linux-kernel - Re: [PATCH] Add "is_power_of

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Message-ID: <45BF3954.8050106@yahoo.com.au>
Date:	Tue, 30 Jan 2007 23:25:56 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	"Robert P. J. Day" <rpjday@...dspring.com>
CC:	Linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	Paul Mackerras <paulus@...ba.org>, dhowells@...hat.com,
	galak@...nel.crashing.org
Subject: Re: [PATCH] Add "is_power_of_2" checking to log2.h.

Robert P. J. Day wrote:
>   Add the inline function "is_power_of_2()" to log2.h, where the value
> zero is *not* considered to be a power of two.

> 
> Signed-off-by: Robert P. J. Day <rpjday@...dspring.com>
> 
>  /*
> + *  Determine whether some value is a power of two, where zero is
> + * *not* considered a power of two.
> + */

Why the qualifier? Zero *is* not a power of 2, is it?

> +
> +static inline __attribute__((const))
> +bool is_power_of_2(unsigned long n)
> +{
> +	return (n != 0 && ((n & (n - 1)) == 0));
> +}
> +
> +/*
>   * round up to nearest power of two
>   */
>  static inline __attribute__((const))


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