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Commit b311e921 authored by Robert P. J. Day's avatar Robert P. J. Day Committed by Linus Torvalds
Browse files

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: default avatarRobert P. J. Day <rpjday@mindspring.com>
Signed-off-by: default avatarMariusz Kozlowski <m.kozlowski@tuxland.pl>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d9aacccf

include/linux/log2.h

+25 −0
Original line number Diff line number Diff line
@@ -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 */