1use tensor_pcs::EqPoly;
 2
 3use crate::FieldExt;
 4
 5#[derive(Clone, Debug)]
 6pub struct MlPoly<F> {
 7    pub evals: Vec<F>,
 8    pub num_vars: usize,
 9}
10
11impl<F: FieldExt> MlPoly<F> {
12    pub fn new(evals: Vec<F>) -> Self {
13        assert!(evals.len().is_power_of_two());
14        let num_vars = (evals.len() as f64).log2() as usize;
15        Self { evals, num_vars }
16    }
17
18    fn dot_prod(x: &[F], y: &[F]) -> F {
19        assert_eq!(x.len(), y.len());
20        let mut result = F::ZERO;
21        for i in 0..x.len() {
22            result += x[i] * y[i];
23        }
24        result
25    }
26
27    // Evaluate the multilinear extension of the polynomial `a`, at point `t`.
28    // `a` is in evaluation form.
29    // `t` should be in big-endian form.
30    pub fn eval(&self, t: &[F]) -> F {
31        let n = self.evals.len();
32        debug_assert_eq!((n as f64).log2() as usize, t.len());
33
34        let eq_evals = EqPoly::new(t.to_vec()).evals();
35
36        Self::dot_prod(&self.evals, &eq_evals)
37    }
38}
39
40#[cfg(test)]
41mod tests {
42    use super::*;
43    type F = halo2curves::secp256k1::Fp;
44    use halo2curves::ff::Field;
45
46    #[test]
47    fn test_ml_poly_eval() {
48        let num_vars = 4;
49        let num_evals = 2usize.pow(num_vars as u32);
50        let evals = (0..num_evals)
51            .map(|x| F::from(x as u64))
52            .collect::<Vec<F>>();
53
54        let ml_poly = MlPoly::new(evals.clone());
55        let eval_last = ml_poly.eval(&[F::ONE, F::ONE, F::ONE, F::ONE]);
56        assert_eq!(
57            eval_last,
58            evals[evals.len() - 1],
59            "The last evaluation is not correct"
60        );
61
62        let eval_first = ml_poly.eval(&[F::ZERO, F::ZERO, F::ZERO, F::ZERO]);
63        assert_eq!(eval_first, evals[0], "The first evaluation is not correct");
64
65        let eval_second = ml_poly.eval(&[F::ZERO, F::ZERO, F::ZERO, F::ONE]);
66        assert_eq!(
67            eval_second, evals[1],
68            "The second evaluation is not correct"
69        );
70    }
71}