xref: /openbmc/linux/include/linux/log2.h (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 extern __attribute__((const, noreturn))
22 int ____ilog2_NaN(void);
23 
24 /*
25  * non-constant log of base 2 calculators
26  * - the arch may override these in asm/bitops.h if they can be implemented
27  *   more efficiently than using fls() and fls64()
28  * - the arch is not required to handle n==0 if implementing the fallback
29  */
30 #ifndef CONFIG_ARCH_HAS_ILOG2_U32
31 static inline __attribute__((const))
32 int __ilog2_u32(u32 n)
33 {
34 	return fls(n) - 1;
35 }
36 #endif
37 
38 #ifndef CONFIG_ARCH_HAS_ILOG2_U64
39 static inline __attribute__((const))
40 int __ilog2_u64(u64 n)
41 {
42 	return fls64(n) - 1;
43 }
44 #endif
45 
46 /*
47  *  Determine whether some value is a power of two, where zero is
48  * *not* considered a power of two.
49  */
50 
51 static inline __attribute__((const))
52 bool is_power_of_2(unsigned long n)
53 {
54 	return (n != 0 && ((n & (n - 1)) == 0));
55 }
56 
57 /*
58  * round up to nearest power of two
59  */
60 static inline __attribute__((const))
61 unsigned long __roundup_pow_of_two(unsigned long n)
62 {
63 	return 1UL << fls_long(n - 1);
64 }
65 
66 /**
67  * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
68  * @n - parameter
69  *
70  * constant-capable log of base 2 calculation
71  * - this can be used to initialise global variables from constant data, hence
72  *   the massive ternary operator construction
73  *
74  * selects the appropriately-sized optimised version depending on sizeof(n)
75  */
76 #define ilog2(n)				\
77 (						\
78 	__builtin_constant_p(n) ? (		\
79 		(n) < 1 ? ____ilog2_NaN() :	\
80 		(n) & (1ULL << 63) ? 63 :	\
81 		(n) & (1ULL << 62) ? 62 :	\
82 		(n) & (1ULL << 61) ? 61 :	\
83 		(n) & (1ULL << 60) ? 60 :	\
84 		(n) & (1ULL << 59) ? 59 :	\
85 		(n) & (1ULL << 58) ? 58 :	\
86 		(n) & (1ULL << 57) ? 57 :	\
87 		(n) & (1ULL << 56) ? 56 :	\
88 		(n) & (1ULL << 55) ? 55 :	\
89 		(n) & (1ULL << 54) ? 54 :	\
90 		(n) & (1ULL << 53) ? 53 :	\
91 		(n) & (1ULL << 52) ? 52 :	\
92 		(n) & (1ULL << 51) ? 51 :	\
93 		(n) & (1ULL << 50) ? 50 :	\
94 		(n) & (1ULL << 49) ? 49 :	\
95 		(n) & (1ULL << 48) ? 48 :	\
96 		(n) & (1ULL << 47) ? 47 :	\
97 		(n) & (1ULL << 46) ? 46 :	\
98 		(n) & (1ULL << 45) ? 45 :	\
99 		(n) & (1ULL << 44) ? 44 :	\
100 		(n) & (1ULL << 43) ? 43 :	\
101 		(n) & (1ULL << 42) ? 42 :	\
102 		(n) & (1ULL << 41) ? 41 :	\
103 		(n) & (1ULL << 40) ? 40 :	\
104 		(n) & (1ULL << 39) ? 39 :	\
105 		(n) & (1ULL << 38) ? 38 :	\
106 		(n) & (1ULL << 37) ? 37 :	\
107 		(n) & (1ULL << 36) ? 36 :	\
108 		(n) & (1ULL << 35) ? 35 :	\
109 		(n) & (1ULL << 34) ? 34 :	\
110 		(n) & (1ULL << 33) ? 33 :	\
111 		(n) & (1ULL << 32) ? 32 :	\
112 		(n) & (1ULL << 31) ? 31 :	\
113 		(n) & (1ULL << 30) ? 30 :	\
114 		(n) & (1ULL << 29) ? 29 :	\
115 		(n) & (1ULL << 28) ? 28 :	\
116 		(n) & (1ULL << 27) ? 27 :	\
117 		(n) & (1ULL << 26) ? 26 :	\
118 		(n) & (1ULL << 25) ? 25 :	\
119 		(n) & (1ULL << 24) ? 24 :	\
120 		(n) & (1ULL << 23) ? 23 :	\
121 		(n) & (1ULL << 22) ? 22 :	\
122 		(n) & (1ULL << 21) ? 21 :	\
123 		(n) & (1ULL << 20) ? 20 :	\
124 		(n) & (1ULL << 19) ? 19 :	\
125 		(n) & (1ULL << 18) ? 18 :	\
126 		(n) & (1ULL << 17) ? 17 :	\
127 		(n) & (1ULL << 16) ? 16 :	\
128 		(n) & (1ULL << 15) ? 15 :	\
129 		(n) & (1ULL << 14) ? 14 :	\
130 		(n) & (1ULL << 13) ? 13 :	\
131 		(n) & (1ULL << 12) ? 12 :	\
132 		(n) & (1ULL << 11) ? 11 :	\
133 		(n) & (1ULL << 10) ? 10 :	\
134 		(n) & (1ULL <<  9) ?  9 :	\
135 		(n) & (1ULL <<  8) ?  8 :	\
136 		(n) & (1ULL <<  7) ?  7 :	\
137 		(n) & (1ULL <<  6) ?  6 :	\
138 		(n) & (1ULL <<  5) ?  5 :	\
139 		(n) & (1ULL <<  4) ?  4 :	\
140 		(n) & (1ULL <<  3) ?  3 :	\
141 		(n) & (1ULL <<  2) ?  2 :	\
142 		(n) & (1ULL <<  1) ?  1 :	\
143 		(n) & (1ULL <<  0) ?  0 :	\
144 		____ilog2_NaN()			\
145 				   ) :		\
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) ? 0 :			\
163 		(1UL << (ilog2((n) - 1) + 1))	\
164 				   ) :		\
165 	__roundup_pow_of_two(n)			\
166  )
167 
168 #endif /* _LINUX_LOG2_H */
169