1use ark_ff::PrimeField;
 2use ark_relations::r1cs::SynthesisError;
 3
 4use crate::fields::fp::FpVar;
 5use crate::fields::FieldVar;
 6use ark_std::vec::Vec;
 7
 8/// Stores a polynomial in coefficient form, where coeffcient is represented by a list of `Fpvar<F>`.
 9pub struct DensePolynomialVar<F: PrimeField> {
10    /// The coefficient of `x^i` is stored at location `i` in `self.coeffs`.
11    pub coeffs: Vec<FpVar<F>>,
12}
13
14impl<F: PrimeField> DensePolynomialVar<F> {
15    /// Constructs a new polynomial from a list of coefficients.
16    pub fn from_coefficients_slice(coeffs: &[FpVar<F>]) -> Self {
17        Self::from_coefficients_vec(coeffs.to_vec())
18    }
19
20    /// Constructs a new polynomial from a list of coefficients.
21    pub fn from_coefficients_vec(coeffs: Vec<FpVar<F>>) -> Self {
22        Self { coeffs }
23    }
24
25    /// Evaluates `self` at the given `point` and just gives you the gadget for the result.
26    /// Caution for use in holographic lincheck: The output has 2 entries in one matrix
27    pub fn evaluate(&self, point: &FpVar<F>) -> Result<FpVar<F>, SynthesisError> {
28        let mut result: FpVar<F> = FpVar::zero();
29        // current power of point
30        let mut curr_pow_x: FpVar<F> = FpVar::one();
31        for i in 0..self.coeffs.len() {
32            let term = &curr_pow_x * &self.coeffs[i];
33            result += &term;
34            curr_pow_x *= point;
35        }
36
37        Ok(result)
38    }
39}
40
41#[cfg(test)]
42mod tests {
43    use crate::alloc::AllocVar;
44    use crate::fields::fp::FpVar;
45    use crate::poly::polynomial::univariate::dense::DensePolynomialVar;
46    use crate::R1CSVar;
47    use ark_poly::polynomial::univariate::DensePolynomial;
48    use ark_poly::{Polynomial, UVPolynomial};
49    use ark_relations::r1cs::ConstraintSystem;
50    use ark_std::vec::Vec;
51    use ark_std::{test_rng, UniformRand};
52    use ark_test_curves::bls12_381::Fr;
53
54    #[test]
55    fn test_evaluate() {
56        let mut rng = test_rng();
57        for _ in 0..100 {
58            let cs = ConstraintSystem::new_ref();
59            let poly: DensePolynomial<Fr> = DensePolynomial::rand(10, &mut rng);
60            let poly_var = {
61                let coeff: Vec<_> = poly
62                    .coeffs
63                    .iter()
64                    .map(|&x| FpVar::new_witness(ns!(cs, "coeff"), || Ok(x)).unwrap())
65                    .collect();
66                DensePolynomialVar::from_coefficients_vec(coeff)
67            };
68            let point = Fr::rand(&mut rng);
69            let point_var = FpVar::new_witness(ns!(cs, "point"), || Ok(point)).unwrap();
70
71            let expected = poly.evaluate(&point);
72            let actual = poly_var.evaluate(&point_var).unwrap();
73
74            assert_eq!(actual.value().unwrap(), expected);
75            assert!(cs.is_satisfied().unwrap());
76        }
77    }
78}