Re: [KJ] powers of 2, and the boundary case of zero

[Jaco Kroon <jaco@kroon.co.za>]

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Martin Olsen wrote:

> What do you say to this patch?
> 
> Martin

Circular inclusion protection or multiple inclusion protection at least?

> ------------------------------------------------------------------------
> 
> diff -uprN -X linux-2.6.19-vanilla/Documentation/dontdiff linux-2.6.19-vanilla/include/linux/power_of_2.h linux-2.6.19-changed/include/linux/power_of_2.h
> --- linux-2.6.19-vanilla/include/linux/power_of_2.h	1970-01-01 01:00:00.000000000 +0100
> +++ linux-2.6.19-changed/include/linux/power_of_2.h	2007-01-10 12:42:03.000000000 +0100
> @@ -0,0 +1,20 @@

#ifndef _LINUX_POWER_OF_2_H
#define _LINUX_POWER_OF_2_H

> +static inline bool is_power_of_2(int i)
> +{
> +	return i > 0 && (i & (i - 1)) == 0;
> +}

/* perhaps rather - to be able to get those cases
   where 0 is acceptable as well? */
static inline bool is_power_of_2_or_zero(int i)
{
        return (i & (i - 1)) == 0;
}

static inline bool is_power_of_2(int i)
{
        return i && is_power_of_2_or_zero(i);
}

> +static inline int round_up_to_power_of_2(int i)
> +{
> +	while ((i & (i - 1)) != 0)
> +		i += i & ~(i - 1);
> +	
> +	return i;
> +}
> +
> +static inline int round_down_to_power_of_2(int i)
> +{
> +	while (i & (i - 1))
> +		i &= (i - 1);
> +	
> +	return i;
> +}

#endif

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