tools/include/linux/log2.h

   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 */