Root/
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 | * round down to nearest power of two |
68 | */ |
69 | static inline __attribute__((const)) |
70 | unsigned long __rounddown_pow_of_two(unsigned long n) |
71 | { |
72 | return 1UL << (fls_long(n) - 1); |
73 | } |
74 | |
75 | /** |
76 | * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value |
77 | * @n - parameter |
78 | * |
79 | * constant-capable log of base 2 calculation |
80 | * - this can be used to initialise global variables from constant data, hence |
81 | * the massive ternary operator construction |
82 | * |
83 | * selects the appropriately-sized optimised version depending on sizeof(n) |
84 | */ |
85 | #define ilog2(n) \ |
86 | ( \ |
87 | __builtin_constant_p(n) ? ( \ |
88 | (n) < 1 ? ____ilog2_NaN() : \ |
89 | (n) & (1ULL << 63) ? 63 : \ |
90 | (n) & (1ULL << 62) ? 62 : \ |
91 | (n) & (1ULL << 61) ? 61 : \ |
92 | (n) & (1ULL << 60) ? 60 : \ |
93 | (n) & (1ULL << 59) ? 59 : \ |
94 | (n) & (1ULL << 58) ? 58 : \ |
95 | (n) & (1ULL << 57) ? 57 : \ |
96 | (n) & (1ULL << 56) ? 56 : \ |
97 | (n) & (1ULL << 55) ? 55 : \ |
98 | (n) & (1ULL << 54) ? 54 : \ |
99 | (n) & (1ULL << 53) ? 53 : \ |
100 | (n) & (1ULL << 52) ? 52 : \ |
101 | (n) & (1ULL << 51) ? 51 : \ |
102 | (n) & (1ULL << 50) ? 50 : \ |
103 | (n) & (1ULL << 49) ? 49 : \ |
104 | (n) & (1ULL << 48) ? 48 : \ |
105 | (n) & (1ULL << 47) ? 47 : \ |
106 | (n) & (1ULL << 46) ? 46 : \ |
107 | (n) & (1ULL << 45) ? 45 : \ |
108 | (n) & (1ULL << 44) ? 44 : \ |
109 | (n) & (1ULL << 43) ? 43 : \ |
110 | (n) & (1ULL << 42) ? 42 : \ |
111 | (n) & (1ULL << 41) ? 41 : \ |
112 | (n) & (1ULL << 40) ? 40 : \ |
113 | (n) & (1ULL << 39) ? 39 : \ |
114 | (n) & (1ULL << 38) ? 38 : \ |
115 | (n) & (1ULL << 37) ? 37 : \ |
116 | (n) & (1ULL << 36) ? 36 : \ |
117 | (n) & (1ULL << 35) ? 35 : \ |
118 | (n) & (1ULL << 34) ? 34 : \ |
119 | (n) & (1ULL << 33) ? 33 : \ |
120 | (n) & (1ULL << 32) ? 32 : \ |
121 | (n) & (1ULL << 31) ? 31 : \ |
122 | (n) & (1ULL << 30) ? 30 : \ |
123 | (n) & (1ULL << 29) ? 29 : \ |
124 | (n) & (1ULL << 28) ? 28 : \ |
125 | (n) & (1ULL << 27) ? 27 : \ |
126 | (n) & (1ULL << 26) ? 26 : \ |
127 | (n) & (1ULL << 25) ? 25 : \ |
128 | (n) & (1ULL << 24) ? 24 : \ |
129 | (n) & (1ULL << 23) ? 23 : \ |
130 | (n) & (1ULL << 22) ? 22 : \ |
131 | (n) & (1ULL << 21) ? 21 : \ |
132 | (n) & (1ULL << 20) ? 20 : \ |
133 | (n) & (1ULL << 19) ? 19 : \ |
134 | (n) & (1ULL << 18) ? 18 : \ |
135 | (n) & (1ULL << 17) ? 17 : \ |
136 | (n) & (1ULL << 16) ? 16 : \ |
137 | (n) & (1ULL << 15) ? 15 : \ |
138 | (n) & (1ULL << 14) ? 14 : \ |
139 | (n) & (1ULL << 13) ? 13 : \ |
140 | (n) & (1ULL << 12) ? 12 : \ |
141 | (n) & (1ULL << 11) ? 11 : \ |
142 | (n) & (1ULL << 10) ? 10 : \ |
143 | (n) & (1ULL << 9) ? 9 : \ |
144 | (n) & (1ULL << 8) ? 8 : \ |
145 | (n) & (1ULL << 7) ? 7 : \ |
146 | (n) & (1ULL << 6) ? 6 : \ |
147 | (n) & (1ULL << 5) ? 5 : \ |
148 | (n) & (1ULL << 4) ? 4 : \ |
149 | (n) & (1ULL << 3) ? 3 : \ |
150 | (n) & (1ULL << 2) ? 2 : \ |
151 | (n) & (1ULL << 1) ? 1 : \ |
152 | (n) & (1ULL << 0) ? 0 : \ |
153 | ____ilog2_NaN() \ |
154 | ) : \ |
155 | (sizeof(n) <= 4) ? \ |
156 | __ilog2_u32(n) : \ |
157 | __ilog2_u64(n) \ |
158 | ) |
159 | |
160 | /** |
161 | * roundup_pow_of_two - round the given value up to nearest power of two |
162 | * @n - parameter |
163 | * |
164 | * round the given value up to the nearest power of two |
165 | * - the result is undefined when n == 0 |
166 | * - this can be used to initialise global variables from constant data |
167 | */ |
168 | #define roundup_pow_of_two(n) \ |
169 | ( \ |
170 | __builtin_constant_p(n) ? ( \ |
171 | (n == 1) ? 1 : \ |
172 | (1UL << (ilog2((n) - 1) + 1)) \ |
173 | ) : \ |
174 | __roundup_pow_of_two(n) \ |
175 | ) |
176 | |
177 | /** |
178 | * rounddown_pow_of_two - round the given value down to nearest power of two |
179 | * @n - parameter |
180 | * |
181 | * round the given value down to the nearest power of two |
182 | * - the result is undefined when n == 0 |
183 | * - this can be used to initialise global variables from constant data |
184 | */ |
185 | #define rounddown_pow_of_two(n) \ |
186 | ( \ |
187 | __builtin_constant_p(n) ? ( \ |
188 | (1UL << ilog2(n))) : \ |
189 | __rounddown_pow_of_two(n) \ |
190 | ) |
191 | |
192 | /** |
193 | * order_base_2 - calculate the (rounded up) base 2 order of the argument |
194 | * @n: parameter |
195 | * |
196 | * The first few values calculated by this routine: |
197 | * ob2(0) = 0 |
198 | * ob2(1) = 0 |
199 | * ob2(2) = 1 |
200 | * ob2(3) = 2 |
201 | * ob2(4) = 2 |
202 | * ob2(5) = 3 |
203 | * ... and so on. |
204 | */ |
205 | |
206 | #define order_base_2(n) ilog2(roundup_pow_of_two(n)) |
207 | |
208 | #endif /* _LINUX_LOG2_H */ |
209 |
Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master
Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9