Information for combine ZPrize

zprize_combine.rs

fn combine(
  g1: &[ark_pallas::Affine],
  g2: &[ark_pallas::Affine],
  chal: &[bool]) -> Vec<ark_pallas::Affine> {
    let c = endo_challenge_to_field(chal);
    g1.iter().zip(g2.iter()).map(|(p1, p2)| p1 + &p2.mul(c))
    .collect()
}

fn endo_challenge_to_field(chal: &[bool]) -> ark_pallas::Affine::ScalarField {
    let length_in_bits: u64 = 128;

    let mut a: F = 2_u64.into();
    let mut b: F = 2_u64.into();

    let one = F::one();
    let neg_one = -one;

    for i in (0..(length_in_bits / 2)).rev() {
        a.double_in_place();
        b.double_in_place();

        let s = if chal[2 * i] == false { &neg_one } else { &one };

        if chal[2 * i + 1] == false {
            b += s;
        } else {
            a += s;
        }
    }

    // endo_coeff is 0x397E65A7D7C1AD71AEE24B27E308F0A61259527EC1D4752E619D1840AF55F1B1
    // or in decimal, 26005156700822196841419187675678338661165322343552424574062261873906994770353
    a * endo_coeff + b
}