Messages in this thread | | | Date | Wed, 5 Nov 2014 16:47:14 +0100 | From | Maxime Coquelin <> | Subject | Re: [PATCH v3] bitops: Fix shift overflow in GENMASK macros |
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On 11/05/2014 12:10 PM, Rasmus Villemoes wrote: > On Tue, Nov 04 2014, Maxime COQUELIN <maxime.coquelin@st.com> 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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