linux-kernel - Re: [PATCH] bitmap: simplify GENMASK(size

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Message-ID: <YXkdP/Rr+m30Hh72@smile.fi.intel.com>
Date:   Wed, 27 Oct 2021 12:34:55 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Qian Cai <quic_qiancai@...cinc.com>
Cc:     Yury Norov <yury.norov@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bitmap: simplify GENMASK(size - 1, 0) lines

On Tue, Oct 26, 2021 at 03:33:48PM -0400, Qian Cai wrote:
> On 10/26/21 3:21 PM, Andy Shevchenko wrote:
> > Can you explain to me how it is supposed to work?
> > 
> > For example,
> > 
> >     x = 0xaa55;
> >     size = 5;
> > 
> >     printf("%lu\n", find_first_bit(&x, size));
> > 
> > In the resulting code we will always have 5 as the result,
> > but is it correct one?
> 
> Sorry, my bad. GENMASK(size - 1, 0) would just become __GENMASK(size -
> 1, 0) instead of 0. Let me revisit it and run some tests first.

And we do not want to have __GENMASK() in the code.
Btw, I found one lurking around. Will fix it.

-- 
With Best Regards,
Andy Shevchenko