[Feature request] Add support for i128 and u128

[Munksgaard]

Since both Rust and Elixir have support for 128-bit sized integers (i128, u128, erlang) it seems natural that Rustler should support it as well.

I have a specific use case for i128s as well, which is implementing support for the Decimal type from Polars in Explorer.

[Munksgaard]

I can't really figure out if this is going to be a problem, but at least it's something to be aware of.

[evnu]

Would this work for you: https://github.com/rusterlium/rustler/tree/master/rustler_bigint ?

[filmor]

I can't really figure out if this is going to be a problem, but at least it's something to be aware of.

I don't think this is relevant for Rustler. It would be, if the NIF API actually included (C-based) support for 128-bit integer types, but it only supports up to 64.

If someone wants to work on this, https://github.com/rusterlium/rustler/tree/master/rustler_bigint can be taken as a basis. While that library is more general and implements support for arbitrarily-sized integers, the same approach (going via the term_to_binary) can be used for the standard library types i128 and u128.

[Munksgaard]

I have not had time to look at the bigint library yet, but it indeed seems like the easiest way to handle something like this.

[filmor]

Implemented in #600.

[Munksgaard]

Incredible! Thank you for your work @filmor!