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Add comments to clarify implementation of permutation argument in SRS generator.

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Sean Bowe 2020-08-31 10:18:55 -06:00
parent c427795bf5
commit a2fca8a02d
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1 changed files with 29 additions and 11 deletions
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40
src/plonk/srs.rs
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@ -84,22 +84,27 @@ impl<C: CurveAffine> SRS<C> {
let mut meta = MetaCircuit::default();
let config = ConcreteCircuit::configure(&mut meta);
let mut degree = 1;
for poly in meta.gates.iter() {
degree = std::cmp::max(degree, poly.degree());
}
for permutation in &meta.permutations {
degree = std::cmp::max(degree, permutation.len() + 1);
}
let domain = EvaluationDomain::new(degree as u32, params.k);
// Get the largest permutation argument length in terms of the number of
// advice wires involved.
let mut largest_permutation_length = 0;
for permutation in &meta.permutations {
largest_permutation_length =
std::cmp::max(permutation.len(), largest_permutation_length);
}
// The permutation argument will serve alongside the gates, so must be
// accounted for.
let mut degree = largest_permutation_length;
// Account for each gate to ensure our quotient polynomial is the
// correct degree and that our extended domain is the right size.
for poly in meta.gates.iter() {
degree = std::cmp::max(degree, poly.degree());
}
let domain = EvaluationDomain::new(degree as u32, params.k);
// Compute [omega^0, omega^1, ..., omega^{params.n - 1}]
let mut omega_powers = Vec::with_capacity(params.n as usize);
{
let mut cur = C::Scalar::one();
@ -109,6 +114,7 @@ impl<C: CurveAffine> SRS<C> {
}
}
// Compute [omega_powers * \delta^0, omega_powers * \delta^1, ..., omega_powers * \delta^m]
let mut deltaomega = Vec::with_capacity(largest_permutation_length);
{
let mut cur = C::Scalar::one();
@ -129,9 +135,12 @@ impl<C: CurveAffine> SRS<C> {
copy: vec![],
};
// Initialize the copy vector to keep track of copy constraints in all
// the permutation arguments.
for permutation in &meta.permutations {
let mut wires = vec![];
for (i, _) in permutation.iter().enumerate() {
// Computes [(i, 0), (i, 1), ..., (i, n - 1)]
wires.push((0..params.n).map(|j| (i, j as usize)).collect());
}
assembly.copy.push(wires);
@ -140,7 +149,8 @@ impl<C: CurveAffine> SRS<C> {
// Synthesize the circuit to obtain SRS
circuit.synthesize(&mut assembly, config)?;
// Compute permutation polynomials
// Compute permutation polynomials, convert to coset form and
// pre-compute commitments for the SRS.
let mut permutation_commitments = vec![];
let mut permutation_polys = vec![];
let mut permutation_cosets = vec![];
@ -149,17 +159,25 @@ impl<C: CurveAffine> SRS<C> {
let mut polys = vec![];
let mut cosets = vec![];
for (i, _) in permutation.iter().enumerate() {
// Computes the permutation polynomial based on the permutation
// description in the assembly.
let permutation_poly: Vec<_> = (0..params.n as usize)
.map(|j| {
// assembly.copy[permutation_index] is indexed by wire
// i, and then indexed by row j, obtaining the index of
// the permuted value in deltaomega.
let (permuted_i, permuted_j) = assembly.copy[permutation_index][i][j];
deltaomega[permuted_i][permuted_j]
})
.collect();
// Compute commitment to permutation polynomial
commitments.push(
params
.commit_lagrange(&permutation_poly, C::Scalar::one())
.to_affine(),
);
// Store permutation polynomial and precompute its coset evaluation
polys.push(permutation_poly.clone());
cosets.push(domain.obtain_coset(permutation_poly, Rotation::default()));
}