netdev - RE: [PATCH net-next 09/10] net/mlx4_en: Manage flow steering rules with ethtool

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Date:	Mon, 2 Jul 2012 13:15:12 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Andreas Schwab" <schwab@...ux-m68k.org>
Cc:	"Joe Perches" <joe@...ches.com>,
	"Ben Hutchings" <bhutchings@...arflare.com>,
	"Or Gerlitz" <ogerlitz@...lanox.com>, <davem@...emloft.net>,
	<roland@...nel.org>, <yevgenyp@...lanox.com>, <oren@...lanox.com>,
	<netdev@...r.kernel.org>, "Hadar Hen Zion" <hadarh@...lanox.co.il>
Subject: RE: [PATCH net-next 09/10] net/mlx4_en: Manage flow steering rules with ethtool

 
> "David Laight" <David.Laight@...LAB.COM> writes:
> 
> >  
> >> > Or write it as (!field || !(typeof(field))~field) which more
closely
> >> > resembles what the macro name expresses.
> >> 
> >> Better still, or maybe:
> >> 
> >> 	field == 0 || field == (typeof field)~0
> >
> > Which doesn't work when sizeof(field) > sizeof(int).
> > Needs another cast.
> >
> > 	field == 0 || field == (typeof field)~(typeof field)0
> 
> You can avoid that by using (typeof field)-1.

Gah, I thought I knew the integral promotion rules!
-1 and ~0 are both 'integer' and get treated the same.

A quick test shows that gcc does sign extend when converting
32bit int to 64bit unsigned long long.
Which probably means that is required by the standard!

	David


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