linux-kernel - Re: [PATCH v12 01/11] bitops: Introduce the for_each_set

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190326031422.GB3356@icarus>
Date:   Tue, 26 Mar 2019 12:14:22 +0900
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     linus.walleij@...aro.org, bgolaszewski@...libre.com,
        akpm@...ux-foundation.org, linux-gpio@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        andriy.shevchenko@...ux.intel.com, linux@...musvillemoes.dk,
        yamada.masahiro@...ionext.com,
        linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
        geert@...ux-m68k.org, preid@...ctromag.com.au,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v12 01/11] bitops: Introduce the for_each_set_clump8 macro

On Mon, Mar 25, 2019 at 10:38:54AM +0100, Lukas Wunner wrote:
> On Mon, Mar 25, 2019 at 03:22:23PM +0900, William Breathitt Gray wrote:
> > +/**
> > + * find_next_clump8 - find next 8-bit clump with set bits in a memory region
> > + * @clump: location to store copy of found clump
> > + * @addr: address to base the search on
> > + * @offset: bit offset at which to start searching
> > + * @size: bitmap size in number of bits
> > + *
> > + * Returns the bit offset for the next set clump; the found clump value is
> > + * copied to the location pointed by @clump. If no bits are set, returns @size.
> > + */
> > +unsigned int find_next_clump8(unsigned long *const clump,
> > +			      const unsigned long *const addr,
> > +			      unsigned int offset, const unsigned int size)
> > +{
> > +	for (; offset < size; offset += 8) {
> > +		*clump = bitmap_get_value8(addr, size, offset);
> > +		if (!*clump)
> > +			continue;
> > +
> > +		return offset;
> > +	}
> > +
> > +	return size;
> > +}
> > +EXPORT_SYMBOL(find_next_clump8);
> 
> Just use find_first_bit() / find_next_bit() to use optimized arch-specific
> bitops instead of open-coding the iteration over the bitmap.
> 
> See max3191x_get_multiple() for an example.
> 
> Thanks,
> 
> Lukas

Is this the sort of implementation you had in mind:

        offset = find_next_bit(addr, size, offset);
        if (offset == size)
                return size;

        offset -= offset % 8;
        *clump = bitmap_get_value8(addr, size, offset);

        return offset;

Yes, this does seem more efficient to leverage the existing
find_next_bit function.

Should the offset and size parameters be redefined as unsigned long to
match the find_first_bit/find_next_bit function parameters?

William Breathitt Gray