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

[Maxime Coquelin]

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?

Kind regards,
Maxime
> Rasmus

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