Re: [PATCH v3] bitops: Fix shift overflow in GENMASK macros

[Maxime Coquelin]

On 11/05/2014 05:44 PM, Peter Zijlstra wrote:
> On Wed, Nov 05, 2014 at 04:47:14PM +0100, Maxime Coquelin wrote:
> > On 11/05/2014 12:10 PM, Rasmus Villemoes wrote:
> > > On Tue, Nov 04 2014, Maxime COQUELIN <maxime.coquelin@xxxxxx> wrote:
> > >
> > > > -#define GENMASK(h, l)		(((U32_C(1) << ((h) - (l) + 1)) - 1) << (l))
> > > > -#define GENMASK_ULL(h, l)	(((U64_C(1) << ((h) - (l) + 1)) - 1) << (l))
> > > > +#define GENMASK(h, l) \
> > > > +	((~0UL >> (BITS_PER_LONG - ((h) - (l) + 1))) << (l))
> > > > +
> > > > +#define GENMASK_ULL(h, l) \
> > > > +	((~0ULL >> (BITS_PER_LONG_LONG - ((h) - (l) + 1))) << (l))
> > > Slightly bikeshedding here, but may I suggest spelling it
> > >
> > >    (((~0UL) << (l)) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
> > >
> > > ? This will ensure the arguments are expanded once each, and will, IMHO,
> > > DTRT if/when l > h (namely, yield 0).
> > That's a good point.
> >
> > Peter, what is your view?
> I'm fine with that, feel free to post another version and I'll replace
> v3.

Thanks Peter, v4 just sent.

Regards,
Maxime
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