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

Rasmus Villemoes
2022-11-04T19:48:48Z

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.

Rasmus