On Wed, May 23, 2012 at 9:19 AM, Borislav Petkov
<borislav.petkov@xxxxxxx> wrote:
>
> Actually we need a BIT() macro that works both
> on 32- and 64-bit. But that won't be that easy:
We could use __builtin_choose_expr(), but that *only* works with constants.
So we could do this:
static inline unsigned long bit(unsigned int x)
{
return 1ul << x;
}
static inline u64 bit64(unsigned int x)
{
return 1ull << x;
}
#define BIT(x) \
__builtin_choose_expr((x) < 8*sizeof(unsigned long), bit(x), bit64(x))
but then you *have* to use a plain constant for the BIT() macro.
Anything else will error out in a big way. Non-constant users would
have to be modified to use bit() and bit64() instead.
And no, I tested. You apparently can't do
#define __is_longlongshift(x) \
(__builtin_constant_p(x) && (x) < 8*(sizeof(long)))
because while that is a compile-time constant expression, it's not
"constant enough" for __builtin_choose_expr().
Linus
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