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@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 * deal with unrepresentable constant logarithms 16 */ 17 extern __attribute__((const, noreturn)) 18 int ____ilog2_NaN(void); 19 20 /* 21 * non-constant log of base 2 calculators 22 * - the arch may override these in asm/bitops.h if they can be implemented 23 * more efficiently than using fls() and fls64() 24 * - the arch is not required to handle n==0 if implementing the fallback 25 */ 26 #ifndef CONFIG_ARCH_HAS_ILOG2_U32 27 static inline __attribute__((const)) 28 int __ilog2_u32(u32 n) 29 { 30 return fls(n) - 1; 31 } 32 #endif 33 34 #ifndef CONFIG_ARCH_HAS_ILOG2_U64 35 static inline __attribute__((const)) 36 int __ilog2_u64(u64 n) 37 { 38 return fls64(n) - 1; 39 } 40 #endif 41 42 /* 43 * Determine whether some value is a power of two, where zero is 44 * *not* considered a power of two. 45 */ 46 47 static inline __attribute__((const)) 48 bool is_power_of_2(unsigned long n) 49 { 50 return (n != 0 && ((n & (n - 1)) == 0)); 51 } 52 53 /* 54 * round up to nearest power of two 55 */ 56 static inline __attribute__((const)) 57 unsigned long __roundup_pow_of_two(unsigned long n) 58 { 59 return 1UL << fls_long(n - 1); 60 } 61 62 /* 63 * round down to nearest power of two 64 */ 65 static inline __attribute__((const)) 66 unsigned long __rounddown_pow_of_two(unsigned long n) 67 { 68 return 1UL << (fls_long(n) - 1); 69 } 70 71 /** 72 * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value 73 * @n - parameter 74 * 75 * constant-capable log of base 2 calculation 76 * - this can be used to initialise global variables from constant data, hence 77 * the massive ternary operator construction 78 * 79 * selects the appropriately-sized optimised version depending on sizeof(n) 80 */ 81 #define ilog2(n) \ 82 ( \ 83 __builtin_constant_p(n) ? ( \ 84 (n) < 1 ? ____ilog2_NaN() : \ 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 (n) & (1ULL << 1) ? 1 : \ 148 (n) & (1ULL << 0) ? 0 : \ 149 ____ilog2_NaN() \ 150 ) : \ 151 (sizeof(n) <= 4) ? \ 152 __ilog2_u32(n) : \ 153 __ilog2_u64(n) \ 154 ) 155 156 /** 157 * roundup_pow_of_two - round the given value up to nearest power of two 158 * @n - parameter 159 * 160 * round the given value up to the nearest power of two 161 * - the result is undefined when n == 0 162 * - this can be used to initialise global variables from constant data 163 */ 164 #define roundup_pow_of_two(n) \ 165 ( \ 166 __builtin_constant_p(n) ? ( \ 167 (n == 1) ? 1 : \ 168 (1UL << (ilog2((n) - 1) + 1)) \ 169 ) : \ 170 __roundup_pow_of_two(n) \ 171 ) 172 173 /** 174 * rounddown_pow_of_two - round the given value down to nearest power of two 175 * @n - parameter 176 * 177 * round the given value down to the nearest power of two 178 * - the result is undefined when n == 0 179 * - this can be used to initialise global variables from constant data 180 */ 181 #define rounddown_pow_of_two(n) \ 182 ( \ 183 __builtin_constant_p(n) ? ( \ 184 (1UL << ilog2(n))) : \ 185 __rounddown_pow_of_two(n) \ 186 ) 187 188 /** 189 * order_base_2 - calculate the (rounded up) base 2 order of the argument 190 * @n: parameter 191 * 192 * The first few values calculated by this routine: 193 * ob2(0) = 0 194 * ob2(1) = 0 195 * ob2(2) = 1 196 * ob2(3) = 2 197 * ob2(4) = 2 198 * ob2(5) = 3 199 * ... and so on. 200 */ 201 202 #define order_base_2(n) ilog2(roundup_pow_of_two(n)) 203 204 #endif /* _LINUX_LOG2_H */ 205