David Howells | f0d1b0b | 2006-12-08 02:37:49 -0800 | [diff] [blame] | 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 | |
David Howells | 312a0c1 | 2006-12-08 02:37:51 -0800 | [diff] [blame] | 46 | /* |
Robert P. J. Day | 63c2f78 | 2007-01-30 06:06:00 -0500 | [diff] [blame] | 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 | /* |
David Howells | 312a0c1 | 2006-12-08 02:37:51 -0800 | [diff] [blame] | 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 | |
David Howells | f0d1b0b | 2006-12-08 02:37:49 -0800 | [diff] [blame] | 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 | |
David Howells | 312a0c1 | 2006-12-08 02:37:51 -0800 | [diff] [blame] | 151 | /** |
| 152 | * roundup_pow_of_two - round the given value up to nearest power of two |
| 153 | * @n - parameter |
| 154 | * |
| 155 | * round the given balue 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 | |
David Howells | f0d1b0b | 2006-12-08 02:37:49 -0800 | [diff] [blame] | 168 | #endif /* _LINUX_LOG2_H */ |