Convert BigNum to/from integer types

[olehmisar]

Problem

Need to convert BigNum to/from U128 or u8, u16, u32, u64.

Happy Case

Add BigNum::from(x: U128) and U128::from(x: BigNum) via From trait. An error should be thrown if the conversion is invalid (number is too big/too small).

Workaround

None

Workaround Description

No response

Additional Context

No response

Project Impact

Blocker

Blocker Context

No response

Would you like to submit a PR for this Issue?

Maybe

Support Needs

IDK how to convert, so if someone can explain in words/pseudocode, i can submit a PR

[kashbrti]

Hi Oleh, I'm currently writing a from_field method for bignum which should help with this. will send you the PR when it's ready. Other than U128 this should all be pretty straightforward, given bignum limbs are 120-bits long. So for all the types you could just make a field element out of them and create a zero array with your field element in index 0

[olehmisar]

Why a from_field method instead of From::from trait impl?

[kashbrti]

that's what I meant. I'm writing an impl for std::convert::From<Field> for bignum. The rest should be quite straightforward with the field conversion in hand.

[olehmisar]

Good. I specifically need U128 tbh. But it should be convertible using U128::to_integer().into::().

Any chance you can get the conversion from BigNum to Field implemented as well?

[kashbrti]

#87
here's the PR adding the from Field method. It's still WIP, but the logic should be there.