From fc502add01dc90e8fd6ce83fba23e111fa8b374b Mon Sep 17 00:00:00 2001
From: wborgeaud <williamborgeaud@gmail.com>
Date: Fri, 4 Feb 2022 20:24:58 +0100
Subject: [PATCH] Add `quotient_degree_factor` function

---
 starky/src/prover.rs   | 4 ++--
 starky/src/stark.rs    | 7 ++++++-
 starky/src/verifier.rs | 2 +-
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/starky/src/prover.rs b/starky/src/prover.rs
index 171ea92a..335d5384 100644
--- a/starky/src/prover.rs
+++ b/starky/src/prover.rs
@@ -82,7 +82,7 @@ where
         .flat_map(|mut quotient_poly| {
             quotient_poly.trim();
             quotient_poly
-                .pad(degree * (stark.constraint_degree() - 1))
+                .pad(degree * stark.quotient_degree_factor())
                 .expect("Quotient has failed, the vanishing polynomial is not divisible by `Z_H");
             // Split quotient into degree-n chunks.
             quotient_poly.chunks(degree)
@@ -162,7 +162,7 @@ where
 {
     let degree = 1 << degree_bits;
 
-    let max_degree_bits = log2_ceil(stark.constraint_degree() - 1);
+    let max_degree_bits = log2_ceil(stark.quotient_degree_factor());
     assert!(
         max_degree_bits <= rate_bits,
         "Having constraints of degree higher than the rate is not supported yet."
diff --git a/starky/src/stark.rs b/starky/src/stark.rs
index 8f112939..4b20553e 100644
--- a/starky/src/stark.rs
+++ b/starky/src/stark.rs
@@ -65,6 +65,11 @@ pub trait Stark<F: RichField + Extendable<D>, const D: usize>: Sync {
     /// The maximum constraint degree.
     fn constraint_degree(&self) -> usize;
 
+    /// The maximum constraint degree.
+    fn quotient_degree_factor(&self) -> usize {
+        1.max(self.constraint_degree() - 1)
+    }
+
     /// Computes the FRI instance used to prove this Stark.
     // TODO: Permutation polynomials.
     fn fri_instance(
@@ -77,7 +82,7 @@ pub trait Stark<F: RichField + Extendable<D>, const D: usize>: Sync {
         let no_blinding_oracle = FriOracleInfo { blinding: false };
         let trace_info = FriPolynomialInfo::from_range(0, 0..Self::COLUMNS);
         let quotient_info =
-            FriPolynomialInfo::from_range(1, 0..(self.constraint_degree() - 1) * num_challenges);
+            FriPolynomialInfo::from_range(1, 0..self.quotient_degree_factor() * num_challenges);
         let zeta_batch = FriBatchInfo {
             point: zeta,
             polynomials: [trace_info.clone(), quotient_info].concat(),
diff --git a/starky/src/verifier.rs b/starky/src/verifier.rs
index b04ec684..bb0634f5 100644
--- a/starky/src/verifier.rs
+++ b/starky/src/verifier.rs
@@ -98,7 +98,7 @@ where
     // So to reconstruct `t(zeta)` we can compute `reduce_with_powers(chunk, zeta^n)` for each
     // `quotient_degree_factor`-sized chunk of the original evaluations.
     for (i, chunk) in quotient_polys_zeta
-        .chunks(stark.constraint_degree() - 1)
+        .chunks(stark.quotient_degree_factor())
         .enumerate()
     {
         ensure!(vanishing_polys_zeta[i] == z_h_zeta * reduce_with_powers(chunk, zeta_pow_deg));