xref: /openbmc/u-boot/include/linux/log2.h (revision aefb8f4c)
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  * SPDX-License-Identifier:	GPL-2.0+
7  */
8 
9 #ifndef _LINUX_LOG2_H
10 #define _LINUX_LOG2_H
11 
12 #include <linux/types.h>
13 #include <linux/bitops.h>
14 
15 /*
16  * deal with unrepresentable constant logarithms
17  */
18 extern __attribute__((const, noreturn))
19 int ____ilog2_NaN(void);
20 
21 /*
22  * non-constant log of base 2 calculators
23  * - the arch may override these in asm/bitops.h if they can be implemented
24  *   more efficiently than using fls() and fls64()
25  * - the arch is not required to handle n==0 if implementing the fallback
26  */
27 #ifndef CONFIG_ARCH_HAS_ILOG2_U32
28 static inline __attribute__((const))
29 int __ilog2_u32(u32 n)
30 {
31 	return fls(n) - 1;
32 }
33 #endif
34 
35 #ifndef CONFIG_ARCH_HAS_ILOG2_U64
36 static inline __attribute__((const))
37 int __ilog2_u64(u64 n)
38 {
39 	return fls64(n) - 1;
40 }
41 #endif
42 
43 /*
44  *  Determine whether some value is a power of two, where zero is
45  * *not* considered a power of two.
46  */
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  * round up to nearest power of two
56  */
57 static inline __attribute__((const))
58 unsigned long __roundup_pow_of_two(unsigned long n)
59 {
60 	return 1UL << fls_long(n - 1);
61 }
62 
63 /*
64  * round down to nearest power of two
65  */
66 static inline __attribute__((const))
67 unsigned long __rounddown_pow_of_two(unsigned long n)
68 {
69 	return 1UL << (fls_long(n) - 1);
70 }
71 
72 /**
73  * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
74  * @n - parameter
75  *
76  * constant-capable log of base 2 calculation
77  * - this can be used to initialise global variables from constant data, hence
78  *   the massive ternary operator construction
79  *
80  * selects the appropriately-sized optimised version depending on sizeof(n)
81  */
82 #define ilog2(n)				\
83 (						\
84 	__builtin_constant_p(n) ? (		\
85 		(n) < 1 ? ____ilog2_NaN() :	\
86 		(n) & (1ULL << 63) ? 63 :	\
87 		(n) & (1ULL << 62) ? 62 :	\
88 		(n) & (1ULL << 61) ? 61 :	\
89 		(n) & (1ULL << 60) ? 60 :	\
90 		(n) & (1ULL << 59) ? 59 :	\
91 		(n) & (1ULL << 58) ? 58 :	\
92 		(n) & (1ULL << 57) ? 57 :	\
93 		(n) & (1ULL << 56) ? 56 :	\
94 		(n) & (1ULL << 55) ? 55 :	\
95 		(n) & (1ULL << 54) ? 54 :	\
96 		(n) & (1ULL << 53) ? 53 :	\
97 		(n) & (1ULL << 52) ? 52 :	\
98 		(n) & (1ULL << 51) ? 51 :	\
99 		(n) & (1ULL << 50) ? 50 :	\
100 		(n) & (1ULL << 49) ? 49 :	\
101 		(n) & (1ULL << 48) ? 48 :	\
102 		(n) & (1ULL << 47) ? 47 :	\
103 		(n) & (1ULL << 46) ? 46 :	\
104 		(n) & (1ULL << 45) ? 45 :	\
105 		(n) & (1ULL << 44) ? 44 :	\
106 		(n) & (1ULL << 43) ? 43 :	\
107 		(n) & (1ULL << 42) ? 42 :	\
108 		(n) & (1ULL << 41) ? 41 :	\
109 		(n) & (1ULL << 40) ? 40 :	\
110 		(n) & (1ULL << 39) ? 39 :	\
