Re: [Intel-gfx] [PATCH v5] overflow: Introduce overflows_type() and castable_to_type()

Kees Cook
2022-11-02T19:33:40Z

On Wed, Nov 02, 2022 at 12:52:32PM +0100, Rasmus Villemoes wrote:
> On 24/10/2022 22.11, Gwan-gyeong Mun wrote:
> > From: Kees Cook <keescook@chromium.org>
> >
> > Implement a robust overflows_type() macro to test if a variable or
> > constant value would overflow another variable or type. This can be
> > used as a constant expression for static_assert() (which requires a
> > constant expression[1][2]) when used on constant values. This must be
> > constructed manually, since __builtin_add_overflow() does not produce
> > a constant expression[3].
> >
> > Additionally adds castable_to_type(), similar to __same_type(), but for
> > checking if a constant value would overflow if cast to a given type.
> >
>
> > +#define __overflows_type_constexpr(x, T) ( \
> > + is_unsigned_type(typeof(x)) ? \
> > + (x) > type_max(typeof(T)) ? 1 : 0 \
> > + : is_unsigned_type(typeof(T)) ? \
> > + (x) < 0 || (x) > type_max(typeof(T)) ? 1 : 0 \
> > + : (x) < type_min(typeof(T)) || \
> > + (x) > type_max(typeof(T)) ? 1 : 0)
> > +
>
> Can't all these instances of "foo ? 1 : 0" be simplified to "foo"? That
> would improve the readability of this thing somewhat IMO.

Oh, good point. :P I'll fix these.

--
Kees Cook