On Thu, Mar 7, 2019 at 10:17 AM Robin Murphy <[email protected]> wrote: > On 2019-03-07 8:52 am, Arnd Bergmann wrote: > > > > -#define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1)) > > +/* double shift to work around https://bugs.llvm.org/show_bug.cgi?id=38789 > > */ > > +#define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<((n)-1))<<1)-1) > > I think that now makes DMA_BIT_MASK(0) undefined - that shouldn't matter > in most cases, but it could potentially happen at runtime where callers > use a non-constant argument. However, it also means we don't need to > special-case 64 any more (since that's there to avoid the same thing > anyway), so we could simply flip that to handle 0 instead.
Yes, good idea. > FWIW I'd be very tempted to fold in the second shift as "2ULL<<((n)-1)", > but that may not be to everyone's taste. I like that. So shall we do this? /* * Shifting '2' instead of '1' because of * https://bugs.llvm.org/show_bug.cgi?id=38789 */ #define DMA_BIT_MASK(n) (((n) == 0) ? 0ULL : ((2ULL<<((n)-1)))-1) Arnd
