RE: [PATCH v4 1/1] drm/i915: Move abs_diff() to math.h
From: Andrew Morton
> Sent: 03 August 2023 18:25
>
> On Thu, 3 Aug 2023 16:19:18 +0300 Andy Shevchenko
> wrote:
>
> > abs_diff() belongs to math.h. Move it there.
> > This will allow others to use it.
> >
> > ...
> >
> > --- a/include/linux/math.h
> > +++ b/include/linux/math.h
> > @@ -155,6 +155,13 @@ __STRUCT_FRACT(u32)
> > __builtin_types_compatible_p(typeof(x), unsigned type), \
> > ({ signed type __x = (x); __x < 0 ? -__x : __x; }), other)
> >
> > +#define abs_diff(a, b) ({ \
> > + typeof(a) __a = (a);\
> > + typeof(b) __b = (b);\
> > + (void)(&__a == &__b); \
> > + __a > __b ? (__a - __b) : (__b - __a); \
> > +})
>
> Can we document it please?
>
> Also, the open-coded type comparison could be replaced with __typecheck()?
>
> And why the heck isn't __typecheck() in typecheck.h, to be included by
> minmax.h.
And why would you want to use __typecheck() anyway?
It pretty much isn't the test you are looking for.
If you are trying to explicitly avoid converting negative value
to large positive unsigned ones then you want something like:
is_signed_type(typeof(a)) == is_signed_type(typeof(b))
but it isn't even that simple :-)
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT,
UK
Registration No: 1397386 (Wales)
Re: [PATCH v4 1/1] drm/i915: Move abs_diff() to math.h
On Thu, Aug 03, 2023 at 10:24:46AM -0700, Andrew Morton wrote:
> On Thu, 3 Aug 2023 16:19:18 +0300 Andy Shevchenko
> wrote:
...
> > +#define abs_diff(a, b) ({ \
> > + typeof(a) __a = (a);\
> > + typeof(b) __b = (b);\
> > + (void)(&__a == &__b); \
> > + __a > __b ? (__a - __b) : (__b - __a); \
> > +})
>
> Can we document it please?
>
> Also, the open-coded type comparison could be replaced with __typecheck()?
>
> And why the heck isn't __typecheck() in typecheck.h, to be included by
> minmax.h.
>
> etcetera. Sigh. I'll grab it, but please at least send along some
> kerneldoc?
Sure and thank you!
--
With Best Regards,
Andy Shevchenko
Re: [PATCH v4 1/1] drm/i915: Move abs_diff() to math.h
On Thu, 3 Aug 2023 16:19:18 +0300 Andy Shevchenko
wrote:
> abs_diff() belongs to math.h. Move it there.
> This will allow others to use it.
>
> ...
>
> --- a/include/linux/math.h
> +++ b/include/linux/math.h
> @@ -155,6 +155,13 @@ __STRUCT_FRACT(u32)
> __builtin_types_compatible_p(typeof(x), unsigned type), \
> ({ signed type __x = (x); __x < 0 ? -__x : __x; }), other)
>
> +#define abs_diff(a, b) ({\
> + typeof(a) __a = (a);\
> + typeof(b) __b = (b);\
> + (void)(&__a == &__b); \
> + __a > __b ? (__a - __b) : (__b - __a); \
> +})
Can we document it please?
Also, the open-coded type comparison could be replaced with __typecheck()?
And why the heck isn't __typecheck() in typecheck.h, to be included by
minmax.h.
etcetera. Sigh. I'll grab it, but please at least send along some
kerneldoc?
