
49 
50 static inline __attribute__((const))
51 bool is_power_of_2(unsigned long n)
52 {
53  return (n != 0 && ((n & (n - 1)) == 0));
54 }
55 
56 /*
57  * round up to nearest power of two
58  */
59 static inline __attribute__((const))
60 unsigned long __roundup_pow_of_two(unsigned long n)
61 {
62  return 1UL << fls_long(n - 1);
63 }
64 
65 /*
66  * round down to nearest power of two
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 
84 #define ilog2(n) \
85 ( \
86  __builtin_constant_p(n) ? ( \
87  (n) < 1 ? ____ilog2_NaN() : \
88  (n) & (1ULL << 63) ? 63 : \
89  (n) & (1ULL << 62) ? 62 : \
90  (n) & (1ULL << 61) ? 61 : \
91  (n) & (1ULL << 60) ? 60 : \
92  (n) & (1ULL << 59) ? 59 : \
93  (n) & (1ULL << 58) ? 58 : \
94  (n) & (1ULL << 57) ? 57 : \
95  (n) & (1ULL << 56) ? 56 : \
96  (n) & (1ULL << 55) ? 55 : \
97  (n) & (1ULL << 54) ? 54 : \
98  (n) & (1ULL << 53) ? 53 : \
99  (n) & (1ULL << 52) ? 52 : \
100  (n) & (1ULL << 51) ? 51 : \
101  (n) & (1ULL << 50) ? 50 : \
102  (n) & (1ULL << 49) ? 49 : \
103  (n) & (1ULL << 48) ? 48 : \
104  (n) & (1ULL << 47) ? 47 : \
105  (n) & (1ULL << 46) ? 46 : \
106  (n) & (1ULL << 45) ? 45 : \
107  (n) & (1ULL << 44) ? 44 : \
108  (n) & (1ULL << 43) ? 43 : \
109  (n) & (1ULL << 42) ? 42 : \
110  (n) & (1ULL << 41) ? 41 : \
111  (n) & (1ULL << 40) ? 40 : \
112  (n) & (1ULL << 39) ? 39 : \
113  (n) & (1ULL << 38) ? 38 : \
114  (n) & (1ULL << 37) ? 37 : \
115  (n) & (1ULL << 36) ? 36 : \
116  (n) & (1ULL << 35) ? 35 : \
117  (n) & (1ULL << 34) ? 34 : \
118  (n) & (1ULL << 33) ? 33 : \
119  (n) & (1ULL << 32) ? 32 : \
120  (n) & (1ULL << 31) ? 31 : \
121  (n) & (1ULL << 30) ? 30 : \
122  (n) & (1ULL << 29) ? 29 : \
123  (n) & (1ULL << 28) ? 28 : \
124  (n) & (1ULL << 27) ? 27 : \
125  (n) & (1ULL << 26) ? 26 : \
126  (n) & (1ULL << 25) ? 25 : \
127  (n) & (1ULL << 24) ? 24 : \
128  (n) & (1ULL << 23) ? 23 : \
129  (n) & (1ULL << 22) ? 22 : \
130  (n) & (1ULL << 21) ? 21 : \
131  (n) & (1ULL << 20) ? 20 : \
132  (n) & (1ULL << 19) ? 19 : \
133  (n) & (1ULL << 18) ? 18 : \
134  (n) & (1ULL << 17) ? 17 : \
135  (n) & (1ULL << 16) ? 16 : \
136  (n) & (1ULL << 15) ? 15 : \
137  (n) & (1ULL << 14) ? 14 : \
138  (n) & (1ULL << 13) ? 13 : \
139  (n) & (1ULL << 12) ? 12 : \
140  (n) & (1ULL << 11) ? 11 : \
141  (n) & (1ULL << 10) ? 10 : \
142  (n) & (1ULL << 9) ? 9 : \
143  (n) & (1ULL << 8) ? 8 : \
144  (n) & (1ULL << 7) ? 7 : \
145  (n) & (1ULL << 6) ? 6 : \
146  (n) & (1ULL << 5) ? 5 : \
147  (n) & (1ULL << 4) ? 4 : \
148  (n) & (1ULL << 3) ? 3 : \
149  (n) & (1ULL << 2) ? 2 : \
150  (n) & (1ULL << 1) ? 1 : \
151  (n) & (1ULL << 0) ? 0 : \
152  ____ilog2_NaN() \
153  ) : \
154  (sizeof(n) <= 4) ? \
155  __ilog2_u32(n) : \
156  __ilog2_u64(n) \
157  )
158 
167 #define roundup_pow_of_two(n) \
168 ( \
169  __builtin_constant_p(n) ? ( \
170  (n == 1) ? 1 : \
171  (1UL << (ilog2((n) - 1) + 1)) \
172  ) : \
173  __roundup_pow_of_two(n) \
174  )
175 
184 #define rounddown_pow_of_two(n) \
185 ( \
186  __builtin_constant_p(n) ? ( \
187  (n == 1) ? 0 : \
188  (1UL << ilog2(n))) : \
189  __rounddown_pow_of_two(n) \
190  )
191 
206 #define order_base_2(n) ilog2(roundup_pow_of_two(n))
207 
208 #endif /* _LINUX_LOG2_H */
#define is_power_of_2(x)
Definition: memory.c:2294
static int fls64(__u64 x)
Definition: bitops.h:186
GLdouble n
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ULONG32 u32
Definition: btrfs.h:14
int ____ilog2_NaN(void)
static int fls(int x)
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ULONG64 u64
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static __attribute__((const)) int __ilog2_u32(u32 n)
Definition: log2.h:30
static unsigned fls_long(unsigned long l)
Definition: bitops.h:239
#define UL
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