linux/include/linux/log2.h
<<
>>
Prefs
   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 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public License
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the License, or (at your option) any later version.
  10 */
  11
  12#ifndef _LINUX_LOG2_H
  13#define _LINUX_LOG2_H
  14
  15#include <linux/types.h>
  16#include <linux/bitops.h>
  17
  18/*
  19 * deal with unrepresentable constant logarithms
  20 */
  21extern __attribute__((const, noreturn))
  22int ____ilog2_NaN(void);
  23
  24/*
  25 * non-constant log of base 2 calculators
  26 * - the arch may override these in asm/bitops.h if they can be implemented
  27 *   more efficiently than using fls() and fls64()
  28 * - the arch is not required to handle n==0 if implementing the fallback
  29 */
  30#ifndef CONFIG_ARCH_HAS_ILOG2_U32
  31static inline __attribute__((const))
  32int __ilog2_u32(u32 n)
  33{
  34        return fls(n) - 1;
  35}
  36#endif
  37
  38#ifndef CONFIG_ARCH_HAS_ILOG2_U64
  39static inline __attribute__((const))
  40int __ilog2_u64(u64 n)
  41{
  42        return fls64(n) - 1;
  43}
  44#endif
  45
  46/*
  47 *  Determine whether some value is a power of two, where zero is
  48 * *not* considered a power of two.
  49 */
  50
  51static inline __attribute__((const))
  52bool is_power_of_2(unsigned long n)
  53{
  54        return (n != 0 && ((n & (n - 1)) == 0));
  55}
  56
  57/*
  58 * round up to nearest power of two
  59 */
  60static inline __attribute__((const))
  61unsigned long __roundup_pow_of_two(unsigned long n)
  62{
  63        return 1UL << fls_long(n - 1);
  64}
  65
  66/*
  67 * round down to nearest power of two
  68 */
  69static inline __attribute__((const))
  70unsigned long __rounddown_pow_of_two(unsigned long n)
  71{
  72        return 1UL << (fls_long(n) - 1);
  73}
  74
  75/**
  76 * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
  77 * @n - parameter
  78 *
  79 * constant-capable log of base 2 calculation
  80 * - this can be used to initialise global variables from constant data, hence
  81 *   the massive ternary operator construction
  82 *
  83 * selects the appropriately-sized optimised version depending on sizeof(n)
  84 */
  85#define ilog2(n)                                \
  86(                                               \
  87        __builtin_constant_p(n) ? (             \
  88                (n) < 1 ? ____ilog2_NaN() :     \
  89                (n) & (1ULL << 63) ? 63 :       \
  90                (n) & (1ULL << 62) ? 62 :       \
  91                (n) & (1ULL << 61) ? 61 :       \
  92                (n) & (1ULL << 60) ? 60 :       \
  93                (n) & (1ULL << 59) ? 59 :       \
  94                (n) & (1ULL << 58) ? 58 :       \
  95                (n) & (1ULL << 57) ? 57 :       \
  96                (n) & (1ULL << 56) ? 56 :       \
  97                (n) & (1ULL << 55) ? 55 :       \
  98                (n) & (1ULL << 54) ? 54 :       \
  99                (n) & (1ULL << 53) ? 53 :       \
 100                (n) & (1ULL << 52) ? 52 :       \
 101                (n) & (1ULL << 51) ? 51 :       \
 102                (n) & (1ULL << 50) ? 50 :       \
 103                (n) & (1ULL << 49) ? 49 :       \
 104                (n) & (1ULL << 48) ? 48 :       \
 105                (n) & (1ULL << 47) ? 47 :       \
 106                (n) & (1ULL << 46) ? 46 :       \
 107                (n) & (1ULL << 45) ? 45 :       \
 108                (n) & (1ULL << 44) ? 44 :       \
 109                (n) & (1ULL << 43) ? 43 :       \
 110                (n) & (1ULL << 42) ? 42 :       \
 111                (n) & (1ULL << 41) ? 41 :       \
 112                (n) & (1ULL << 40) ? 40 :       \
 113                (n) & (1ULL << 39) ? 39 :       \
 114                (n) & (1ULL << 38) ? 38 :       \
 115                (n) & (1ULL << 37) ? 37 :       \
