| 1 | |
| 2 | *
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| 3 | * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
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| 4 | * Written by David Howells ([email protected])
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| 5 | *
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| 6 | * This program is free software; you can redistribute it and/or
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| 7 | * modify it under the terms of the GNU General Public License
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| 8 | * as published by the Free Software Foundation; either version
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| 9 | * 2 of the License, or (at your option) any later version.
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| 10 |
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| 11 |
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| 12 | #ifndef _LINUX_LOG2_H
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| 13 | #define _LINUX_LOG2_H
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| 14 |
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| 15 | #include <linux/types.h>
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| 16 | #include <linux/bitops.h>
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| 17 |
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| 18 | |
| 19 | * non-constant log of base 2 calculators
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| 20 | * - the arch may override these in asm/bitops.h if they can be implemented
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| 21 | * more efficiently than using fls() and fls64()
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| 22 | * - the arch is not required to handle n==0 if implementing the fallback
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| 23 |
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| 24 | #ifndef CONFIG_ARCH_HAS_ILOG2_U32
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| 25 | static inline __attribute__((const))
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| 26 | int __ilog2_u32(u32 n)
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| 27 | {
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| 28 | return fls(n) - 1;
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| 29 | }
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| 30 | #endif
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| 31 |
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| 32 | #ifndef CONFIG_ARCH_HAS_ILOG2_U64
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| 33 | static inline __attribute__((const))
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| 34 | int __ilog2_u64(u64 n)
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| 35 | {
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| 36 | return fls64(n) - 1;
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| 37 | }
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| 38 | #endif
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| 39 |
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| 40 | |
| 41 | * Determine whether some value is a power of two, where zero is
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| 42 | * *not* considered a power of two.
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| 43 |
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| 44 |
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| 45 | static inline __attribute__((const))
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| 46 | bool is_power_of_2(unsigned long n)
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| 47 | {
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| 48 | return (n != 0 && ((n & (n - 1)) == 0));
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| 49 | }
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| 50 |
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| 51 | |
| 52 | * round up to nearest power of two
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| 53 |
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| 54 | static inline __attribute__((const))
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| 55 | unsigned long __roundup_pow_of_two(unsigned long n)
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| 56 | {
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| 57 | return 1UL << fls_long(n - 1);
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| 58 | }
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| 59 |
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| 60 | |
| 61 | * round down to nearest power of two
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| 62 |
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| 63 | static inline __attribute__((const))
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| 64 | unsigned long __rounddown_pow_of_two(unsigned long n)
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| 65 | {
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| 66 | return 1UL << (fls_long(n) - 1);
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| 67 | }
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| 68 |
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| 69 | |
| 70 | * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
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| 71 | * @n - parameter
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| 72 | *
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| 73 | * constant-capable log of base 2 calculation
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| 74 | * - this can be used to initialise global variables from constant data, hence
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| 75 | * the massive ternary operator construction
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| 76 | *
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| 77 | * selects the appropriately-sized optimised version depending on sizeof(n)
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| 78 |
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| 79 | #define ilog2(n) \
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| 80 | ( \
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| 81 | __builtin_constant_p(n) ? ( \
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| 82 | (n) < 2 ? 0 : \
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| 83 | (n) & (1ULL << 63) ? 63 : \
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| 84 | (n) & (1ULL << 62) ? 62 : \
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| 85 | (n) & (1ULL << 61) ? 61 : \
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| 86 | (n) & (1ULL << 60) ? 60 : \
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| 87 | (n) & (1ULL << 59) ? 59 : \
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| 88 | (n) & (1ULL << 58) ? 58 : \
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| 89 | (n) & (1ULL << 57) ? 57 : \
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| 90 | (n) & (1ULL << 56) ? 56 : \
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| 91 | (n) & (1ULL << 55) ? 55 : \
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| 92 | (n) & (1ULL << 54) ? 54 : \
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| 93 | (n) & (1ULL << 53) ? 53 : \
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| 94 | (n) & (1ULL << 52) ? 52 : \
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| 95 | (n) & (1ULL << 51) ? 51 : \
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| 96 | (n) & (1ULL << 50) ? 50 : \
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| 97 | (n) & (1ULL << 49) ? 49 : \
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| 98 | (n) & (1ULL << 48) ? 48 : \
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| 99 | (n) & (1ULL << 47) ? 47 : \
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| 100 | (n) & (1ULL << 46) ? 46 : \
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| 101 | (n) & (1ULL << 45) ? 45 : \
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| 102 | (n) & (1ULL << 44) ? 44 : \
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| 103 | (n) & (1ULL << 43) ? 43 : \
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| 104 | (n) & (1ULL << 42) ? 42 : \
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| 105 | (n) & (1ULL << 41) ? 41 : \
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| 106 | (n) & (1ULL << 40) ? 40 : \
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| 107 | (n) & (1ULL << 39) ? 39 : \
