1 /* SPDX-License-Identifier: GPL-2.0-or-later */ 2 /* Integer base 2 logarithm calculation 3 * 4 * Copyright (C) 2006 Red Hat, Inc. All Rights Reserved. 5 * Written by David Howells (dhowells@redhat.com) 6 */ 7 8 #ifndef _LINUX_LOG2_H 9 #define _LINUX_LOG2_H 10 11 #include <linux/types.h> 12 #include <linux/bitops.h> 13 14 /* 15 * non-constant log of base 2 calculators 16 * - the arch may override these in asm/bitops.h if they can be implemented 17 * more efficiently than using fls() and fls64() 18 * - the arch is not required to handle n==0 if implementing the fallback 19 */ 20 #ifndef CONFIG_ARCH_HAS_ILOG2_U32 21 static __always_inline __attribute__((const)) __ilog2_u32(u32 n)22int __ilog2_u32(u32 n) 23 { 24 return fls(n) - 1; 25 } 26 #endif 27 28 #ifndef CONFIG_ARCH_HAS_ILOG2_U64 29 static __always_inline __attribute__((const)) __ilog2_u64(u64 n)30int __ilog2_u64(u64 n) 31 { 32 return fls64(n) - 1; 33 } 34 #endif 35 36 /** 37 * is_power_of_2() - check if a value is a power of two 38 * @n: the value to check 39 * 40 * Determine whether some value is a power of two, where zero is 41 * *not* considered a power of two. 42 * Return: true if @n is a power of 2, otherwise false. 43 */ 44 static inline __attribute__((const)) is_power_of_2(unsigned long n)45bool is_power_of_2(unsigned long n) 46 { 47 return (n != 0 && ((n & (n - 1)) == 0)); 48 } 49 50 /** 51 * __roundup_pow_of_two() - round up to nearest power of two 52 * @n: value to round up 53 */ 54 static inline __attribute__((const)) __roundup_pow_of_two(unsigned long n)55unsigned long __roundup_pow_of_two(unsigned long n) 56 { 57 return 1UL << fls_long(n - 1); 58 } 59 60 /** 61 * __rounddown_pow_of_two() - round down to nearest power of two 62 * @n: value to round down 63 */ 64 static inline __attribute__((const)) __rounddown_pow_of_two(unsigned long n)65unsigned long __rounddown_pow_of_two(unsigned long n) 66 { 67 return 1UL << (fls_long(n) - 1); 68 } 69 70 /** 71 * const_ilog2 - log base 2 of 32-bit or a 64-bit constant unsigned value 72 * @n: parameter 73 * 74 * Use this where sparse expects a true constant expression, e.g. for array 75 * indices. 76 */ 77 #define const_ilog2(n) \ 78 ( \ 79 __builtin_constant_p(n) ? ( \ 80 (n) < 2 ? 0 : \ 81 (n) & (1ULL << 63) ? 63 : \ 82 (n) & (1ULL << 62) ? 62 : \ 83 (n) & (1ULL << 61) ? 61 : \ 84 (n) & (1ULL << 60) ? 60 : \ 85 (n) & (1ULL << 59) ? 59 : \ 86 (n) & (1ULL << 58) ? 58 : \ 87 (n) & (1ULL << 57) ? 57 : \ 88 (n) & (1ULL << 56) ? 56 : \ 89 (n) & (1ULL << 55) ? 55 : \ 90 (n) & (1ULL << 54) ? 54 : \ 91 (n) & (1ULL << 53) ? 53 : \ 92 (n) & (1ULL << 52) ? 52 : \ 93 (n) & (1ULL << 51) ? 51 : \ 94 (n) & (1ULL << 50) ? 50 : \ 95 (n) & (1ULL << 49) ? 49 : \ 96 (n) & (1ULL << 48) ? 48 : \ 97 (n) & (1ULL << 47) ? 47 : \ 98 (n) & (1ULL << 46) ? 46 : \ 99 (n) & (1ULL << 45) ? 45 : \ 100 (n) & (1ULL << 44) ? 44 : \ 101 (n) & (1ULL << 43) ? 43 : \ 102 (n) & (1ULL << 42) ? 42 : \ 103 (n) & (1ULL << 41) ? 41 : \ 104 (n) & (1ULL << 40) ? 40 : \ 105 (n) & (1ULL << 39) ? 39 : \ 106 (n) & (1ULL << 38) ? 38 : \ 107 (n) & (1ULL << 37) ? 37 : \ 108 (n) & (1ULL << 36) ? 36 : \ 109 (n) & (1ULL << 35) ? 35 : \ 110 (n) & (1ULL << 34) ? 34 : \ 111 (n) & (1ULL << 33) ? 33 : \ 112 (n) & (1ULL << 32) ? 32 : \ 113 (n) & (1ULL << 31) ? 31 : \ 114 (n) & (1ULL << 30) ? 30 : \ 115 (n) & (1ULL << 29) ? 29 : \ 116 (n) & (1ULL << 28) ? 28 : \ 117 (n) & (1ULL << 27) ? 27 : \ 118 (n) & (1ULL << 26) ? 26 : \ 119 (n) & (1ULL << 25) ? 25 : \ 120 (n) & (1ULL << 24) ? 24 : \ 121 (n) & (1ULL << 23) ? 23 : \ 122 (n) & (1ULL << 22) ? 