From 1e52d68832228a56eb6b57145da97f6f21a951d4 Mon Sep 17 00:00:00 2001
From: Matthias Goergens <matthias.goergens@gmail.com>
Date: Thu, 12 Dec 2024 10:31:28 +0800
Subject: [PATCH 1/2] Use `sum` instead of writing our own

---
 ceno_zkvm/src/uint/arithmetic.rs    | 4 +---
 mpcs/src/sum_check/classic/coeff.rs | 4 +---
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/ceno_zkvm/src/uint/arithmetic.rs b/ceno_zkvm/src/uint/arithmetic.rs
index dfe33b076..729021be9 100644
--- a/ceno_zkvm/src/uint/arithmetic.rs
+++ b/ceno_zkvm/src/uint/arithmetic.rs
@@ -274,9 +274,7 @@ impl<const M: usize, const C: usize, E: ExtensionField> UIntLimbs<M, C, E> {
                 .into_iter()
                 .unzip();
 
-        let sum_expr = is_equal_per_limb
-            .iter()
-            .fold(Expression::ZERO, |acc, flag| acc.clone() + flag.expr());
+        let sum_expr = is_equal_per_limb.iter().map(ToExpr::expr).sum();
 
         let sum_flag = WitIn::from_expr(|| "sum_flag", circuit_builder, sum_expr, false)?;
         let (is_equal, diff_inv) =
diff --git a/mpcs/src/sum_check/classic/coeff.rs b/mpcs/src/sum_check/classic/coeff.rs
index 12f46880f..36d5390a6 100644
--- a/mpcs/src/sum_check/classic/coeff.rs
+++ b/mpcs/src/sum_check/classic/coeff.rs
@@ -49,9 +49,7 @@ impl<E: ExtensionField> ClassicSumCheckRoundMessage<E> for Coefficients<E> {
     }
 
     fn sum(&self) -> E {
-        self[1..]
-            .iter()
-            .fold(self[0].double(), |acc, coeff| acc + coeff)
+        self[..].iter().sum()
     }
 
     fn evaluate(&self, _: &Self::Auxiliary, challenge: &E) -> E {

From 4c597d98a84e7e9b005b6d22cae04847bc751bcb Mon Sep 17 00:00:00 2001
From: Matthias Goergens <matthias.goergens@gmail.com>
Date: Thu, 12 Dec 2024 11:12:22 +0800
Subject: [PATCH 2/2] Fix

---
 mpcs/src/sum_check/classic/coeff.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mpcs/src/sum_check/classic/coeff.rs b/mpcs/src/sum_check/classic/coeff.rs
index 36d5390a6..10d5c1c20 100644
--- a/mpcs/src/sum_check/classic/coeff.rs
+++ b/mpcs/src/sum_check/classic/coeff.rs
@@ -49,7 +49,7 @@ impl<E: ExtensionField> ClassicSumCheckRoundMessage<E> for Coefficients<E> {
     }
 
     fn sum(&self) -> E {
-        self[..].iter().sum()
+        self[0] + self[..].iter().sum::<E>()
     }
 
     fn evaluate(&self, _: &Self::Auxiliary, challenge: &E) -> E {