On Wed, May 23, 2012 at 09:57:47AM -0700, Linus Torvalds wrote:
> On Wed, May 23, 2012 at 9:53 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> >
> > How about the following completely untested chunk:
>
> No, you can't do that. All standard C operations will return *one*
> type. That very much includes the ternary ?: operator.
And, in addition, hpa's example won't work too:
u64 msr = ~BIT(1);
> The *only* ways I know of to get two types are
>
> - C preprocessor stuff, ie
>
> #define BIT(x) __BIT_##x
>
> and then just enumerate all the 64 cases. This is portable, but it gets old.
Nah, that's ugly.
> - using __builtin_choose_expr(), which actually allows the two
> expressions to have different types, but requires a very strict
> compile-time constant (ie you cannot rely on the optimizer making it a
> constant - because it needs to choose the expression before the
> optimizer runs)
>
> There might be some other magic gcc extension, of course.
Hmm and if not, it looks like BIT_64 is the easiest and most readable
thing we can do.
Oh well.
--
Regards/Gruss,
Boris.
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