Switch to a more general supraseal_c2::generate_groth16_proofs interface.

[dot-asm]

Verified to work in supranational/supra_seal#39

[vmx]

The CI failure is unrelated. I'm working on fixing it.

[vmx]

@dot-asm I dared to rebase your PR on current master and push it. It should now pass the CI.

[vmx]

Sorry for taking so long for the review. The general change looks good to me (it's much nicer code than the old one). I've just two minor things, see the inline comments.

[vmx]

As the n isn't used anywhere else, I'd just move the provers[0].a.len(); directly into the assert_eq below.

[dot-asm]

A fixup commit is pushed.

[dot-asm]

Sorry for taking so long for the review.

No need to apologize, I understand :-)

[vmx]

Somehow one of my comments didn't make it to GitHub, so let's try it again:

In Rust you usually implement From instead of Into. Quoting the From documentation:

One should always prefer implementing From over Into because implementing From automatically provides one with an implementation of Into thanks to the blanket implementation in the standard library.

I would also move it to the top-level and not inside the function.

As I needed to try it you myself if it actually work, here's the code:

impl<Scalar> From<&ProvingAssignment<Scalar>> for supraseal_c2::Assignment<Scalar>
where
    Scalar: PrimeField,
{
    fn from(assignment: &ProvingAssignment<Scalar>) -> Self {
        assert_eq!(assignment.a.len(), assignment.b.len());
        assert_eq!(assignment.a.len(), assignment.c.len());

        Self {
            a_aux_density: assignment.a_aux_density.bv.as_raw_slice().as_ptr(),
            a_aux_bit_len: assignment.a_aux_density.bv.len(),
            a_aux_popcount: assignment.a_aux_density.get_total_density(),

            b_inp_density: assignment.b_input_density.bv.as_raw_slice().as_ptr(),
            b_inp_bit_len: assignment.b_input_density.bv.len(),
            b_inp_popcount: assignment.b_input_density.get_total_density(),

            b_aux_density: assignment.b_aux_density.bv.as_raw_slice().as_ptr(),
            b_aux_bit_len: assignment.b_aux_density.bv.len(),
            b_aux_popcount: assignment.b_aux_density.get_total_density(),

            a: assignment.a.as_ptr(),
            b: assignment.b.as_ptr(),
            c: assignment.c.as_ptr(),
            abc_size: assignment.a.len(),

            inp_assignment_data: assignment.input_assignment.as_ptr(),
            inp_assignment_size: assignment.input_assignment.len(),

            aux_assignment_data: assignment.aux_assignment.as_ptr(),
            aux_assignment_size: assignment.aux_assignment.len(),
        }
    }
}

[dot-asm]

Fixed up. (Please excuse my distrust for compilers, expressed as preference to give the compiler exactly as much as required, it's kind of an occupational hazard:-)

[DrPeterVanNostrand]

Hi @dot-asm, the From interface looks good to me (and I think the rest of the code too), but just to verify that I understand the PR... this change allows each witness assignment to carry unique denisity trackers, whereas previously, all witnesses were required to have their densities be constructed in an identical fashion?

[dot-asm]

this change allows each witness assignment to carry unique denisity trackers, whereas previously, all witnesses were required to have their densities be constructed in an identical fashion?

Well, the original goal was to streamline the interface and implementation, and the recognition that independent densities would be effectively free was kind of a collateral. Secondly, upon cutting the supraseal-c2 crate the original interface, the one this PR switches from, is just an adapter on top of the new interface, the one this PR switches to. So it's also kind of a cut-out-the-middle-man situation going on here.

[DrPeterVanNostrand]

@dot-asm Cool, thanks for the background info. The PR looks good to me