Re: [PATCH 3/9] bitmap: Use FIELD_PREP() in expansion of FIELD_PREP_WM16()

David Laight
2025-12-09T18:54:55Z

On Tue, 9 Dec 2025 17:46:21 +0200
Andy Shevchenko <andriy.shevchenko@intel.com> wrote:

> On Tue, Dec 09, 2025 at 10:03:07AM +0000, david.laight.linux@gmail.com wrote:
>
> > Instead of directly expanding __BF_FIELD_CHECK() (which really ought
> > not be used outside bitfield) and open-coding the generation of the
> > masked value, just call FIELD_PREP() and add an extra check for
> > the mask being at most 16 bits.
>
> ...
>
> > +#define FIELD_PREP_WM16(mask, val) \
> > +({ \
> > + __auto_type _mask = mask; \
> > + u32 _val = FIELD_PREP(_mask, val); \
>
> > + BUILD_BUG_ON_MSG(_mask > 0xffffu, \
> > + "FIELD_PREP_WM16: mask too large"); \
>
> Can it be static_assert() instead?

No, they have to be 'integer constant expressions' not just
'compile time constants'.
Pretty useless for anything non-trivial.

David

>
> > + _val | (_mask << 16); \
> > +})
>