22 : \ 123 (n) & (1ULL << 21) ? 21 : \ 124 (n) & (1ULL << 20) ? 20 : \ 125 (n) & (1ULL << 19) ? 19 : \ 126 (n) & (1ULL << 18) ? 18 : \ 127 (n) & (1ULL << 17) ? 17 : \ 128 (n) & (1ULL << 16) ? 16 : \ 129 (n) & (1ULL << 15) ? 15 : \ 130 (n) & (1ULL << 14) ? 14 : \ 131 (n) & (1ULL << 13) ? 13 : \ 132 (n) & (1ULL << 12) ? 12 : \ 133 (n) & (1ULL << 11) ? 11 : \ 134 (n) & (1ULL << 10) ? 10 : \ 135 (n) & (1ULL << 9) ? 9 : \ 136 (n) & (1ULL << 8) ? 8 : \ 137 (n) & (1ULL << 7) ? 7 : \ 138 (n) & (1ULL << 6) ? 6 : \ 139 (n) & (1ULL << 5) ? 5 : \ 140 (n) & (1ULL << 4) ? 4 : \ 141 (n) & (1ULL << 3) ? 3 : \ 142 (n) & (1ULL << 2) ? 2 : \ 143 1) : \ 144 -1) 145 146 /** 147 * ilog2 - log base 2 of 32-bit or a 64-bit unsigned value 148 * @n: parameter 149 * 150 * constant-capable log of base 2 calculation 151 * - this can be used to initialise global variables from constant data, hence 152 * the massive ternary operator construction 153 * 154 * selects the appropriately-sized optimised version depending on sizeof(n) 155 */ 156 #define ilog2(n) \ 157 ( \ 158 __builtin_constant_p(n) ? \ 159 ((n) < 2 ? 0 : \ 160 63 - __builtin_clzll(n)) : \ 161 (sizeof(n) <= 4) ? \ 162 __ilog2_u32(n) : \ 163 __ilog2_u64(n) \ 164 ) 165 166 /** 167 * roundup_pow_of_two - round the given value up to nearest power of two 168 * @n: parameter 169 * 170 * round the given value up to the nearest power of two 171 * - the result is undefined when n == 0 172 * - this can be used to initialise global variables from constant data 173 */ 174 #define roundup_pow_of_two(n) \ 175 ( \ 176 __builtin_constant_p(n) ? ( \ 177 ((n) == 1) ? 1 : \ 178 (1UL << (ilog2((n) - 1) + 1)) \ 179 ) : \ 180 __roundup_pow_of_two(n) \ 181 ) 182 183 /** 184 * rounddown_pow_of_two - round the given value down to nearest power of two 185 * @n: parameter 186 * 187 * round the given value down to the nearest power of two 188 * - the result is undefined when n == 0 189 * - this can be used to initialise global variables from constant data 190 */ 191 #define rounddown_pow_of_two(n) \ 192 ( \ 193 __builtin_constant_p(n) ? ( \ 194 (1UL << ilog2(n))) : \ 195 __rounddown_pow_of_two(n) \ 196 ) 197 198 static inline __attribute_const__ __order_base_2(unsigned long n)199int __order_base_2(unsigned long n) 200 { 201 return n > 1 ? ilog2(n - 1) + 1 : 0; 202 } 203 204 /** 205 * order_base_2 - calculate the (rounded up) base 2 order of the argument 206 * @n: parameter 207 * 208 * The first few values calculated by this routine: 209 * ob2(0) = 0 210 * ob2(1) = 0 211 * ob2(2) = 1 212 * ob2(3) = 2 213 * ob2(4) = 2 214 * ob2(5) = 3 215 * ... and so on. 216 */ 217 #define order_base_2(n) \ 218 ( \ 219 __builtin_constant_p(n) ? ( \ 220 ((n) == 0 || (n) == 1) ? 0 : \ 221 ilog2((n) - 1) + 1) : \ 222 __order_base_2(n) \ 223 ) 224 225 static inline __attribute__((const)) __bits_per(unsigned long n)226int __bits_per(unsigned long n) 227 { 228 if (n < 2) 229 return 1; 230 if (is_power_of_2(n)) 231 return order_base_2(n) + 1; 232 return order_base_2(n); 233 } 234 235 /** 236 * bits_per - calculate the number of bits required for the argument 237 * @n: parameter 238 * 239 * This is constant-capable and can be used for compile time 240 * initializations, e.g bitfields. 241 * 242 * The first few values calculated by this routine: 243 * bf(0) = 1 244 * bf(1) = 1 245 * bf(2) = 2 246 * bf(3) = 2 247 * bf(4) = 3 248 * ... and so on. 249 */ 250 #define bits_per(n) \ 251 ( \ 252 __builtin_constant_p(n) ? ( \ 253 ((n) == 0 || (n) == 1) \ 254 ? 1 : ilog2(n) + 1 \ 255 ) : \ 256 __bits_per(n) \ 257 ) 258 #endif /* _LINUX_LOG2_H */ 259