1 /* SPDX-License-Identifier: GPL-2.0+ */ 2 /* Integer base 2 logarithm calculation 3 * 4 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. 5 * Written by David Howells (dhowells (at) redhat.com) 6 * 7 * This program is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU General Public License 9 * as published by the Free Software Foundation; either version 10 * 2 of the License, or (at your option) any later version. 11 */ 12 13 #ifndef _LINUX_LOG2_H 14 #define _LINUX_LOG2_H 15 16 #include <linux/types.h> 17 #include <linux/bitops.h> 18 19 /* 20 * non-constant log of base 2 calculators 21 * - the arch may override these in asm/bitops.h if they can be implemented 22 * more efficiently than using fls() and fls64() 23 * - the arch is not required to handle n==0 if implementing the fallback 24 */ 25 #ifndef CONFIG_ARCH_HAS_ILOG2_U32 26 static inline __attribute__((const)) 27 int __ilog2_u32(u32 n) 28 { 29 return fls(n) - 1; 30 } 31 #endif 32 33 #ifndef CONFIG_ARCH_HAS_ILOG2_U64 34 static inline __attribute__((const)) 35 int __ilog2_u64(u64 n) 36 { 37 return fls64(n) - 1; 38 } 39 #endif 40 41 /** 42 * is_power_of_2() - check if a value is a power of two 43 * @n: the value to check 44 * 45 * Determine whether some value is a power of two, where zero is 46 * *not* considered a power of two. 47 * Return: true if @n is a power of 2, otherwise false. 48 */ 49 static inline __attribute__((const)) 50 bool is_power_of_2(unsigned long n) 51 { 52 return (n != 0 && ((n & (n - 1)) == 0)); 53 } 54 55 /** 56 * __roundup_pow_of_two() - round up to nearest power of two 57 * @n: value to round up 58 */ 59 static inline __attribute__((const)) 60 unsigned long __roundup_pow_of_two(unsigned long n) 61 { 62 return 1UL << fls_long(n - 1); 63 } 64 65 /** 66 * __rounddown_pow_of_two() - round down to nearest power of two 67 * @n: value to round down 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 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) < 2 ? 0 : \ 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 1) : \ 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 static inline __attribute_const__ 190 int __order_base_2(unsigned long n) 191 { 192 return n > 1 ? ilog2(n - 1) + 1 : 0; 193 } 194 195 /** 196 * order_base_2 - calculate the (rounded up) base 2 order of the argument 197 * @n: parameter 198 * 199 * The first few values calculated by this routine: 200 * ob2(0) = 0 201 * ob2(1) = 0 202 * ob2(2) = 1 203 * ob2(3) = 2 204 * ob2(4) = 2 205 * ob2(5) = 3 206 * ... and so on. 207 */ 208 #define order_base_2(n) \ 209 ( \ 210 __builtin_constant_p(n) ? ( \ 211 ((n) == 0 || (n) == 1) ? 0 : \ 212 ilog2((n) - 1) + 1) : \ 213 __order_base_2(n) \ 214 ) 215 #endif /* _LINUX_LOG2_H */ 216
