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Add a "rounddown_pow_of_two" routine to log2.h

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To go along with the existing "roundup_pow_of_two" routine, add one for
rounding down since that operation appears to crop up on a regular basis in
the source tree.

[m.kozlowski@tuxland.pl: fix unbalanced parentheses]
Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Robert P. J. Day 2007-10-16 23:29:32 -07:00 committed by Linus Torvalds
parent d9aacccf45
commit b311e921b3
1 changed files with 25 additions and 0 deletions
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25
include/linux/log2.h
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@ -63,6 +63,15 @@ unsigned long __roundup_pow_of_two(unsigned long n)
return 1UL << fls_long(n - 1); 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 * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
* @n - parameter * @n - parameter
@ -165,4 +174,20 @@ unsigned long __roundup_pow_of_two(unsigned long n)
__roundup_pow_of_two(n) \ __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) ? ( \
(n == 1) ? 0 : \
(1UL << ilog2(n))) : \
__rounddown_pow_of_two(n) \
)
#endif /* _LINUX_LOG2_H */ #endif /* _LINUX_LOG2_H */