Don't mutate the witness during permutation argument. Also, adds parallelism and reduces state/multiplications.

src/plonk.rs

@@ -116,6 +116,7 @@ fn test_proving() {
         sm: FixedWire,
 
         perm: usize,
+        perm2: usize,
     }
 
     trait StandardCS<FF: Field> {
@@ -242,7 +243,9 @@ fn test_proving() {
             };
 
             self.cs
-                .copy(self.config.perm, left_wire, left.1, right_wire, right.1)
+                .copy(self.config.perm, left_wire, left.1, right_wire, right.1)?;
+            self.cs
+                .copy(self.config.perm2, left_wire, left.1, right_wire, right.1)
         }
     }
 
@@ -258,6 +261,7 @@ fn test_proving() {
             let d = meta.advice_wire();
 
             let perm = meta.permutation(&[a, b, c]);
+            let perm2 = meta.permutation(&[a, b, c]);
 
             let sm = meta.fixed_wire();
             let sa = meta.fixed_wire();
@@ -291,6 +295,7 @@ fn test_proving() {
                 sc,
                 sm,
                 perm,
+                perm2,
             }
         }
 

src/plonk/prover.rs

@@ -78,6 +78,8 @@ impl<C: CurveAffine> Proof<C> {
         // Synthesize the circuit to obtain the witness and other information.
         circuit.synthesize(&mut witness, config)?;
 
+        let witness = witness;
+
         // Create a transcript for obtaining Fiat-Shamir challenges.
         let mut transcript = HBase::init(C::Base::one());
 
@@ -132,31 +134,26 @@ impl<C: CurveAffine> Proof<C> {
         // Iterate over each permutation
         let mut permutation_modified_advice = vec![];
         for (wires, permuted_values) in srs.meta.permutations.iter().zip(srs.permutations.iter()) {
-            // Goal is to compute the fraction
+            // Goal is to compute the products of fractions
             //
             // (p_j(\omega^i) + \delta^j \omega^i \beta + \gamma) /
             // (p_j(\omega^i) + \beta s_j(\omega^i) + \gamma)
             //
             // where p_j(X) is the jth advice wire in this permutation,
             // and i is the ith row of the wire.
-            let mut modified_advice = Vec::with_capacity(wires.len());
+            let mut modified_advice = vec![C::Scalar::one(); params.n as usize];
 
             // Iterate over each wire of the permutation
             for (&(wire, _), permuted_wire_values) in wires.iter().zip(permuted_values.iter()) {
-                // Grab the advice wire's values from the witness
+                parallelize(&mut modified_advice, |modified_advice, start| {
-                let mut tmp_advice_values = witness.advice[wire.0].clone();
+                    for ((modified_advice, advice_value), permuted_advice_value) in modified_advice
-
-                // For each row i, compute
-                // p_j(\omega^i) + \beta s_j(\omega^i) + \gamma
-                // where p_j(omega^i) = tmp[i]
-                for (tmp_advice_value, permuted_advice_value) in tmp_advice_values
                         .iter_mut()
-                    .zip(permuted_wire_values.iter())
+                        .zip(witness.advice[wire.0][start..].iter())
+                        .zip(permuted_wire_values[start..].iter())
                     {
-                    *tmp_advice_value += &(x_0 * permuted_advice_value); // p_j(\omega^i) + \beta s_j(\omega^i)
+                        *modified_advice *= &(x_0 * permuted_advice_value + &x_1 + advice_value);
-                    *tmp_advice_value += &x_1; // p_j(\omega^i) + \beta s_j(\omega^i) + \gamma
                     }
-                modified_advice.push(tmp_advice_values);
+                });
             }
 
             permutation_modified_advice.push(modified_advice);
@@ -167,7 +164,6 @@ impl<C: CurveAffine> Proof<C> {
         permutation_modified_advice
             .iter_mut()
             .flat_map(|v| v.iter_mut())
-            .flat_map(|v| v.iter_mut())
             .batch_invert();
 
         for (wires, mut modified_advice) in srs
@@ -179,30 +175,30 @@ impl<C: CurveAffine> Proof<C> {
             // Iterate over each wire again, this time finishing the computation
             // of the entire fraction by computing the numerators
             let mut deltaomega = C::Scalar::one();
-            for (&(wire, _), modified_advice) in wires.iter().zip(modified_advice.iter_mut()) {
+            for &(wire, _) in wires.iter() {
-                // For each row i, we compute
+                let omega = domain.get_omega();
-                // p_j(\omega^i) + \delta^j \omega^i \beta + \gamma
+                parallelize(&mut modified_advice, |modified_advice, start| {
-                // for the jth wire of the permutation
+                    let mut deltaomega = deltaomega * &omega.pow_vartime(&[start as u64, 0, 0, 0]);
-                for (tmp_advice_value, modified_advice) in witness.advice[wire.0]
+                    for (modified_advice, advice_value) in modified_advice
                         .iter_mut()
-                    .zip(modified_advice.iter_mut())
+                        .zip(witness.advice[wire.0][start..].iter())
                     {
-                    *tmp_advice_value += &(deltaomega * &x_0); // p_j(\omega^i) + \delta^j \omega^i \beta
+                        // Multiply by p_j(\omega^i) + \delta^j \omega^i \beta
-                    *tmp_advice_value += &x_1; // p_j(\omega^i) + \delta^j \omega^i \beta + \gamma
+                        *modified_advice *= &(deltaomega * &x_0 + &x_1 + advice_value);
-                    *modified_advice *= tmp_advice_value;
+                        deltaomega *= &omega;
-                    deltaomega *= &domain.get_omega();
                     }
+                });
                 deltaomega *= &C::Scalar::DELTA;
             }
 
-            // The modified_advice vector is a vector of vectors of fractions of
+            // The modified_advice vector is a vector of products of fractions
-            // the form
+            // of the form
             //
             // (p_j(\omega^i) + \delta^j \omega^i \beta + \gamma) /
             // (p_j(\omega^i) + \beta s_j(\omega^i) + \gamma)
             //
-            // where j is the index into modified_advice, and i is the index
+            // where i is the index into modified_advice, for the jth wire in
-            // into modified_advice[j], for the jth wire in the permutation
+            // the permutation
 
             // Compute the evaluations of the permutation product polynomial
             // over our domain, starting with z[0] = 1
@@ -210,17 +206,7 @@ impl<C: CurveAffine> Proof<C> {
             for row in 1..(params.n as usize) {
                 let mut tmp = z[row - 1];
 
-                // Iterate over each wire's modified advice, where for the jth
+                tmp *= &modified_advice[row];
-                // wire we obtain the fraction
-                //
-                // (p_j(\omega^i) + \delta^j \omega^i \beta + \gamma) /
-                // (p_j(\omega^i) + \beta s_j(\omega^i) + \gamma)
-                //
-                // where i is the row of the permutation product polynomial
-                // evaluation vector that we are currently evaluating.
-                for wire_modified_advice in modified_advice.iter() {
-                    tmp *= &wire_modified_advice[row];
-                }
                 z.push(tmp);
             }