linux-kernel - Re: [PATCH v2 18/20] linux/power_of_2.h: Add __IS_POWER_OF_2(n) and __IS_POWER_OF_2_OR

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Date:   Mon, 22 Nov 2021 10:55:28 +0200
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Arnd Bergmann <arnd@...db.de>,
        Alejandro Colomar <alx.manpages@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Kees Cook <keescook@...omium.org>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v2 18/20] linux/power_of_2.h: Add __IS_POWER_OF_2(n) and
 __IS_POWER_OF_2_OR_0(n) macros

On Sun, 21 Nov 2021, Arnd Bergmann <arnd@...db.de> wrote:
> On Sat, Nov 20, 2021 at 2:01 PM Alejandro Colomar
> <alx.manpages@...il.com> wrote:
>> +
>> +#define __IS_POWER_OF_2_OR_0(n)  (((n) & ((n) - 1)) == 0)
>> +#define __IS_POWER_OF_2(n)       (__IS_POWER_OF_2_OR_0(n) && ((n) != 0))
>> +
>
> There is already is_power_of_2() in include/linux/log2.h, which would
> be preferred
> in most cases. If you need a macro version, put it in the same file
> and explain why it's
> needed.

Also, the macro argument n is evaluated 2-3 times. Please use
checkpatch.pl --strict argument on the patches, and it'll give you hints
about this stuff too.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center