linux-kernel - Re: [patch] fix up generic csum_ipv6

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Message-ID: <20061113092515.GS29920@ftp.linux.org.uk>
Date:	Mon, 13 Nov 2006 09:25:15 +0000
From:	Al Viro <viro@....linux.org.uk>
To:	David Miller <davem@...emloft.net>, kenneth.w.chen@...el.com,
	akpm@...l.org, jgarzik@...ox.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [patch] fix up generic csum_ipv6_magic function prototype

On Mon, Nov 13, 2006 at 09:12:22AM +0000, Russell King wrote:
> On Mon, Nov 13, 2006 at 08:52:23AM +0000, Al Viro wrote:
> > After doing the above we have the following:
> > 
> > Platform-dependent:
> > __wsum csum_tcpudp_nofold(__be32, __be32, T1, T2, __wsum);
> > On arm/arm26: T1 = unsigned short, T2 = unsigned int.
> > __sum16 csum_tcpudp_magic(__be32, __be32, unsigned short, T, __wsum);
> > On arm/arm26 T is unsigned int, elsewhere it's unsigned short.
> 
> Could both become unsigned short or unsigned int.  Would prefer
> unsigned int on ARM, since otherwise the compiler generate code to
> truncate any variable "int"s to an unsigned short.

Frankly, as for the generated code...  I'd expect s/htons(len)/len * 256/
and the same for proto in there to have much more effect.  And it does give
the same checksum...
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