Re: [PATCH 1/1] unify DMA_..BIT_MASK definitions: v3.1
From: Andrew Morton
Date: Fri Oct 05 2007 - 18:25:29 EST
On Fri, 05 Oct 2007 14:28:45 -0700
Jeremy Fitzhardinge <jeremy@xxxxxxxx> 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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