Date: Mon, 1 Nov 2004 12:51:43 -0800 (PST)
From: dean gaudet <dean-list-linux-kernel@arctic.org>
To: Marc Bevand <bevand_m@epita.fr>
cc: linux-kernel@vger.kernel.org
Subject: Re: [rc4-amd64] RC4 optimized for AMD64
In-Reply-To: <Pine.LNX.4.61.0411011233203.8483@twinlark.arctic.org>
Message-ID: <Pine.LNX.4.61.0411011249550.25856@twinlark.arctic.org>
References: <cm4moc$c7t$1@sea.gmane.org> <Pine.LNX.4.61.0411011233203.8483@twinlark.arctic.org>
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On Mon, 1 Nov 2004, dean gaudet wrote:

> On Mon, 1 Nov 2004, Marc Bevand wrote:
> 
> > I have just published a small paper about optimizing RC4 for
> > AMD64 (x86-64). A working implementation is also provided:
> > 
> >   http://epita.fr/~bevand_m/papers/rc4-amd64.html
> > 
> > Kernel people may be interested given the fact that Linux
> > already implements RC4.
> 
> you've made a non-portable flags assumption:
> 
> >       dec     %r11b
> >       ror     $8,             %r8             # (ror does not change ZF)
> >       jnz 1b
> 
> the contents of ZF are undefined after a rotation... most importantly 
> they differ between p4 (ZF is set according to result) and k8 (ZF 
> unchanged).

ack... it's too early on a monday morning -- i misread the documentation.  
this ZF assumption is actually defined and portable... still kind of ugly.  
how much benefit do you see?

-dean
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