netdev - RE: [tcpdump-workers] Modular arithmetic

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Message-ID: <1347269124.1234.1326.camel@edumazet-glaptop>
Date:	Mon, 10 Sep 2012 11:25:24 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	Andi Kleen <ak@...ux.intel.com>,
	George Bakos <gbakos@...inista.org>,
	tcpdump-workers@...ts.tcpdump.org,
	Jay Schulist <jschlst@...ba.org>, netdev@...r.kernel.org
Subject: RE: [tcpdump-workers] Modular arithmetic

On Mon, 2012-09-10 at 09:41 +0100, David Laight wrote:
> > On Fri, Sep 07, 2012 at 07:49:10AM +0000, George Bakos wrote:
> > > Gents,
> > > Any fundamental reason why the following (, etc.) shouldn't be
> > > included in net/core/filter.c?
> > >
> > >                 case BPF_S_ALU_MOD_X:
> > >                         if (X == 0)
> > >                                 return 0;
> > >                         A %= X;
> > >                         continue;
> > 
> > Copying netdev.
> > 
> > In principle no reason against it, but you may need to update
> > the various BPF JITs too that Linux now has too.
> 
> What about the other OS - eg all the BSDs?
> I had a vague idea that BPF was supposed to be reasonable portable.

Yes, does it mean BPF is frozen ?

Or is BSD so hard to update these days ?

modulus can be implemented using fallback to div and sub, I am not sure
libpcap should sense kernel support or not.

George, make sure libpcap optimizer correctly replaces MOD X  by AND (X
- 1) if X is a power of two.



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