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Message-ID: <ZM1Z/6l6yCaOEjjF@smile.fi.intel.com>
Date: Fri, 4 Aug 2023 23:05:19 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Yury Norov <yury.norov@...il.com>
Cc: Alexander Potapenko <glider@...gle.com>, catalin.marinas@....com,
will@...nel.org, pcc@...gle.com, andreyknvl@...il.com,
linux@...musvillemoes.dk, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, eugenis@...gle.com,
syednwaris@...il.com, william.gray@...aro.org,
Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v4 1/5] lib/bitmap: add bitmap_{set,get}_value()
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
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