Missing ops about circom-witness-rs HOT 2 OPEN

and Fr_pow

from circom-witness-rs.

@NikZak

A.
To extend the eval functions, we can do the following using ruint library:

1. Fr_neg --> Neg => (M - a) assuming M is the field's order. This has been used to calculate Sub
2. Fr_div --> Div => a.mul_mod (b.inv_mod(M), M) use inv_mod from ruint::algorithms as this uses Extended Euclidean Algorithm to calculate the inverse.
3. Fr_pow --> Pow => a.pow_mod(b, M)

B.
To extend the eval_fr functions, we can do the following:
The Prime Field Fr = Fp256<MontBackend<FrConfig, 4>> elements are implemented using the ark_ff library, which provides functions for calculating negative, division, etc. Adding the following code to the graph.rs file, under the impl Operation -> eval_fr might work :

Neg => a.neg_in_place(),
FromString => Fr::from_str("testString"),
Div => a / b

Source:

1. Ark prime fields library : ark_ff
2. Ark BN254 curve example (similar to ark_bn254 curve used) : curve
3. Arkworks-rs guide
4. Arkworks-rs github

from circom-witness-rs.