 116                (n) & (1ULL << 36) ? 36 :       \
 117                (n) & (1ULL << 35) ? 35 :       \
 118                (n) & (1ULL << 34) ? 34 :       \
 119                (n) & (1ULL << 33) ? 33 :       \
 120                (n) & (1ULL << 32) ? 32 :       \
 121                (n) & (1ULL << 31) ? 31 :       \
 122                (n) & (1ULL << 30) ? 30 :       \
 123                (n) & (1ULL << 29) ? 29 :       \
 124                (n) & (1ULL << 28) ? 28 :       \
 125                (n) & (1ULL << 27) ? 27 :       \
 126                (n) & (1ULL << 26) ? 26 :       \
 127                (n) & (1ULL << 25) ? 25 :       \
 128                (n) & (1ULL << 24) ? 24 :       \
 129                (n) & (1ULL << 23) ? 23 :       \
 130                (n) & (1ULL << 22) ? 22 :       \
 131                (n) & (1ULL << 21) ? 21 :       \
 132                (n) & (1ULL << 20) ? 20 :       \
 133                (n) & (1ULL << 19) ? 19 :       \
 134                (n) & (1ULL << 18) ? 18 :       \
 135                (n) & (1ULL << 17) ? 17 :       \
 136                (n) & (1ULL << 16) ? 16 :       \
 137                (n) & (1ULL << 15) ? 15 :       \
 138                (n) & (1ULL << 14) ? 14 :       \
 139                (n) & (1ULL << 13) ? 13 :       \
 140                (n) & (1ULL << 12) ? 12 :       \
 141                (n) & (1ULL << 11) ? 11 :       \
 142                (n) & (1ULL << 10) ? 10 :       \
 143                (n) & (1ULL <<  9) ?  9 :       \
 144                (n) & (1ULL <<  8) ?  8 :       \
 145                (n) & (1ULL <<  7) ?  7 :       \
 146                (n) & (1ULL <<  6) ?  6 :       \
 147                (n) & (1ULL <<  5) ?  5 :       \
 148                (n) & (1ULL <<  4) ?  4 :       \
 149                (n) & (1ULL <<  3) ?  3 :       \
 150                (n) & (1ULL <<  2) ?  2 :       \
 151                (n) & (1ULL <<  1) ?  1 :       \
 152                (n) & (1ULL <<  0) ?  0 :       \
 153                ____ilog2_NaN()                 \
 154                                   ) :          \
 155        (sizeof(n) <= 4) ?                      \
 156        __ilog2_u32(n) :                        \
 157        __ilog2_u64(n)                          \
 158 )
 159
 160/**
 161 * roundup_pow_of_two - round the given value up to nearest power of two
 162 * @n - parameter
 163 *
 164 * round the given value up 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 roundup_pow_of_two(n)                   \
 169(                                               \
 170        __builtin_constant_p(n) ? (             \
 171                (n == 1) ? 1 :                  \
 172                (1UL << (ilog2((n) - 1) + 1))   \
 173                                   ) :          \
 174        __roundup_pow_of_two(n)                 \
 175 )
 176
 177/**
 178 * rounddown_pow_of_two - round the given value down to nearest power of two
 179 * @n - parameter
 180 *
 181 * round the given value down to the nearest power of two
 182 * - the result is undefined when n == 0
 183 * - this can be used to initialise global variables from constant data
 184 */
 185#define rounddown_pow_of_two(n)                 \
 186(                                               \
 187        __builtin_constant_p(n) ? (             \
 188                (1UL << ilog2(n))) :            \
 189        __rounddown_pow_of_two(n)               \
 190 )
 191
 192/**
 193 * order_base_2 - calculate the (rounded up) base 2 order of the argument
 194 * @n: parameter
 195 *
 196 * The first few values calculated by this routine:
 197 *  ob2(0) = 0
 198 *  ob2(1) = 0
 199 *  ob2(2) = 1
 200 *  ob2(3) = 2
 201 *  ob2(4) = 2
 202 *  ob2(5) = 3
 203 *  ... and so on.
 204 */
 205
 206#define order_base_2(n) ilog2(roundup_pow_of_two(n))
 207
 208#endif /* _LINUX_LOG2_H */
 209
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.