linux-kernel - RE: [PATCH v4 1/1] drm/i915: Move abs

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] [day] [month] [year] [list]

Message-ID: <7c1885528d474c719bb4d4e0cf985753@AcuMS.aculab.com>
Date:   Fri, 4 Aug 2023 15:50:18 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andrew Morton' <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC:     Jani Nikula <jani.nikula@...el.com>,
        Imre Deak <imre.deak@...el.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Andi Shyti <andi.shyti@...ux.intel.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        "Helge Deller" <deller@....de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: RE: [PATCH v4 1/1] drm/i915: Move abs_diff() to math.h

From: Andrew Morton
> Sent: 03 August 2023 18:25
> 
> On Thu,  3 Aug 2023 16:19:18 +0300 Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> 
> > abs_diff() belongs to math.h. Move it there.
> > This will allow others to use it.
> >
> > ...
> >
> > --- a/include/linux/math.h
> > +++ b/include/linux/math.h
> > @@ -155,6 +155,13 @@ __STRUCT_FRACT(u32)
> >  	__builtin_types_compatible_p(typeof(x), unsigned type),		\
> >  	({ signed type __x = (x); __x < 0 ? -__x : __x; }), other)
> >
> > +#define abs_diff(a, b) ({			\
> > +	typeof(a) __a = (a);			\
> > +	typeof(b) __b = (b);			\
> > +	(void)(&__a == &__b);			\
> > +	__a > __b ? (__a - __b) : (__b - __a);	\
> > +})
> 
> Can we document it please?
> 
> Also, the open-coded type comparison could be replaced with __typecheck()?
> 
> And why the heck isn't __typecheck() in typecheck.h, to be included by
> minmax.h.

And why would you want to use __typecheck() anyway?
It pretty much isn't the test you are looking for.
If you are trying to explicitly avoid converting negative value
to large positive unsigned ones then you want something like:
	is_signed_type(typeof(a)) == is_signed_type(typeof(b))
but it isn't even that simple :-)

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)