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 * SPDX-License-Identifier: GPL-2.0+ 7 */ 8 9 #ifndef _LINUX_LOG2_H 10 #define _LINUX_LOG2_H 11 12 #include <linux/types.h> 13 #include <linux/bitops.h> 14 15 /* 16 * deal with unrepresentable constant logarithms 17 */ 18 extern __attribute__((const, noreturn)) 19 int ____ilog2_NaN(void); 20 21 /* 22 * non-constant log of base 2 calculators 23 * - the arch may override these in asm/bitops.h if they can be implemented 24 * more efficiently than using fls() and fls64() 25 * - the arch is not required to handle n==0 if implementing the fallback 26 */ 27 #ifndef CONFIG_ARCH_HAS_ILOG2_U32 28 static inline __attribute__((const)) 29 int __ilog2_u32(u32 n) 30 { 31 return fls(n) - 1; 32 } 33 #endif 34 35 #ifndef CONFIG_ARCH_HAS_ILOG2_U64 36 static inline __attribute__((const)) 37 int __ilog2_u64(u64 n) 38 { 39 return fls64(n) - 1; 40 } 41 #endif 42 43 /* 44 * Determine whether some value is a power of two, where zero is 45 * *not* considered a power of two. 46 */ 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 * round up to nearest power of two 56 */ 57 static inline __attribute__((const)) 58 unsigned long __roundup_pow_of_two(unsigned long n) 59 { 60 return 1UL << fls_long(n - 1); 61 } 62 63 /* 64 * round down to nearest power of two 65 */ 66 static inline __attribute__((const)) 67 unsigned long __rounddown_pow_of_two(unsigned long n) 68 { 69 return 1UL << (fls_long(n) - 1); 70 } 71 72 /** 73 * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value 74 * @n - parameter 75 * 76 * constant-capable log of base 2 calculation 77 * - this can be used to initialise global variables from constant data, hence 78 * the massive ternary operator construction 79 * 80 * selects the appropriately-sized optimised version depending on sizeof(n) 81 */ 82 #define ilog2(n) \ 83 ( \ 84 __builtin_constant_p(n) ? ( \ 85 (n) < 1 ? ____ilog2_NaN() : \ 86 (n) & (1ULL << 63) ? 63 : \ 87 (n) & (1ULL << 62) ? 62 : \ 88 (n) & (1ULL << 61) ? 61 : \ 89 (n) & (1ULL << 60) ? 60 : \ 90 (n) & (1ULL << 59) ? 59 : \ 91 (n) & (1ULL << 58) ? 58 : \ 92 (n) & (1ULL << 57) ? 57 : \ 93 (n) & (1ULL << 56) ? 56 : \ 94 (n) & (1ULL << 55) ? 55 : \ 95 (n) & (1ULL << 54) ? 54 : \ 96 (n) & (1ULL << 53) ? 53 : \ 97 (n) & (1ULL << 52) ? 52 : \ 98 (n) & (1ULL << 51) ? 51 : \ 99 (n) & (1ULL << 50) ? 50 : \ 100 (n) & (1ULL << 49) ? 49 : \ 101 (n) & (1ULL << 48) ? 48 : \ 102 (n) & (1ULL << 47) ? 47 : \ 103 (n) & (1ULL << 46) ? 46 : \ 104 (n) & (1ULL << 45) ? 45 : \ 105 (n) & (1ULL << 44) ? 44 : \ 106 (n) & (1ULL << 43) ? 43 : \ 107 (n) & (1ULL << 42) ? 42 : \ 108 (n) & (1ULL << 41) ? 41 : \ 109 (n) & (1ULL << 40) ? 40 : \ 110 (n) & (1ULL << 39) ? 39 : \ 111 (n) & (1ULL << 38) ? 38 : \ 112 (n) & (1ULL << 37) ? 37 : \ 113 (n) & (1ULL << 36) ? 36 : \ 114 (n) & (1ULL << 35) ? 35 : \ 115 (n) & (1ULL << 34) ? 34 : \ 116 (n) & (1ULL << 33) ? 33 : \ 117 (n) & (1ULL << 32) ? 32 : \ 118 (n) & (1ULL << 31) ? 31 : \ 119 (n) & (1ULL << 30) ? 30 : \ 120 (n) & (1ULL << 29) ? 29 : \ 121 (n) & (1ULL << 28) ? 28 : \ 122 (n) & (1ULL << 27) ? 27 : \ 123 (n) & (1ULL << 26) ? 26 : \ 124 (n) & (1ULL << 25) ? 25 : \ 125 (n) & (1ULL << 24) ? 24 : \ 126 (n) & (1ULL << 23) ? 23 : \ 127 (n) & (1ULL << 22) ? 22 : \ 128 (n) & (1ULL << 21) ? 21 : \ 129 (n) & (1ULL << 20) ? 20 : \ 130 (n) & (1ULL << 19) ? 19 : \ 131 (n) & (1ULL << 18) ? 18 : \ 132 (n) & (1ULL << 17) ? 17 : \ 133 (n) & (1ULL << 16) ? 16 : \ 134 (n) & (1ULL << 15) ? 15 : \ 135 (n) & (1ULL << 14) ? 14 : \ 136 (n) & (1ULL << 13) ? 13 : \ 137 (n) & (1ULL << 12) ? 12 : \ 138 (n) & (1ULL << 11) ? 11 : \ 139 (n) & (1ULL << 10) ? 10 : \ 140 (n) & (1ULL << 9) ? 9 : \ 141 (n) & (1ULL << 8) ? 8 : \ 142 (n) & (1ULL << 7) ? 7 : \ 143 (n) & (1ULL << 6) ? 6 : \ 144 (n) & (1ULL << 5) ? 5 : \ 145 (n) & (1ULL << 4) ? 4 : \ 146 (n) & (1ULL << 3) ? 3 : \ 147 (n) & (1ULL << 2) ? 2 : \ 148 (n) & (1ULL << 1) ? 1 : \ 149 (n) & (1ULL << 0) ? 0 : \ 150 ____ilog2_NaN() \ 151 ) : \ 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 /** 190 * order_base_2 - calculate the (rounded up) base 2 order of the argument 191 * @n: parameter 192 * 193 * The first few values calculated by this routine: 194 * ob2(0) = 0 195 * ob2(1) = 0 196 * ob2(2) = 1 197 * ob2(3) = 2 198 * ob2(4) = 2 199 * ob2(5) = 3 200 * ... and so on. 201 */ 202 203 #define order_base_2(n) ilog2(roundup_pow_of_two(n)) 204 205 #endif /* _LINUX_LOG2_H */ 206