From: "Robert P. J. Day" 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 Signed-off-by: Andrew Morton --- include/linux/log2.h | 25 +++++++++++++++++++++++++ 1 files changed, 25 insertions(+) diff -puN include/linux/log2.h~add-a-rounddown_pow_of_two-routine-to-log2h include/linux/log2.h --- a/include/linux/log2.h~add-a-rounddown_pow_of_two-routine-to-log2h +++ a/include/linux/log2.h @@ -63,6 +63,15 @@ unsigned long __roundup_pow_of_two(unsig 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(unsig __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 */ _