Re: [PATCH 08/22] bitops: introduce MANY_BITS() macro

[Yury Norov]

Hi Max,

On Tue, May 10, 2022 at 10:57:25AM -0700, Max Filippov wrote:
> Hi Yury,
> 
> On Tue, May 10, 2022 at 8:48 AM Yury Norov <yury.norov@xxxxxxxxx> wrote:
> > arch/xtensa/kernel/traps.c and include/linux/log2.h define very similar
> > functions with different behaviour. XTENSA defines IS_POW2(), and
> > log2.h defines is_power_of_2(). The difference is that IS_POW2()
> > considers 0 as power of 2, while is_power_of_2() - does not.
> 
> IS_POW2 is constructed this way because we know that there is at least
> one non-zero bit in the value that it tests.
> 
> > This discrepancy may confuse reader. From mathematical point of view,
> > 0 is not a power of 2.
> 
> If it would reduce the confusion we can add a check that the value is
> non-zero in the IS_POW2 macro.
> 
> I'd really like to not introduce the local macro and just use something
> standard,

This patch introduces a macro MANY_BITS() in include/linux/bitops.h, which
is a full analogue of IS_POW2(). Would it work for you to switch to
MANY_BITS()? 

> but I can't use is_power_of_2 in a preprocessor condition, can I?

I believe you can't.

Thanks,
Yury