Add conversion from eval form to coeff form

src/poly/multivariate.rs

@@ -1,39 +1,33 @@
-use std::fmt::Debug;
 use ff::Field;
+use rayon::prelude::{IntoParallelIterator, ParallelIterator};
+use std::fmt::Debug;
 
-/// [coeff, deg(x_1), ..., deg(x_n)]
-#[derive(Debug, Clone)]
-struct Term<F: Field>(Vec<F>);
-
-/// num_vars: number of variables
-/// coefficients: [[coeff, deg(x_1), ..., deg(x_n)], ...] respectively
-#[derive(Clone, Debug)]
-struct CoefficientForm<F: Field> {
-    num_vars: u32,
-    coefficients: Vec<Term<F>>,
+#[derive(Debug)]
+pub struct MultilinearPolynomial<F> {
+    coeffs: Vec<F>,
+    num_vars: usize,
 }
 
-/// format: f(g(h(..)))
-/// outer: f
-/// inner: g(..)
-#[derive(Debug, Clone)]
-struct CompositionForm {
-}
+// #[derive(Debug, Clone)]
+// pub enum MultivariatePolynomial<F: Field> {
+//     Coeff(CoefficientForm<F>),
+// }
 
-#[derive(Debug, Clone)]
-struct FactoredForm<F: Field> {
-    terms: Vec<Vec<Term<F>>>,
-}
+impl<F: Field> MultilinearPolynomial<F> {
+    fn new(coeffs: Vec<F>, num_vars: usize) -> Self {
+        MultilinearPolynomial { coeffs, num_vars }
+    }
 
-#[derive(Debug, Clone)]
-pub enum MultivariatePolynomial<F: Field> {
-    Coeff(CoefficientForm<F>),
-    Comp(CompositionForm),
-    Fac(FactoredForm<F>),
-}
-
-impl<F: Field> MultivariatePolynomial<F>  {
-    fn interpolate(points: Vec<F>, k: u32) -> Self {
-        todo!()
+    fn eval_to_coeff(poly: &[F], num_vars: usize) -> MultilinearPolynomial<F> {
+        let mut result = poly.to_vec();
+        for i in (0..num_vars).rev() {
+            let chunk_size = 2usize.pow((i + 1) as u32);
+            for chunk_offset in (0..poly.len()).step_by(chunk_size) {
+                for j in chunk_offset..(chunk_offset + chunk_size / 2) {
+                    result[j + chunk_size / 2] -= poly[j];
+                }
+            }
+        }
+        Self::new(result, num_vars)
     }
 }