diff options
| author | Robert P. J. Day <rpjday@mindspring.com> | 2007-10-16 23:29:32 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2007-10-17 08:42:56 -0700 |
| commit | b311e921b385b5a848f0806df16276aca1ecae07 (patch) | |
| tree | 957947e319b23150ddbbf7db52f9bdd24b6cdba5 /include/linux | |
| parent | d9aacccf457d07d729cfc7bf20ff0c7428357a9f (diff) | |
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 <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>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/log2.h | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/include/linux/log2.h b/include/linux/log2.h index 1b8a2c1cb0e..c8cf5e8ef17 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 */ |