On Tue, Dec 17 2024, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> Instead of dealing with all the different special types (size_t,
> unsigned char, ptrdiff_t..) just deal with the size of the integer type
> and the sign.
>
> This avoids a lot of unnecessary case statements, and the games we play
> with the value of the 'SIGN' flags value
>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> ---
>
> NOTE! Only very lightly tested. Also meant to be purely preparatory.
> It might be broken.
>
> I started doing this in the hope that the vsnprintf() core code could
> maybe be further cleaned up enough that it would actually be something
> we could use more generally and export to other users that want to
> basically do the printk format handling.
>
> The code is *not* there yet, though. Small steps.
>
> +/* Turn a 1/2/4-byte value into a 64-bit one with sign handling */
> +static unsigned long long get_num(unsigned int val, struct printf_spec spec)
> +{
> + unsigned int shift = 32 - spec.type*8;
> +
> + val <<= shift;
> + if (!(spec.flags & SIGN))
> + return val >> shift;
> + return (int)val >> shift;
> +}
> +
I think this needs to be a little more explicit that it's not just about
handling sign extension, but also truncation to the desired
width. Otherwise somebody will wonder why this isn't
if (!(spec.flags & SIGN))
return val;
return (int)(val << shift) >> shift;
[with the latter line duplicating our sign_extend32 helper].
The rest looks good.
Rasmus
