From: Robert P. J. Day Date: Wed, 17 Oct 2007 06:29:32 +0000 (-0700) Subject: Add a "rounddown_pow_of_two" routine to log2.h X-Git-Tag: v2.6.24-rc1~640 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b311e921b385b5a848f0806df16276aca1ecae07;p=linux-2.6 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: Robert P. J. Day Signed-off-by: Mariusz Kozlowski Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/include/linux/log2.h b/include/linux/log2.h index 1b8a2c1cb0..c8cf5e8ef1 100644 --- a/include/linux/log2.h +++ b/include/linux/log2.h @@ -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 */