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| 108 | (n) & (1ULL << 38) ? 38 : \
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| 109 | (n) & (1ULL << 37) ? 37 : \
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| 110 | (n) & (1ULL << 36) ? 36 : \
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| 111 | (n) & (1ULL << 35) ? 35 : \
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| 112 | (n) & (1ULL << 34) ? 34 : \
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| 113 | (n) & (1ULL << 33) ? 33 : \
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| 114 | (n) & (1ULL << 32) ? 32 : \
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| 115 | (n) & (1ULL << 31) ? 31 : \
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| 116 | (n) & (1ULL << 30) ? 30 : \
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| 117 | (n) & (1ULL << 29) ? 29 : \
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| 118 | (n) & (1ULL << 28) ? 28 : \
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| 119 | (n) & (1ULL << 27) ? 27 : \
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| 120 | (n) & (1ULL << 26) ? 26 : \
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| 121 | (n) & (1ULL << 25) ? 25 : \
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| 122 | (n) & (1ULL << 24) ? 24 : \
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| 123 | (n) & (1ULL << 23) ? 23 : \
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| 124 | (n) & (1ULL << 22) ? 22 : \
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| 125 | (n) & (1ULL << 21) ? 21 : \
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| 126 | (n) & (1ULL << 20) ? 20 : \
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| 127 | (n) & (1ULL << 19) ? 19 : \
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| 128 | (n) & (1ULL << 18) ? 18 : \
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| 129 | (n) & (1ULL << 17) ? 17 : \
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| 130 | (n) & (1ULL << 16) ? 16 : \
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| 131 | (n) & (1ULL << 15) ? 15 : \
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| 132 | (n) & (1ULL << 14) ? 14 : \
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| 133 | (n) & (1ULL << 13) ? 13 : \
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| 134 | (n) & (1ULL << 12) ? 12 : \
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| 135 | (n) & (1ULL << 11) ? 11 : \
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| 136 | (n) & (1ULL << 10) ? 10 : \
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| 137 | (n) & (1ULL << 9) ? 9 : \
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| 138 | (n) & (1ULL << 8) ? 8 : \
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| 139 | (n) & (1ULL << 7) ? 7 : \
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| 140 | (n) & (1ULL << 6) ? 6 : \
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| 141 | (n) & (1ULL << 5) ? 5 : \
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| 142 | (n) & (1ULL << 4) ? 4 : \
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| 143 | (n) & (1ULL << 3) ? 3 : \
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| 144 | (n) & (1ULL << 2) ? 2 : \
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| 145 | 1 ) : \
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| 146 | (sizeof(n) <= 4) ? \
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| 147 | __ilog2_u32(n) : \
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| 148 | __ilog2_u64(n) \
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| 149 | )
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| 150 |
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| 151 | |
| 152 | * roundup_pow_of_two - round the given value up to nearest power of two
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| 153 | * @n - parameter
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| 154 | *
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| 155 | * round the given value up to the nearest power of two
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| 156 | * - the result is undefined when n == 0
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| 157 | * - this can be used to initialise global variables from constant data
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| 158 |
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| 159 | #define roundup_pow_of_two(n) \
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| 160 | ( \
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| 161 | __builtin_constant_p(n) ? ( \
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| 162 | (n == 1) ? 1 : \
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| 163 | (1UL << (ilog2((n) - 1) + 1)) \
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| 164 | ) : \
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| 165 | __roundup_pow_of_two(n) \
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| 166 | )
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| 167 |
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| 168 | |
| 169 | * rounddown_pow_of_two - round the given value down to nearest power of two
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| 170 | * @n - parameter
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| 171 | *
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| 172 | * round the given value down to the nearest power of two
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| 173 | * - the result is undefined when n == 0
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| 174 | * - this can be used to initialise global variables from constant data
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| 175 |
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| 176 | #define rounddown_pow_of_two(n) \
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| 177 | ( \
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| 178 | __builtin_constant_p(n) ? ( \
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| 179 | (1UL << ilog2(n))) : \
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| 180 | __rounddown_pow_of_two(n) \
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| 181 | )
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| 182 |
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| 183 | |
| 184 | * order_base_2 - calculate the (rounded up) base 2 order of the argument
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| 185 | * @n: parameter
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| 186 | *
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| 187 | * The first few values calculated by this routine:
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| 188 | * ob2(0) = 0
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| 189 | * ob2(1) = 0
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| 190 | * ob2(2) = 1
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| 191 | * ob2(3) = 2
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| 192 | * ob2(4) = 2
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| 193 | * ob2(5) = 3
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| 194 | * ... and so on.
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| 195 |
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| 196 |
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| 197 | static inline __attribute_const__
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| 198 | int __order_base_2(unsigned long n)
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| 199 | {
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| 200 | return n > 1 ? ilog2(n - 1) + 1 : 0;
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| 201 | }
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| 202 |
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| 203 | #define order_base_2(n) \
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| 204 | ( \
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| 205 | __builtin_constant_p(n) ? ( \
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| 206 | ((n) == 0 || (n) == 1) ? 0 : \
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| 207 | ilog2((n) - 1) + 1) : \
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| 208 | __order_base_2(n) \
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| 209 | )
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| 210 | #endif
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