Re: [RFC][PATCH] new byteorder primitives - ..._{replace,get}_bits()

Al Viro
2017-12-13T00:37:09Z

On Tue, Dec 12, 2017 at 03:59:33PM -0800, Jakub Kicinski wrote:
> > +static __always_inline __##type type##_replace_bits(__##type old, \
> > + base val, base mask) \
> > +{ \
> > + __##type m = to(mask); \
> > + if (__builtin_constant_p(val) && \
>
> Is the lack of a __builtin_constant_p(mask) test intentional? Sometimes
> the bitfield is a packed array and people may have a helper to which
> only the mask is passed as non-constant and the value is implied by the
> helper, thus constant.

If the mask in non-constant, we probably shouldn't be using that at all;
could you show a real-world example where that would be the case?