https://onlinedocs.microchip.com/oxy/GUID-317042D4-BCCE-4065...

https://www.nongnu.org/avr-libc/user-manual/group__avr__stdl...

https://manpages.debian.org/testing/avr-libc/ultoa.3avr.en.h...

https://www.ibm.com/docs/en/zos/2.4.0?topic=functions-utoa-c...

https://www.qnx.com/developers/docs/6.3.2/neutrino/lib_ref/u...

Here is the documentation for the problem you mentioned.