Roland Dreier wrote:
>
> > + /* please add new bits here to ensure allocation uniqueness */
> > + BUG_ON(20 != hweight32(
> > + O_RDONLY | O_WRONLY | O_RDWR |
>
> I wonder if there's a way to make this BUILD_BUG_ON(), so the problem is
> caught at compile time (a change like adding an O_ flag is often compile
> tested only for obscure archs). One could create a compile-time
> macro-ized version of hweight32() and use that, I guess, although I'm
> not sure it's worth the ugliness.
Not ugly at all:
#define hweight32(x) __builtin_popcount(x)
Checked GCC 3.4.3 / 4.1 / 4.4: It expands as a compile-time constant
if the argument is a compile-time constant, so can be used in
BUILD_BUG_ON() and even for array sizes etc.
If GCC's __builtin_popcount() isn't good enough for non-constant
values, the macro would be more involved:
#define hweight32(x) (__builtin_constant_p(x) ? __builtin_popcount(x) \
: hweight32_nonconstant(x))
-- Jamie
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
