linux-kernel - Re: [PATCH 1/1] unify DMA_..BIT

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Date:	Fri, 5 Oct 2007 15:24:50 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	schwab@...e.de, rpjday@...dspring.com, bbpetkov@...oo.de,
	linux-kernel@...r.kernel.org, muli@...ibm.com,
	satyam@...radead.org, amitkale@...xen.com,
	achim_leubner@...ptec.com
Subject: Re: [PATCH 1/1] unify DMA_..BIT_MASK definitions: v3.1

On Fri, 05 Oct 2007 14:28:45 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Andreas Schwab wrote:
> > #define DMA_BIT_MASK(n)         ((u64)-1 >> (64 - (n)))
> >   
> 
> Yeah, that's cleaner.
> 

Well yes, but DMA_BIT_MASK(0) invokes undefined behaviour, generates a
compiler warning and evaluates to 0xffffffffffffffff (with my setup).

That won't be a problem in practice, but it is strictly wrong and doesn't set
a good exmaple for the children ;)

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