提交 b311e921 编写于 作者: R Robert P. J. Day 提交者: Linus Torvalds

Add a "rounddown_pow_of_two" routine to log2.h

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: NRobert P. J. Day <rpjday@mindspring.com>
Signed-off-by: NMariusz Kozlowski <m.kozlowski@tuxland.pl>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
上级 d9aacccf
......@@ -63,6 +63,15 @@ 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
......@@ -165,4 +174,20 @@ unsigned long __roundup_pow_of_two(unsigned long 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 */
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