Messages in this thread Patch in this message | | | Date | Wed, 29 Aug 2007 04:12:19 -0400 (EDT) | From | "Robert P. J. Day" <> | Subject | [PATCH] 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.
Signed-off-by: Robert P. J. Day <rpjday@mindspring.com>
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some brief tests indicate that these routines return the correct answer. i'm not sure if i've officially submitted this before or if it's already been accepted in a tree somewhere.
diff --git a/include/linux/log2.h b/include/linux/log2.h index 1b8a2c1..ff8835b 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 */ -- ======================================================================== Robert P. J. Day Linux Consulting, Training and Annoying Kernel Pedantry Waterloo, Ontario, CANADA http://crashcourse.ca ======================================================================== - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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