# Release 4.14 tools/include/linux/log2.h

```/* Integer base 2 logarithm calculation
*
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* 2 of the License, or (at your option) any later version.
*/

#ifndef _TOOLS_LINUX_LOG2_H

#define _TOOLS_LINUX_LOG2_H

#include <linux/bitops.h>
#include <linux/types.h>

/*
* non-constant log of base 2 calculators
* - the arch may override these in asm/bitops.h if they can be implemented
*   more efficiently than using fls() and fls64()
* - the arch is not required to handle n==0 if implementing the fallback
*/
static inline __attribute__((const))

int __ilog2_u32(u32 n)
{
return fls(n) - 1;
}

static inline __attribute__((const))

int __ilog2_u64(u64 n)
{
return fls64(n) - 1;
}

/*
*  Determine whether some value is a power of two, where zero is
* *not* considered a power of two.
*/

static inline __attribute__((const))

bool is_power_of_2(unsigned long n)
{
return (n != 0 && ((n & (n - 1)) == 0));
}

/*
* round up to nearest power of two
*/
static inline __attribute__((const))

unsigned long __roundup_pow_of_two(unsigned long n)
{
return 1UL << fls_long(n - 1);
}

/*
* round down to nearest power of two
*/
static inline __attribute__((const))

unsigned long __rounddown_pow_of_two(unsigned long n)
{
return 1UL << (fls_long(n) - 1);
}

/**
* ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
* @n - parameter
*
* constant-capable log of base 2 calculation
* - this can be used to initialise global variables from constant data, hence
*   the massive ternary operator construction
*
* selects the appropriately-sized optimised version depending on sizeof(n)
*/

#define ilog2(n)				\
(                                               \
__builtin_constant_p(n) ? (             \
(n) < 2 ? 0 :                   \
(n) & (1ULL << 63) ? 63 :       \
(n) & (1ULL << 62) ? 62 :       \
(n) & (1ULL << 61) ? 61 :       \
(n) & (1ULL << 60) ? 60 :       \
(n) & (1ULL << 59) ? 59 :       \
(n) & (1ULL << 58) ? 58 :       \
(n) & (1ULL << 57) ? 57 :       \
(n) & (1ULL << 56) ? 56 :       \
(n) & (1ULL << 55) ? 55 :       \
(n) & (1ULL << 54) ? 54 :       \
(n) & (1ULL << 53) ? 53 :       \
(n) & (1ULL << 52) ? 52 :       \
(n) & (1ULL << 51) ? 51 :       \
(n) & (1ULL << 50) ? 50 :       \
(n) & (1ULL << 49) ? 49 :       \
(n) & (1ULL << 48) ? 48 :       \
(n) & (1ULL << 47) ? 47 :       \
(n) & (1ULL << 46) ? 46 :       \
(n) & (1ULL << 45) ? 45 :       \
(n) & (1ULL << 44) ? 44 :       \
(n) & (1ULL << 43) ? 43 :       \
(n) & (1ULL << 42) ? 42 :       \
(n) & (1ULL << 41) ? 41 :       \
(n) & (1ULL << 40) ? 40 :       \
(n) & (1ULL << 39) ? 39 :       \
(n) & (1ULL << 38) ? 38 :       \
(n) & (1ULL << 37) ? 37 :       \
(n) & (1ULL << 36) ? 36 :       \
(n) & (1ULL << 35) ? 35 :       \
(n) & (1ULL << 34) ? 34 :       \
(n) & (1ULL << 33) ? 33 :       \
(n) & (1ULL << 32) ? 32 :       \
(n) & (1ULL << 31) ? 31 :       \
(n) & (1ULL << 30) ? 30 :       \
(n) & (1ULL << 29) ? 29 :       \
(n) & (1ULL << 28) ? 28 :       \
(n) & (1ULL << 27) ? 27 :       \
(n) & (1ULL << 26) ? 26 :       \
(n) & (1ULL << 25) ? 25 :       \
(n) & (1ULL << 24) ? 24 :       \
(n) & (1ULL << 23) ? 23 :       \
(n) & (1ULL << 22) ? 22 :       \
(n) & (1ULL << 21) ? 21 :       \
(n) & (1ULL << 20) ? 20 :       \
(n) & (1ULL << 19) ? 19 :       \
(n) & (1ULL << 18) ? 18 :       \
(n) & (1ULL << 17) ? 17 :       \
(n) & (1ULL << 16) ? 16 :       \
(n) & (1ULL << 15) ? 15 :       \
(n) & (1ULL << 14) ? 14 :       \
(n) & (1ULL << 13) ? 13 :       \
(n) & (1ULL << 12) ? 12 :       \
(n) & (1ULL << 11) ? 11 :       \
(n) & (1ULL << 10) ? 10 :       \
(n) & (1ULL <<  9) ?  9 :       \
(n) & (1ULL <<  8) ?  8 :       \
(n) & (1ULL <<  7) ?  7 :       \
(n) & (1ULL <<  6) ?  6 :       \
(n) & (1ULL <<  5) ?  5 :       \
(n) & (1ULL <<  4) ?  4 :       \
(n) & (1ULL <<  3) ?  3 :       \
(n) & (1ULL <<  2) ?  2 :       \
1 ) :                           \
(sizeof(n) <= 4) ?                      \
__ilog2_u32(n) :                        \
__ilog2_u64(n)                          \
)

/**
* roundup_pow_of_two - round the given value up to nearest power of two
* @n - parameter
*
* round the given value up to the nearest power of two
* - the result is undefined when n == 0
* - this can be used to initialise global variables from constant data
*/

#define roundup_pow_of_two(n)			\
(                                               \
__builtin_constant_p(n) ? (             \
(n == 1) ? 1 :                  \
(1UL << (ilog2((n) - 1) + 1))   \
) :          \
__roundup_pow_of_two(n)                 \
)

/**
* rounddown_pow_of_two - round the given value down to nearest power of two
* @n - parameter
*
* round the given value down to the nearest power of two
* - the result is undefined when n == 0
* - this can be used to initialise global variables from constant data
*/

#define rounddown_pow_of_two(n)			\
(                                               \
__builtin_constant_p(n) ? (             \
(1UL << ilog2(n))) :            \
__rounddown_pow_of_two(n)               \
)

#endif /* _TOOLS_LINUX_LOG2_H */
Overall ContributorsPersonTokensPropCommitsCommitPropArnaldo Carvalho de Melo17299.42%480.00%
Linus Torvalds10.58%120.00%
Total173100.00%5100.00%
Directory: tools/include/linux

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```
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