1use ark_ec::AffineRepr;
 2use ark_std::ops::Add;
 3use std::marker::PhantomData;
 4
 5use crate::pedersen::Commitment;
 6use crate::r1cs::*;
 7use crate::transcript::Transcript;
 8use crate::utils::*;
 9
10// Phi: φ in the paper (later 𝖴), a folded instance
11pub struct Phi<C: AffineRepr> {
12    cmE: Commitment<C>,
13    u: C::ScalarField,
14    cmW: Commitment<C>,
15    x: Vec<C::ScalarField>,
16}
17
18// FWit: Folded Witness
19pub struct FWit<C: AffineRepr> {
20    E: Vec<C::ScalarField>,
21    rE: C::ScalarField,
22    W: Vec<C::ScalarField>,
23    rW: C::ScalarField,
24}
25
26pub struct NIFS<C: AffineRepr> {
27    _phantom: PhantomData<C>,
28}
29
30impl<C: AffineRepr> NIFS<C> {
31    pub fn fold_witness(
32        r: C::ScalarField,
33        fw1: FWit<C>,
34        fw2: FWit<C>,
35        T: Vec<C::ScalarField>,
36    ) -> FWit<C> {
37        let r2 = r * r;
38        let E: Vec<C::ScalarField> = vec_add(
39            // TODO this syntax will be simplified with future operators impl
40            vec_add(fw1.E, vector_elem_product(&T, &r)),
41            vector_elem_product(&fw2.E, &r2),
42        );
43        let rE = fw1.rE + r * fw2.rE;
44        let W = vec_add(fw1.W, vector_elem_product(&fw2.W, &r));
45        let rW = fw1.rW + r * fw2.rW;
46        FWit::<C> {
47            E: E.into(),
48            rE,
49            W: W.into(),
50            rW,
51        }
52    }
53
54    pub fn fold_instance(
55        r: C::ScalarField,
56        phi1: Phi<C>,
57        phi2: Phi<C>,
58        cmT: Commitment<C>,
59    ) -> Phi<C> {
60        let r2 = r * r;
61
62        let cmE = phi1.cmE.cm + cmT.cm.mul(r) + phi2.cmE.cm.mul(r2);
63        let u = phi1.u + r * phi2.u;
64        let cmW = phi1.cmW.cm + phi2.cmW.cm.mul(r);
65        let x = vec_add(phi1.x, vector_elem_product(&phi2.x, &r));
66
67        Phi::<C> {
68            cmE: Commitment::<C> {
69                cm: cmE.into(),
70                r: phi1.cmE.r,
71            },
72            u,
73            cmW: Commitment::<C> {
74                cm: cmW.into(),
75                r: phi1.cmW.r,
76            },
77            x,
78        }
79    }
80}