Relocate computation of the degree of the constraint system to the ConstraintSystem struct.

src/plonk/circuit.rs

@@ -753,4 +753,36 @@ impl<F: Field> ConstraintSystem<F> {
         self.num_instance_columns += 1;
         tmp
     }
+
+    /// Compute the degree of the constraint system (the maximum degree of all
+    /// constraints).
+    pub fn degree(&self) -> usize {
+        // The permutation argument will serve alongside the gates, so must be
+        // accounted for.
+        let mut degree = self
+            .permutations
+            .iter()
+            .map(|p| p.required_degree())
+            .max()
+            .unwrap_or(1);
+
+        // The lookup argument also serves alongside the gates and must be accounted
+        // for.
+        degree = std::cmp::max(
+            degree,
+            self.lookups
+                .iter()
+                .map(|l| l.required_degree())
+                .max()
+                .unwrap_or(1),
+        );
+
+        // 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 self.gates.iter() {
+            degree = std::cmp::max(degree, poly.degree());
+        }
+
+        degree
+    }
 }

src/plonk/keygen.rs

@@ -25,31 +25,7 @@ where
     let mut cs = ConstraintSystem::default();
     let config = ConcreteCircuit::configure(&mut cs);
 
-    // The permutation argument will serve alongside the gates, so must be
+    let degree = cs.degree();
-    // accounted for.
-    let mut degree = cs
-        .permutations
-        .iter()
-        .map(|p| p.required_degree())
-        .max()
-        .unwrap_or(1);
-
-    // The lookup argument also serves alongside the gates and must be accounted
-    // for.
-    degree = std::cmp::max(
-        degree,
-        cs.lookups
-            .iter()
-            .map(|l| l.required_degree())
-            .max()
-            .unwrap_or(1),
-    );
-
-    // 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 cs.gates.iter() {
-        degree = std::cmp::max(degree, poly.degree());
-    }
 
     let domain = EvaluationDomain::new(degree as u32, params.k);