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From: Phil Sutter <phil@nwl.cc>
To: Florian Westphal <fw@strlen.de>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>, netfilter-devel@vger.kernel.org
Subject: Re: [conntrack-tools PATCH] conntrack: Fix CIDR to mask conversion on Big Endian
Date: Wed, 4 Sep 2019 11:31:14 +0200	[thread overview]
Message-ID: <20190904093114.GI25650@orbyte.nwl.cc> (raw)
In-Reply-To: <20190904082128.GG13660@breakpoint.cc>

Hi,

On Wed, Sep 04, 2019 at 10:21:28AM +0200, Florian Westphal wrote:
> Phil Sutter <phil@nwl.cc> wrote:
> > What we need in b is 'ff ff ff 00' for a prefix length of 24. Your
> > suggested alternative does not compile, so I tried both options for the
> > closing brace:
> > 
> > | htonl((1 << 24) - 1)
> > 
> > This turns into '00 ff ff ff' for both LE and BE, the opposite of what
> > we need.
> > 
> > | htonl((1 << 24)) - 1
> > 
> > This turns into '00 00 00 00' on LE and '00 ff ff ff' on BE.
> > 
> > My code leads to correct result on either architecture and I don't see a
> > simpler way of doing it.
> 
> htonl(~0u << (32 - i)) would work, assuming i > 0 and <= 32.

Ah, indeed! Left-shifting all-ones didn't come to mind. I'll send a v2.

Thanks, Phil

      reply	other threads:[~2019-09-04  9:31 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-02 16:44 [conntrack-tools PATCH] conntrack: Fix CIDR to mask conversion on Big Endian Phil Sutter
2019-09-03 20:34 ` Pablo Neira Ayuso
2019-09-04  6:53   ` Phil Sutter
2019-09-04  8:21     ` Florian Westphal
2019-09-04  9:31       ` Phil Sutter [this message]

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