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Refactor lagrange_interpolate() method

Browse source 
Co-authored-by: daira <daira@electriccoin.co>
Co-authored-by: str4d <jack@z.cash>
This commit is contained in:
therealyingtong 2020-10-08 22:59:55 +08:00
parent 1441193de1
commit 088118cc5d
3 changed files with 19 additions and 15 deletions
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22
src/arithmetic.rs
View file

@ -432,7 +432,7 @@ fn log2_floor(num: usize) -> u32 {
}
/// Returns coefficients of an n - 1 degree polynomial given a set of n points and their evaluations
pub fn interpolate<F: Field>(points: &[F], evals: &[F]) -> Vec<F> {
pub fn lagrange_interpolate<F: Field>(points: &[F], evals: &[F]) -> Vec<F> {
assert_eq!(points.len(), evals.len());
if points.len() == 1 {
// Constant polynomial
@ -440,19 +440,23 @@ pub fn interpolate<F: Field>(points: &[F], evals: &[F]) -> Vec<F> {
} else {
let mut interpolation_polys = vec![];
for (j, x_j) in points.iter().enumerate() {
let mut tmp = vec![F::one()];
let mut tmp: Vec<F> = Vec::with_capacity(points.len() + 1);
let mut product = Vec::with_capacity(points.len() + 1);
tmp.push(F::one());
for (k, x_k) in points.iter().enumerate() {
if k != j {
// Compute (x_j - x_k)^(-1)
let denom = (*x_j - x_k).invert().unwrap();
let factor = [-denom * x_k, denom];
let mut product = vec![F::zero(); tmp.len() + factor.len() - 1];
for (i, a) in tmp.iter().enumerate() {
for (j, b) in factor.iter().enumerate() {
product[i + j] += *a * b;
}
product.resize(tmp.len() + 1, F::zero());
for (i, (a, b)) in tmp
.iter()
.chain(std::iter::once(&F::zero()))
.zip(std::iter::once(&F::zero()).chain(tmp.iter()))
.enumerate()
{
product[i] = *a * (-denom * x_k) + *b * denom;
}
tmp = product;
std::mem::swap(&mut tmp, &mut product);
}
}
interpolation_polys.push(tmp);

6
src/poly/multiopen/prover.rs
View file

@ -5,8 +5,8 @@ use super::super::{
use super::{Proof, ProverQuery};
use crate::arithmetic::{
eval_polynomial, get_challenge_scalar, interpolate, kate_division, parallelize, Challenge,
Curve, CurveAffine, Field,
eval_polynomial, get_challenge_scalar, kate_division, lagrange_interpolate, parallelize,
Challenge, Curve, CurveAffine, Field,
};
use crate::plonk::hash_point;
use crate::transcript::Hasher;
@ -91,7 +91,7 @@ impl<C: CurveAffine> Proof<C> {
.fold(None, |f_poly, ((points, evals), poly)| {
let mut poly = poly.clone()?.values;
// TODO: makes implicit asssumption that poly degree is smaller than interpolation poly degree
for (p, r) in poly.iter_mut().zip(interpolate(points, evals)) {
for (p, r) in poly.iter_mut().zip(lagrange_interpolate(points, evals)) {
*p -= &r;
}
let mut poly = points

6
src/poly/multiopen/verifier.rs
View file

@ -4,7 +4,7 @@ use super::super::{
};
use super::{Proof, VerifierQuery};
use crate::arithmetic::{
eval_polynomial, get_challenge_scalar, interpolate, Challenge, CurveAffine, Field,
eval_polynomial, get_challenge_scalar, lagrange_interpolate, Challenge, CurveAffine, Field,
};
use crate::plonk::hash_point;
use crate::transcript::Hasher;
@ -80,11 +80,11 @@ impl<'a, C: CurveAffine> Proof<C> {
C::Base::from_bytes(&(transcript_scalar.squeeze()).to_bytes()).unwrap();
transcript.absorb(transcript_scalar_point);
// Interpolate polynomial for evaluations at each set
// lagrange_Interpolate polynomial for evaluations at each set
let mut r_evals = vec![C::Scalar::zero(); point_sets.len()];
let mut r_polys: Vec<Vec<C::Scalar>> = Vec::with_capacity(point_sets.len());
for (points, evals) in point_sets.clone().iter().zip(q_eval_sets.clone().iter()) {
r_polys.push(interpolate(&points, &evals));
r_polys.push(lagrange_interpolate(&points, &evals));
}
for (r_eval, r_poly) in r_evals.iter_mut().zip(r_polys.iter()) {
*r_eval = eval_polynomial(r_poly, x_6);