From 6f65620ff2b467b8824ebd61a005501dd1138fa9 Mon Sep 17 00:00:00 2001
From: wborgeaud <williamborgeaud@gmail.com>
Date: Mon, 17 Jan 2022 06:33:23 +0100
Subject: [PATCH] Add fix for recursive verifier.

---
 plonky2/src/fri/oracle.rs             | 2 ++
 plonky2/src/fri/recursive_verifier.rs | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/plonky2/src/fri/oracle.rs b/plonky2/src/fri/oracle.rs
index 27d3e129..88b0298b 100644
--- a/plonky2/src/fri/oracle.rs
+++ b/plonky2/src/fri/oracle.rs
@@ -155,6 +155,8 @@ impl<F: RichField + Extendable<D>, C: GenericConfig<D, F = F>, const D: usize>
             final_poly += quotient;
         }
         final_poly.trim();
+        // 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/434 for details.
         final_poly.coeffs.insert(0, F::Extension::ZERO);
 
         let lde_final_poly = final_poly.lde(fri_params.config.rate_bits);
diff --git a/plonky2/src/fri/recursive_verifier.rs b/plonky2/src/fri/recursive_verifier.rs
index 526456b6..2a59d457 100644
--- a/plonky2/src/fri/recursive_verifier.rs
+++ b/plonky2/src/fri/recursive_verifier.rs
@@ -281,7 +281,7 @@ impl<F: RichField + Extendable<D>, const D: usize> CircuitBuilder<F, D> {
             sum = self.div_add_extension(numerator, denominator, sum);
         }
 
-        sum
+        self.mul_extension(sum, subgroup_x)
     }
 
     fn fri_verifier_query_round<C: GenericConfig<D, F = F>>(