111 		(n) & (1ULL << 38) ? 38 :	\
112 		(n) & (1ULL << 37) ? 37 :	\
113 		(n) & (1ULL << 36) ? 36 :	\
114 		(n) & (1ULL << 35) ? 35 :	\
115 		(n) & (1ULL << 34) ? 34 :	\
116 		(n) & (1ULL << 33) ? 33 :	\
117 		(n) & (1ULL << 32) ? 32 :	\
118 		(n) & (1ULL << 31) ? 31 :	\
119 		(n) & (1ULL << 30) ? 30 :	\
120 		(n) & (1ULL << 29) ? 29 :	\
121 		(n) & (1ULL << 28) ? 28 :	\
122 		(n) & (1ULL << 27) ? 27 :	\
123 		(n) & (1ULL << 26) ? 26 :	\
124 		(n) & (1ULL << 25) ? 25 :	\
125 		(n) & (1ULL << 24) ? 24 :	\
126 		(n) & (1ULL << 23) ? 23 :	\
127 		(n) & (1ULL << 22) ? 22 :	\
128 		(n) & (1ULL << 21) ? 21 :	\
129 		(n) & (1ULL << 20) ? 20 :	\
130 		(n) & (1ULL << 19) ? 19 :	\
131 		(n) & (1ULL << 18) ? 18 :	\
132 		(n) & (1ULL << 17) ? 17 :	\
133 		(n) & (1ULL << 16) ? 16 :	\
134 		(n) & (1ULL << 15) ? 15 :	\
135 		(n) & (1ULL << 14) ? 14 :	\
136 		(n) & (1ULL << 13) ? 13 :	\
137 		(n) & (1ULL << 12) ? 12 :	\
138 		(n) & (1ULL << 11) ? 11 :	\
139 		(n) & (1ULL << 10) ? 10 :	\
140 		(n) & (1ULL <<  9) ?  9 :	\
141 		(n) & (1ULL <<  8) ?  8 :	\
142 		(n) & (1ULL <<  7) ?  7 :	\
143 		(n) & (1ULL <<  6) ?  6 :	\
144 		(n) & (1ULL <<  5) ?  5 :	\
145 		(n) & (1ULL <<  4) ?  4 :	\
146 		(n) & (1ULL <<  3) ?  3 :	\
147 		(n) & (1ULL <<  2) ?  2 :	\
148 		(n) & (1ULL <<  1) ?  1 :	\
149 		(n) & (1ULL <<  0) ?  0 :	\
150 		____ilog2_NaN()			\
151 				   ) :		\
152 	(sizeof(n) <= 4) ?			\
153 	__ilog2_u32(n) :			\
154 	__ilog2_u64(n)				\
155  )
156 
157 /**
158  * roundup_pow_of_two - round the given value up to nearest power of two
159  * @n - parameter
160  *
161  * round the given value up to the nearest power of two
162  * - the result is undefined when n == 0
163  * - this can be used to initialise global variables from constant data
164  */
165 #define roundup_pow_of_two(n)			\
166 (						\
167 	__builtin_constant_p(n) ? (		\
168 		(n == 1) ? 1 :			\
169 		(1UL << (ilog2((n) - 1) + 1))	\
170 				   ) :		\
171 	__roundup_pow_of_two(n)			\
172  )
173 
174 /**
175  * rounddown_pow_of_two - round the given value down to nearest power of two
176  * @n - parameter
177  *
178  * round the given value down to the nearest power of two
179  * - the result is undefined when n == 0
180  * - this can be used to initialise global variables from constant data
181  */
182 #define rounddown_pow_of_two(n)			\
183 (						\
184 	__builtin_constant_p(n) ? (		\
185 		(1UL << ilog2(n))) :		\
186 	__rounddown_pow_of_two(n)		\
187  )
188 
189 /**
190  * order_base_2 - calculate the (rounded up) base 2 order of the argument
191  * @n: parameter
192  *
193  * The first few values calculated by this routine:
194  *  ob2(0) = 0
195  *  ob2(1) = 0
196  *  ob2(2) = 1
197  *  ob2(3) = 2
198  *  ob2(4) = 2
199  *  ob2(5) = 3
200  *  ... and so on.
201  */
202 
203 #define order_base_2(n) ilog2(roundup_pow_of_two(n))
204 
205 #endif /* _LINUX_LOG2_H */
206