python3 int <-> num_bigint support

[programmerjake]

See also #124

[Askaholic]

I implemented this for grins a while ago: https://gitlab.com/Askaholic/pyrusty.

However, it was my experience that the rust extension module using BigInt was noticeably slower than the python big integer implementation. I was testing this using the baby step giant step algorithm for finding a discrete logarithm.

[programmerjake]

I implemented this for grins a while ago: https://gitlab.com/Askaholic/pyrusty.

However, it was my experience that the rust extension module using BigInt was noticeably slower than the python big integer implementation. I was testing this using the baby step giant step algorithm for finding a discrete logarithm.

I would guess python is faster because it optimises for single-word numbers, whereas BigInt doesn't really (it uses Vec internally instead of something like SmallVec)

[programmerjake]

See also: rust-num/num-bigint#36