Add a "rounddown_pow_of_two" routine to log2.h (b311e921) · Commits · 戴 / test

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>

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 */

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