Date: Mon, 8 Jun 2015 07:47:47 +0800 From: Erich Dollansky <erichsfreebsdlist@alogt.com> To: Hans Petter Selasky <hps@selasky.org> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@FreeBSD.org> Subject: Re: allow ffs & co. a binary search Message-ID: <20150608074747.55be51c8@B85M-HD3-0.alogt.com> In-Reply-To: <55745D08.5000505@selasky.org> References: <20150607081315.7c0f09fb@B85M-HD3-0.alogt.com> <5573EA5E.40806@selasky.org> <20150607195245.62dc191f@B85M-HD3-0.alogt.com> <55745D08.5000505@selasky.org>
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Hi Hans,
On Sun, 07 Jun 2015 17:02:32 +0200
Hans Petter Selasky <hps@selasky.org> wrote:
> On 06/07/15 13:52, Erich Dollansky wrote:
> > On Sun, 07 Jun 2015 08:53:18 +0200
> > Hans Petter Selasky <hps@selasky.org> wrote:
> >> On 06/07/15 02:13, Erich Dollansky wrote:
> >>> If you like the binary way I could give you the sources for the
> >>> complete family following your style to replace the older
> >>> functions.
> >>>
> >> I think this is not the fastest way to do it. You first find the
> >> LSB,
> >
> > I never thought of this as I took the code a long, long time from
> > university and expanded it over time from 8 to 64 bits.
> >
> >> then you do a sumbits, which doesn't have any conditionals IF/ELSE
> >> and performs better with the CPU pipeline. I think the software
> >> ffs() is only used for platforms which doesn't have a hardware
> >> version btw:
> >
> > The code is not x86 specific.
> >>
> > This one is the same:
> >
> >> From my libmbin:
> >>
> >> int ffs(int value)
> >> {
> >> int retval = mbin_sumbits32(mbin_lsb32(value) - 1);
> >> if (retval == 32)
> >> retval = 0;
> >> else
> >> retval++;
> >> return (retval);
> >> }
> >>
> > Where is this? Should this also be in 10.1?
>
> It is currently nowhere, just in my private SVN. Would you wrap up
> complete patch, and I can put it into Phabricator and let more people
> look at it. Does your patch cover both kernel and userspace?
>
I can do this but will need some help especially in the coding style
department. Can I e-mail the source first to see if it matches the
formal requirements?
> >
> > What I saw is that all CPUs except ARM uses the software version.
>
> Kernel too?
I did not check.
Erich
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