isascii(3) macros and casts

[Paul Eggert]

On 2024-12-11 11:36, Florian Weimer wrote:
> The table lookups for isdigit and isxdigit are unnecessary.

Thanks for mentioning this - I didn't know it.

Should glibc optimize isdigit into a single subtract + compare at the 
machine level? Something like the following, say?

   #define isdigit(x) ((int) {x} - '0' <= 9u)

(The "(int) {x}" avoids problems that would be caused by casting x.)

This would be significantly more efficient than the current implementation.


Also, portable code should beware that mingw and MSVC do not conform to 
this part of the C standard: in some locales isdigit returns nonzero for 
arguments that are not ASCII digits, e.g., superscript two (0xB2) in 
code page 1252.

I added a note to the Gnulib documentation about this:

https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=9780a7b22b53b3785a1e3bca848a8d90bd2e977e