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//! A polynomial represented in evaluations form over a domain of size 2^n.

use super::domain::EvaluationDomain;
use super::polynomial::Polynomial;
use core::ops::{Add, AddAssign, DivAssign, Index, Mul, MulAssign, Sub, SubAssign};
use dusk_bls12_381::Scalar;

/// Stores a polynomial in evaluation form.
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct Evaluations {
    /// The evaluations of a polynomial over the domain `D`
    pub evals: Vec<Scalar>,
    #[doc(hidden)]
    domain: EvaluationDomain,
}

impl Evaluations {
    /// Construct `Self` from evaluations and a domain.
    pub fn from_vec_and_domain(evals: Vec<Scalar>, domain: EvaluationDomain) -> Self {
        Self { evals, domain }
    }

    /// Interpolate a polynomial from a list of evaluations
    pub fn interpolate_by_ref(&self) -> Polynomial {
        Polynomial::from_coefficients_vec(self.domain.ifft(&self.evals))
    }

    /// Interpolate a polynomial from a list of evaluations
    pub fn interpolate(self) -> Polynomial {
        let Self { mut evals, domain } = self;
        domain.ifft_in_place(&mut evals);
        Polynomial::from_coefficients_vec(evals)
    }
}

impl Index<usize> for Evaluations {
    type Output = Scalar;

    fn index(&self, index: usize) -> &Scalar {
        &self.evals[index]
    }
}

impl<'a, 'b> Mul<&'a Evaluations> for &'b Evaluations {
    type Output = Evaluations;

    #[inline]
    fn mul(self, other: &'a Evaluations) -> Evaluations {
        let mut result = self.clone();
        result *= other;
        result
    }
}

impl<'a> MulAssign<&'a Evaluations> for Evaluations {
    #[inline]
    fn mul_assign(&mut self, other: &'a Evaluations) {
        assert_eq!(self.domain, other.domain, "domains are unequal");
        self.evals
            .iter_mut()
            .zip(&other.evals)
            .for_each(|(a, b)| *a *= b);
    }
}

impl<'a, 'b> Add<&'a Evaluations> for &'b Evaluations {
    type Output = Evaluations;

    #[inline]
    fn add(self, other: &'a Evaluations) -> Evaluations {
        let mut result = self.clone();
        result += other;
        result
    }
}

impl<'a> AddAssign<&'a Evaluations> for Evaluations {
    #[inline]
    fn add_assign(&mut self, other: &'a Evaluations) {
        assert_eq!(self.domain, other.domain, "domains are unequal");
        self.evals
            .iter_mut()
            .zip(&other.evals)
            .for_each(|(a, b)| *a += b);
    }
}

impl<'a, 'b> Sub<&'a Evaluations> for &'b Evaluations {
    type Output = Evaluations;

    #[inline]
    fn sub(self, other: &'a Evaluations) -> Evaluations {
        let mut result = self.clone();
        result -= other;
        result
    }
}

impl<'a> SubAssign<&'a Evaluations> for Evaluations {
    #[inline]
    fn sub_assign(&mut self, other: &'a Evaluations) {
        assert_eq!(self.domain, other.domain, "domains are unequal");
        self.evals
            .iter_mut()
            .zip(&other.evals)
            .for_each(|(a, b)| *a -= b);
    }
}

impl<'a> DivAssign<&'a Evaluations> for Evaluations {
    #[inline]
    fn div_assign(&mut self, other: &'a Evaluations) {
        assert_eq!(self.domain, other.domain, "domains are unequal");
        self.evals
            .iter_mut()
            .zip(&other.evals)
            .for_each(|(a, b)| *a *= b.invert().unwrap());
    }
}