Resending this...as I did not get the mail thru KJ...
Robert,
Maybe its late, but I would still like to discuss if it is
needed-is_power_of_2 has '2' and not 'two' which I think is easier to
work with. I was hoping that the 2 macros that you have coded can also
be named with a '2' in them than a 'two'.
There have been many changes that went in already based on these 2
macros.I have the cleanup patches ready(for log2.h AND all the changes
that went in), but my net at home went down, should be up in a few
hours and so i should be able to mail in the cleanups in a few hours.
If you and others feel that the 'two's can be replaced with '2' then I
would push in the patches by tonight.
Vignesh Babu.
On 8/27/07, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote:
>
> Consistent with the existing roundup_pow_of_two() routine, add the
> corresponding rounddown_pow_of_two() routine.
>
> Signed-off-by: Robert P. J. Day <rpjday@xxxxxxxxxxxxxx>
>
> ---
>
> i'm not sure if this has already been accepted into one of the
> preliminary trees, but can someone check that the logic here makes
> sense? i've tested it, and it seems to return the correct results.
>
> and this would certainly allow some existing code to be simplified.
>
>
> 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 */
>
> rday
> --
> ========================================================================
> Robert P. J. Day
> Linux Consulting, Training and Annoying Kernel Pedantry
> Waterloo, Ontario, CANADA
>
> http://crashcourse.ca
> ========================================================================
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