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Date:   Fri, 4 Aug 2023 23:05:19 +0300
From:   Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To:     Yury Norov <yury.norov@gmail.com>
Cc:     Alexander Potapenko <glider@google.com>, catalin.marinas@arm.com,
        will@kernel.org, pcc@google.com, andreyknvl@gmail.com,
        linux@rasmusvillemoes.dk, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, eugenis@google.com,
        syednwaris@gmail.com, william.gray@linaro.org,
        Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v4 1/5] lib/bitmap: add bitmap_{set,get}_value()
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On Fri, Aug 04, 2023 at 12:55:01PM -0700, Yury Norov wrote:
> On Fri, Aug 04, 2023 at 06:07:00PM +0200, Alexander Potapenko wrote:

> > > > ~BITMAP_FIRST_WORD_MASK(start));
> > >
> > > As I said, ~BITMAP_FIRST_WORD_MASK() is the same as BITMAP_LAST_WORD_MASK()
> > > and vise-versa.
> > 
> > Surprisingly, ~BITMAP_FIRST_WORD_MASK() generates better code than
> > BITMAP_LAST_WORD_MASK().
>  
> Wow... If that's consistent across different compilers/arches, we'd
> just drop the latter. Thanks for pointing that. I'll check.

It might be...

...

> >         map[index] &= (fit ? (~(GENMASK(nbits - 1, 0) << offset)) :
> > ~BITMAP_FIRST_WORD_MASK(start));

...that both parts of ternary are using negation. So compiler may use negation
only once. (Haven't looked at the assembly.)

-- 
With Best Regards,
Andy Shevchenko