From 27ebc21faff9f5287278d24a95fc23494d7d5233 Mon Sep 17 00:00:00 2001
From: wborgeaud <williamborgeaud@gmail.com>
Date: Wed, 19 Jan 2022 11:57:46 +0100
Subject: [PATCH] Add comments for LDT fix in verifier

---
 plonky2/src/fri/recursive_verifier.rs | 2 ++
 plonky2/src/fri/verifier.rs           | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/plonky2/src/fri/recursive_verifier.rs b/plonky2/src/fri/recursive_verifier.rs
index 2a59d457..63d07035 100644
--- a/plonky2/src/fri/recursive_verifier.rs
+++ b/plonky2/src/fri/recursive_verifier.rs
@@ -281,6 +281,8 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
             sum = self.div_add_extension(numerator, denominator, sum);
         }
 
+        // Multiply the final polynomial by `X`, so that `final_poly` has the maximum degree for
+        // which the LDT will pass. See github.com/mir-protocol/plonky2/pull/436 for details.
         self.mul_extension(sum, subgroup_x)
     }
 
diff --git a/plonky2/src/fri/verifier.rs b/plonky2/src/fri/verifier.rs
index 2a51f6d9..40d1ab25 100644
--- a/plonky2/src/fri/verifier.rs
+++ b/plonky2/src/fri/verifier.rs
@@ -160,6 +160,8 @@ pub(crate) fn fri_combine_initial<
         sum += numerator / denominator;
     }
 
+    // Multiply the final polynomial by `X`, so that `final_poly` has the maximum degree for
+    // which the LDT will pass. See github.com/mir-protocol/plonky2/pull/436 for details.
     sum * subgroup_x
 }