Re: [PATCH v2 08/16] bitfield: Simplify __BF_FIELD_CHECK_REG()

David Laight
2025-12-17T22:31:59Z

On Wed, 17 Dec 2025 10:26:18 +0000
Jonathan Cameron <jonathan.cameron@huawei.com> wrote:

> On Fri, 12 Dec 2025 19:37:13 +0000
> david.laight.linux@gmail.com wrote:
>
> > From: David Laight <david.laight.linux@gmail.com>
> >
> > Simplify the check for 'reg' being large enough to hold 'mask' using
> > sizeof (reg) rather than a convoluted scheme to generate an unsigned
> > type the same size as 'reg'.
> >
> > Signed-off-by: David Laight <david.laight.linux@gmail.com>
> Hi David,
>
> Just one really trivial comment inline. Feel free to ignore.
>
> Jonathan
>
> > ---
> > @@ -75,8 +59,8 @@
> > })
> >
> > #define __BF_FIELD_CHECK_REG(mask, reg, pfx) \
> > - BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) > \
> > - __bf_cast_unsigned(reg, ~0ull), \
> > + BUILD_BUG_ON_MSG((mask) + 0U + 0UL + 0ULL > \
> > + ~0ULL >> (64 - 8 * sizeof (reg)), \
>
> Trivial. sizeof(reg) is much more comment syntax in kernel code.
(common)

Hmm. sizeof is an operator not a function.
Its argument is either a variable/expression or a bracketed type
(I don't usually put variables in brackets).
So 'sizeof(reg)' is nearly as bad as 'return(reg)'.

David

>
> > pfx "type of reg too small for mask")
> >
> > #define __BF_FIELD_CHECK(mask, reg, val, pfx) \
>