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 _TOOLS_LINUX_LOG2_H 9 #define _TOOLS_LINUX_LOG2_H 10 11 #include <linux/bitops.h> 12 #include <linux/types.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 static inline __attribute__((const)) 21 int __ilog2_u32(u32 n) 22 { 23 return fls(n) - 1; 24 } 25 26 static inline __attribute__((const)) 27 int __ilog2_u64(u64 n) 28 { 29 return fls64(n) - 1; 30 } 31 32 /* 33 * Determine whether some value is a power of two, where zero is 34 * *not* considered a power of two. 35 */ 36 37 static inline __attribute__((const)) 38 bool is_power_of_2(unsigned long n) 39 { 40 return (n != 0 && ((n & (n - 1)) == 0)); 41 } 42 43 /* 44 * round up to nearest power of two 45 */ 46 static inline __attribute__((const)) 47 unsigned long __roundup_pow_of_two(unsigned long n) 48 { 49 return 1UL << fls_long(n - 1); 50 } 51 52 /* 53 * round down to nearest power of two 54 */ 55 static inline __attribute__((const)) 56 unsigned long __rounddown_pow_of_two(unsigned long n) 57 { 58 return 1UL << (fls_long(n) - 1); 59 } 60 61 /** 62 * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value 63 * @n - parameter 64 * 65 * constant-capable log of base 2 calculation 66 * - this can be used to initialise global variables from constant data, hence 67 * the massive ternary operator construction 68 * 69 * selects the appropriately-sized optimised version depending on sizeof(n) 70 */ 71 #define ilog2(n) \ 72 ( \ 73 __builtin_constant_p(n) ? ( \ 74 (n) < 2 ? 0 : \ 75 (n) & (1ULL << 63) ? 63 : \ 76 (n) & (1ULL << 62) ? 62 : \ 77 (n) & (1ULL << 61) ? 61 : \ 78 (n) & (1ULL << 60) ? 60 : \ 79 (n) & (1ULL << 59) ? 59 : \ 80 (n) & (1ULL << 58) ? 58 : \ 81 (n) & (1ULL << 57) ? 57 : \ 82 (n) & (1ULL << 56) ? 56 : \ 83 (n) & (1ULL << 55) ? 55 : \ 84 (n) & (1ULL << 54) ? 54 : \ 85 (n) & (1ULL << 53) ? 53 : \ 86 (n) & (1ULL << 52) ? 52 : \ 87 (n) & (1ULL << 51) ? 51 : \ 88 (n) & (1ULL << 50) ? 50 : \ 89 (n) & (1ULL << 49) ? 49 : \ 90 (n) & (1ULL << 48) ? 48 : \ 91 (n) & (1ULL << 47) ? 47 : \ 92 (n) & (1ULL << 46) ? 46 : \ 93 (n) & (1ULL << 45) ? 45 : \ 94 (n) & (1ULL << 44) ? 44 : \ 95 (n) & (1ULL << 43) ? 43 : \ 96 (n) & (1ULL << 42) ? 42 : \ 97 (n) & (1ULL << 41) ? 41 : \ 98 (n) & (1ULL << 40) ? 40 : \ 99 (n) & (1ULL << 39) ? 39 : \ 100 (n) & (1ULL << 38) ? 38 : \ 101 (n) & (1ULL << 37) ? 37 : \ 102 (n) & (1ULL << 36) ? 36 : \ 103 (n) & (1ULL << 35) ? 35 : \ 104 (n) & (1ULL << 34) ? 34 : \ 105 (n) & (1ULL << 33) ? 33 : \ 106 (n) & (1ULL << 32) ? 32 : \ 107 (n) & (1ULL << 31) ? 31 : \ 108 (n) & (1ULL << 30) ? 30 : \ 109 (n) & (1ULL << 29) ? 29 : \ 110 (n) & (1ULL << 28) ? 28 : \ 111 (n) & (1ULL << 27) ? 27 : \ 112 (n) & (1ULL << 26) ? 26 : \ 113 (n) & (1ULL << 25) ? 25 : \ 114 (n) & (1ULL << 24) ? 24 : \ 115 (n) & (1ULL << 23) ? 23 : \ 116 (n) & (1ULL << 22) ? 22 : \ 117 (n) & (1ULL << 21) ? 21 : \ 118 (n) & (1ULL << 20) ? 20 : \ 119 (n) & (1ULL << 19) ? 19 : \ 120 (n) & (1ULL << 18) ? 18 : \ 121 (n) & (1ULL << 17) ? 17 : \ 122 (n) & (1ULL << 16) ? 16 : \ 123 (n) & (1ULL << 15) ? 15 : \ 124 (n) & (1ULL << 14) ? 14 : \ 125 (n) & (1ULL << 13) ? 13 : \ 126 (n) & (1ULL << 12) ? 12 : \ 127 (n) & (1ULL << 11) ? 11 : \ 128 (n) & (1ULL << 10) ? 10 : \ 129 (n) & (1ULL << 9) ? 9 : \ 130 (n) & (1ULL << 8) ? 8 : \ 131 (n) & (1ULL << 7) ? 7 : \ 132 (n) & (1ULL << 6) ? 6 : \ 133 (n) & (1ULL << 5) ? 5 : \ 134 (n) & (1ULL << 4) ? 4 : \ 135 (n) & (1ULL << 3) ? 3 : \ 136 (n) & (1ULL << 2) ? 2 : \ 137 1 ) : \ 138 (sizeof(n) <= 4) ? \ 139 __ilog2_u32(n) : \ 140 __ilog2_u64(n) \ 141 ) 142 143 /** 144 * roundup_pow_of_two - round the given value up to nearest power of two 145 * @n - parameter 146 * 147 * round the given value up to the nearest power of two 148 * - the result is undefined when n == 0 149 * - this can be used to initialise global variables from constant data 150 */ 151 #define roundup_pow_of_two(n) \ 152 ( \ 153 __builtin_constant_p(n) ? ( \ 154 (n == 1) ? 1 : \ 155 (1UL << (ilog2((n) - 1) + 1)) \ 156 ) : \ 157 __roundup_pow_of_two(n) \ 158 ) 159 160 /** 161 * rounddown_pow_of_two - round the given value down to nearest power of two 162 * @n - parameter 163 * 164 * round the given value down to the nearest power of two 165 * - the result is undefined when n == 0 166 * - this can be used to initialise global variables from constant data 167 */ 168 #define rounddown_pow_of_two(n) \ 169 ( \ 170 __builtin_constant_p(n) ? ( \ 171 (1UL << ilog2(n))) : \ 172 __rounddown_pow_of_two(n) \ 173 ) 174 175 #endif /* _TOOLS_LINUX_LOG2_H */ 176