Improve Miller loop performance for SW6

[arkworks-rs]

Improve Miller loop performance for SW6

[yelhousni]

Normally, affine coordinates should yield a faster pairing over SW6 if the inverse is implemented using the norm map as suggested in [1, 2, 3]. But I think it's not the case here, thus the ~4x factor you remarked.

[yelhousni]

Here is a ML in projective coordinates for SW6 curve: https://github.com/EYBlockchain/zk-swap-libff/blob/ey/libff/algebra/curves/sw6/sw6_pairing.cpp and for SW6_BIS (field size of 761 bits): https://github.com/EYBlockchain/zk-swap-libff/blob/ey/libff/algebra/curves/sw6_bis/sw6_bis_pairing.cpp

[Pratyush]

Awesome! Do you mind I port over the implementation to Rust? Is it under the MIT license?

[yelhousni]

Yes, it is MIT you can port it to Rust. I am working btw on porting SW6_BIS to Rust and do a PR here if you want.

[Pratyush]

Yes, that would be great!