Re: [PATCH v7 1/4] bitops: Introduce the the for_each_set_clump macro

Andy Shevchenko
2020-05-31T11:01:06Z

On Sun, May 31, 2020 at 4:11 AM Syed Nayyar Waris <syednwaris@gmail.com> wrote:
> On Sat, May 30, 2020 at 2:50 PM Andy Shevchenko
> <andy.shevchenko@gmail.com> wrote:
> > On Sat, May 30, 2020 at 11:45 AM Syed Nayyar Waris <syednwaris@gmail.com> wrote:
> > > On Sat, May 30, 2020 at 3:49 AM Andy Shevchenko
> > > <andy.shevchenko@gmail.com> wrote:

...

> #if (l) == 0
> #define GENMASK_INPUT_CHECK(h, l) 0
> #elif
> #define GENMASK_INPUT_CHECK(h, l) \
> (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> __builtin_constant_p((l) > (h)), (l) > (h), 0)))
> #endif
>
> I have verified that this works. Basically this just avoids the sanity
> check when the 'lower' bound 'l' is zero. Let me know if it looks
> fine.

Unfortunately, it's not enough. We need to take care about the following cases
1) h or l negative;
2) h == 0, if l == 0, I dunno what is this. it's basically either 0 or warning;
3) l == 0;
4) h and l > 0.

Now, on top of that (since it's a macro) we have to keep in mind that
h and l can be signed and / or unsigned types.
And macro shall work for all 4 cases (by type signedess).

> Regarding min, max macro that you suggested I am also looking further into it.

Since this has been introduced in v5.7 and not only your code is
affected by this I think we need to ping original author either to fix
or revert.

So, I Cc'ed to the author and reviewers, because they probably know
better why that had been done in the first place and breaking existing
code.

--
With Best Regards,
Andy Shevchenko