linux-kernel - Re: [PATCH] log2.h: Define order_base

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Date:	Sun, 11 Nov 2007 10:28:37 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	"Robert P. J. Day" <rpjday@...shcourse.ca>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>
Subject: Re: [PATCH] log2.h: Define order_base_2() macro for convenience.

On Sat, 10 Nov 2007 22:53:36 -0500 (EST) Robert P. J. Day wrote:

> 
> Given a number of places in the tree that need to calculate this value
> explicitly, might as well just create a macro for it.
> 
> Signed-off-by: Robert P. J. Day <rpjday@...shcourse.ca>
> 
> ---
> 
>   run-time tested for the first several values.  note that this macro
> is defined strictly in terms of rounding *up* -- i've seen no places
> in the tree that require this expression to be rounded down, so i'm
> not drawing that distinction.
> 
> diff --git a/include/linux/log2.h b/include/linux/log2.h
> index c8cf5e8..ed121c0 100644
> --- a/include/linux/log2.h
> +++ b/include/linux/log2.h
> @@ -190,4 +190,20 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
>  	__rounddown_pow_of_two(n)		\
>   )
> 
> +/**
> + * order_base_2 - calculate the (rounded up) base 2 order of the argument
> + * @n - parameter

 * @n: argument

(mostly changing - to :)

> + *
> + * The first few values calculated by this routine:
> + *  ob2(0) = 0
> + *  ob2(1) = 0
> + *  ob2(2) = 1
> + *  ob2(3) = 2
> + *  ob2(4) = 2
> + *  ob2(5) = 3
> + *  ... and so on.
> + */
> +
> +#define order_base_2(n) ilog2(roundup_pow_of_two(n))
> +
>  #endif /* _LINUX_LOG2_H */
> 
> -- 

---
~Randy
-
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