On Mon, Jun 27, 2022 at 12:05 PM Luc Van Oostenryck
<luc.vanoostenryck@xxxxxxxxx> wrote:
>
> #define is_signed_type(type) (((type)-1) <= 0)
Side note: the reason we *don't* use this form in the kernel is
because broken compilers will complain about compares with zero in
unsigned types.
Using "<=" like you do may be an acceptable way to avoid it (the most
obvious thing is to use "< 0"), but it makes me nervous.
Regardless, I think you need the cast of the zero. I think "type"
might be a pointer, and sparse should be complaining about the horrid
use of a bare 0 as NULL.
Similar issues might happen for enums, where various compilers will
complain about comparing an enum to a non-enum.
So I'm pretty sure you would want casts on both values, instead of
assuming "it's an integer type, I don't need to cast 0".
But yeah, maybe
#define is_signed_type(type) (((type)-1) <= (type)0)
works fine and avoids warnings in all the cases.
Famous last words. Warnings can happen for almost anything, and I
wonder if that use of "1" had some other reason.
Linus
