linux-kernel - Re: [PATCH v2 net-next 2/6] bitmap: add a couple more helpers to work with arrays of u32s

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Date:   Thu, 20 Oct 2022 08:31:42 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Alexander Lobakin <alexandr.lobakin@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Michal Swiatkowski <michal.swiatkowski@...ux.intel.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net-next 2/6] bitmap: add a couple more helpers to
 work with arrays of u32s

On Thu, Oct 20, 2022 at 04:18:08PM +0300, Andy Shevchenko wrote:
> On Wed, Oct 19, 2022 at 05:21:01PM -0700, Yury Norov wrote:
> > On Tue, Oct 18, 2022 at 04:00:23PM +0200, Alexander Lobakin wrote:
> 
> ...
> 
> > > +static inline size_t bitmap_arr32_size(size_t nbits)
> > > +{
> > > +	return array_size(BITS_TO_U32(nbits), sizeof(u32));
> > 
> > To me this looks simpler: round_up(nbits, 32) / BITS_PER_BYTE.
> > Can you check which generates better code?
> 
> It's not only about better code, but also about overflow protection, which your
> proposal is missing.

Can you explain how this may overflow?

  #define __round_mask(x, y) ((__typeof__(x))((y)-1))
  #define round_up(x, y) ((((x)-1) | __round_mask(x, y))+1)

Thanks,
Yury