Refactor commit_inner_layers

crates/prover/src/core/fri.rs

@@ -193,7 +193,8 @@ impl<'a, B: FriOps + MerkleOps<MC::H>, MC: MerkleChannel> FriProver<'a, B, MC> {
 
     /// Builds and commits to the inner FRI layers (all layers except the first and last).
     ///
-    /// All `columns` must be provided in descending order by size.
+    /// All `columns` must be provided in descending order by size. Note there is at most one column
+    /// of each size.
     ///
     /// Returns all inner layers and the evaluation of the last layer.
     fn commit_inner_layers(
@@ -214,20 +215,26 @@ impl<'a, B: FriOps + MerkleOps<MC::H>, MC: MerkleChannel> FriProver<'a, B, MC> {
         let mut layer_evaluation = LineEvaluation::new_zero(first_inner_layer_domain);
         let mut columns = columns.iter().peekable();
         let mut layers = Vec::new();
-        let mut folding_alpha = channel.draw_felt();
+        let folding_alpha = channel.draw_felt();
+
+        // Folding the max size column.
+        B::fold_circle_into_line(
+            &mut layer_evaluation,
+            columns.next().unwrap(),
+            folding_alpha,
+            twiddles,
+        );
 
         while layer_evaluation.len() > config.last_layer_domain_size() {
-            // Check for circle polys in the first layer that should be combined in this layer.
-            while let Some(column) = columns.next_if(|c| folded_size(c) == layer_evaluation.len()) {
-                B::fold_circle_into_line(&mut layer_evaluation, column, folding_alpha, twiddles);
-            }
-
             let layer = FriInnerLayerProver::new(layer_evaluation);
             MC::mix_root(channel, layer.merkle_tree.root());
-            folding_alpha = channel.draw_felt();
-            let folded_layer_evaluation = B::fold_line(&layer.evaluation, folding_alpha, twiddles);
+            let folding_alpha = channel.draw_felt();
+            layer_evaluation = B::fold_line(&layer.evaluation, folding_alpha, twiddles);
 
-            layer_evaluation = folded_layer_evaluation;
+            // Check for circle polys in the first layer that should be combined in this layer.
+            if let Some(column) = columns.next_if(|c| folded_size(c) == layer_evaluation.len()) {
+                B::fold_circle_into_line(&mut layer_evaluation, column, folding_alpha, twiddles);
+            }
             layers.push(layer);
         }