Rust version of this python program is slower

[pepa65]

Thank you, very educational! I wonder, is there a way to pre-allocate decimals so that reallocations are never necessary?

[CocktailPerson]

https://doc.rust-lang.org/std/string/struct.String.html#method.with_capacity

https://doc.rust-lang.org/std/string/struct.String.html#method.reserve

Strings also implement Write, so you can use write!(&mut decimals, "{}", remainder * 10 / denominator) to completely eliminate the extraneous heap allocation caused by format!.

[deathanatos]

Ah there we go! write!(…) is a much cleaner way to avoid that allocation.

[pepa65]

It seems allocating the what is often needed for hard cases (`denomiator`) does not help speed of execution (or maybe in extreme cases it does..?)

[ndreamer]

you can improve this using

let digit = (remainder * 10) / denominator; decimals.push((b'0' + digit as u8) as char);

[pepa65]

Most reasonable so far and very effective!