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 * non-constant log of base 2 calculators 20 * - the arch may override these in asm/bitops.h if they can be implemented 21 * more efficiently than using fls() and fls64() 22 * - the arch is not required to handle n==0 if implementing the fallback 23 */ 24 #ifndef CONFIG_ARCH_HAS_ILOG2_U32 25 static inline __attribute__((const)) 26 int __ilog2_u32(u32 n) 27 { 28 return fls(n) - 1; 29 } 30 #endif 31 32 #ifndef CONFIG_ARCH_HAS_ILOG2_U64 33 static inline __attribute__((const)) 34 int __ilog2_u64(u64 n) 35 { 36 return fls64(n) - 1; 37 } 38 #endif 39 40 /** 41 * is_power_of_2() - check if a value is a power of two 42 * @n: the value to check 43 * 44 * Determine whether some value is a power of two, where zero is 45 * *not* considered a power of two. 46 * Return: true if @n is a power of 2, otherwise false. 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 * __roundup_pow_of_two() - round up to nearest power of two 56 * @n: value to round up 57 */ 58 static inline __attribute__((const)) 59 unsigned long __roundup_pow_of_two(unsigned long n) 60 { 61 return 1UL << fls_long(n - 1); 62 } 63 64 /** 65 * __rounddown_pow_of_two() - round down to nearest power of two 66 * @n: value to round down 67 */ 68 static inline __attribute__((const)) 69 unsigned long __rounddown_pow_of_two(unsigned long n) 70 { 71 return 1UL << (fls_long(n) - 1); 72 } 73 74 /** 75 * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value 76 * @n: parameter 77 * 78 * Use this where sparse expects a true constant expression, e.g. for array 79 * indices. 80 */ 81 #define const_ilog2(n) \ 82 ( \ 83 __builtin_constant_p(n) ? ( \ 84 (n) < 2 ? 0 : \ 85 (n) & (1ULL << 63) ? 63 : \ 86 (n) & (1ULL << 62) ? 62 : \ 87 (n) & (1ULL << 61) ? 61 : \ 88 (n) & (1ULL << 60) ? 60 : \ 89 (n) & (1ULL << 59) ? 59 : \ 90 (n) & (1ULL << 58) ? 58 : \ 91 (n) & (1ULL << 57) ? 57 : \ 92 (n) & (1ULL << 56) ? 56 : \ 93 (n) & (1ULL << 55) ? 55 : \ 94 (n) & (1ULL << 54) ? 54 : \ 95 (n) & (1ULL << 53) ? 53 : \ 96 (n) & (1ULL << 52) ? 52 : \ 97 (n) & (1ULL << 51) ? 51 : \ 98 (n) & (1ULL << 50) ? 50 : \ 99 (n) & (1ULL << 49) ? 49 : \ 100 (n) & (1ULL << 48) ? 48 : \ 101 (n) & (1ULL << 47) ? 47 : \ 102 (n) & (1ULL << 46) ? 46 : \ 103 (n) & (1ULL << 45) ? 45 : \ 104 (n) & (1ULL << 44) ? 44 : \ 105 (n) & (1ULL << 43) ? 43 : \ 106 (n) & (1ULL << 42) ? 42 : \ 107 (n) & (1ULL << 41) ? 41 : \ 108 (n) & (1ULL << 40) ? 40 : \ 109 (n) & (1ULL << 39) ? 39 : \ 110 (n) & (1ULL << 38) ? 38 : \ 111 (n) & (1ULL << 37) ? 37 : \ 112 (n) & (1ULL << 36) ? 36 : \ 113 (n) & (1ULL << 35) ? 35 : \ 114 (n) & (1ULL << 34) ? 34 : \ 115 (n) & (1ULL << 33) ? 33 : \ 116 (n) & (1ULL << 32) ? 32 : \ 117 (n) & (1ULL << 31) ? 31 : \ 118 (n) & (1ULL << 30) ? 30 : \ 119 (n) & (1ULL << 29) ? 29 : \ 120 (n) & (1ULL << 28) ? 28 : \ 121 (n) & (1ULL << 27) ? 27 : \ 122 (n) & (1ULL << 26) ? 