Would allocating a 640-byte string initially really be the right tradeoff? It seems like it could result in a lot of memory overhead if many small strings are created that don’t need that space. But it does save a copy at least

As for the int-to-string function, using the division result to do a faster modulus (eg with the div function) and possibly a lookup table seem like they’d help (there must be some good open source libraries focused on this to look at).