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Batch inversions during domain setup.

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Sean Bowe 2020-09-06 12:44:36 -06:00
parent ff8f9eb20e
commit 3157fdd7d0
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GPG key ID: 95684257D8F8B031
1 changed files with 18 additions and 9 deletions
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27
src/plonk/domain.rs
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@ -1,4 +1,4 @@
use crate::arithmetic::{best_fft, parallelize, Field, Group}; use crate::arithmetic::{best_fft, parallelize, BatchInvert, Field, Group};
/// Describes a relative location in the evaluation domain; applying a rotation /// Describes a relative location in the evaluation domain; applying a rotation
/// by i will rotate the vector in the evaluation domain by i. /// by i will rotate the vector in the evaluation domain by i.
@ -57,24 +57,20 @@ impl<G: Group> EvaluationDomain<G> {
extended_omega = extended_omega.square(); extended_omega = extended_omega.square();
} }
let extended_omega = extended_omega; // 2^{j+k}'th root of unity let extended_omega = extended_omega; // 2^{j+k}'th root of unity
let extended_omega_inv = extended_omega.invert().unwrap(); let mut extended_omega_inv = extended_omega; // Inversion computed later
let mut omega = extended_omega; let mut omega = extended_omega;
for _ in k..extended_k { for _ in k..extended_k {
omega = omega.square(); omega = omega.square();
} }
let omega = omega; // 2^{k}'th root of unity let omega = omega; // 2^{k}'th root of unity
let omega_inv = omega.invert().unwrap(); let mut omega_inv = omega; // Inversion computed later
// We use zeta here because we know it generates a coset, and it's available // We use zeta here because we know it generates a coset, and it's available
// already. // already.
let g_coset = G::Scalar::ZETA; let g_coset = G::Scalar::ZETA;
let g_coset_inv = g_coset.square(); let g_coset_inv = g_coset.square();
// TODO: merge these inversions together with t_evaluations batch inversion?
let ifft_divisor = G::Scalar::from_u64(1 << k).invert().unwrap();
let extended_ifft_divisor = G::Scalar::from_u64(1 << extended_k).invert().unwrap();
let mut t_evaluations = Vec::with_capacity(1 << (extended_k - k)); let mut t_evaluations = Vec::with_capacity(1 << (extended_k - k));
{ {
// Compute the evaluations of t(X) in the coset evaluation domain. // Compute the evaluations of t(X) in the coset evaluation domain.
@ -97,12 +93,25 @@ impl<G: Group> EvaluationDomain<G> {
} }
// Invert, because we're dividing by this polynomial. // Invert, because we're dividing by this polynomial.
G::Scalar::batch_invert(&mut t_evaluations); // We invert in a batch, below.
} }
let mut ifft_divisor = G::Scalar::from_u64(1 << k); // Inversion computed later
let mut extended_ifft_divisor = G::Scalar::from_u64(1 << extended_k); // Inversion computed later
// The barycentric weight of 1 over the evaluation domain // The barycentric weight of 1 over the evaluation domain
// 1 / \prod_{i != 0} (1 - omega^i) // 1 / \prod_{i != 0} (1 - omega^i)
let barycentric_weight = G::Scalar::from(n).invert().unwrap(); let mut barycentric_weight = G::Scalar::from(n); // Inversion computed later
// Compute batch inversion
t_evaluations
.iter_mut()
.chain(Some(&mut ifft_divisor))
.chain(Some(&mut extended_ifft_divisor))
.chain(Some(&mut barycentric_weight))
.chain(Some(&mut extended_omega_inv))
.chain(Some(&mut omega_inv))
.batch_invert();
EvaluationDomain { EvaluationDomain {
n, n,