26 : \ 123 (n) & (1ULL << 25) ? 25 : \ 124 (n) & (1ULL << 24) ? 24 : \ 125 (n) & (1ULL << 23) ? 23 : \ 126 (n) & (1ULL << 22) ? 22 : \ 127 (n) & (1ULL << 21) ? 21 : \ 128 (n) & (1ULL << 20) ? 20 : \ 129 (n) & (1ULL << 19) ? 19 : \ 130 (n) & (1ULL << 18) ? 18 : \ 131 (n) & (1ULL << 17) ? 17 : \ 132 (n) & (1ULL << 16) ? 16 : \ 133 (n) & (1ULL << 15) ? 15 : \ 134 (n) & (1ULL << 14) ? 14 : \ 135 (n) & (1ULL << 13) ? 13 : \ 136 (n) & (1ULL << 12) ? 12 : \ 137 (n) & (1ULL << 11) ? 11 : \ 138 (n) & (1ULL << 10) ? 10 : \ 139 (n) & (1ULL << 9) ? 9 : \ 140 (n) & (1ULL << 8) ? 8 : \ 141 (n) & (1ULL << 7) ? 7 : \ 142 (n) & (1ULL << 6) ? 6 : \ 143 (n) & (1ULL << 5) ? 5 : \ 144 (n) & (1ULL << 4) ? 4 : \ 145 (n) & (1ULL << 3) ? 3 : \ 146 (n) & (1ULL << 2) ? 2 : \ 147 1) : \ 148 -1) 149 150 /** 151 * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value 152 * @n: parameter 153 * 154 * constant-capable log of base 2 calculation 155 * - this can be used to initialise global variables from constant data, hence 156 * the massive ternary operator construction 157 * 158 * selects the appropriately-sized optimised version depending on sizeof(n) 159 */ 160 #define ilog2(n) \ 161 ( \ 162 __builtin_constant_p(n) ? \ 163 const_ilog2(n) : \ 164 (sizeof(n) <= 4) ? \ 165 __ilog2_u32(n) : \ 166 __ilog2_u64(n) \ 167 ) 168 169 /** 170 * roundup_pow_of_two - round the given value up to nearest power of two 171 * @n: parameter 172 * 173 * round the given value up to the nearest power of two 174 * - the result is undefined when n == 0 175 * - this can be used to initialise global variables from constant data 176 */ 177 #define roundup_pow_of_two(n) \ 178 ( \ 179 __builtin_constant_p(n) ? ( \ 180 (n == 1) ? 1 : \ 181 (1UL << (ilog2((n) - 1) + 1)) \ 182 ) : \ 183 __roundup_pow_of_two(n) \ 184 ) 185 186 /** 187 * rounddown_pow_of_two - round the given value down to nearest power of two 188 * @n: parameter 189 * 190 * round the given value down to the nearest power of two 191 * - the result is undefined when n == 0 192 * - this can be used to initialise global variables from constant data 193 */ 194 #define rounddown_pow_of_two(n) \ 195 ( \ 196 __builtin_constant_p(n) ? ( \ 197 (1UL << ilog2(n))) : \ 198 __rounddown_pow_of_two(n) \ 199 ) 200 201 static inline __attribute_const__ 202 int __order_base_2(unsigned long n) 203 { 204 return n > 1 ? ilog2(n - 1) + 1 : 0; 205 } 206 207 /** 208 * order_base_2 - calculate the (rounded up) base 2 order of the argument 209 * @n: parameter 210 * 211 * The first few values calculated by this routine: 212 * ob2(0) = 0 213 * ob2(1) = 0 214 * ob2(2) = 1 215 * ob2(3) = 2 216 * ob2(4) = 2 217 * ob2(5) = 3 218 * ... and so on. 219 */ 220 #define order_base_2(n) \ 221 ( \ 222 __builtin_constant_p(n) ? ( \ 223 ((n) == 0 || (n) == 1) ? 0 : \ 224 ilog2((n) - 1) + 1) : \ 225 __order_base_2(n) \ 226 ) 227 #endif /* _LINUX_LOG2_H */ 228