Re: [PATCH 1/1] unify DMA_..BIT_MASK definitions: v3.1

Andrew Morton
2007-10-05T22:25:27Z

On Fri, 05 Oct 2007 14:28:45 -0700
Jeremy Fitzhardinge <jeremy@goop.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 ;)