From e02416f13ef938f1408dae30774539a9f2f57049 Mon Sep 17 00:00:00 2001
From: luffykai <kaikaikai1219@gmail.com>
Date: Tue, 29 Oct 2024 23:16:56 -0700
Subject: [PATCH] fix q max overflow bits (#722)

---
 .../primitives/src/bigint/check_carry_mod_to_zero.rs   | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/circuits/primitives/src/bigint/check_carry_mod_to_zero.rs b/circuits/primitives/src/bigint/check_carry_mod_to_zero.rs
index 41fe50a92b..a8cf2e0036 100644
--- a/circuits/primitives/src/bigint/check_carry_mod_to_zero.rs
+++ b/circuits/primitives/src/bigint/check_carry_mod_to_zero.rs
@@ -77,10 +77,12 @@ impl<AB: InteractionBuilder> SubAir<AB> for CheckCarryModToZeroSubAir {
                 is_valid,
             );
         }
-        let overflow_q = OverflowInt::<AB::Expr>::from_var_vec::<AB, AB::Var>(
-            quotient,
-            self.check_carry_to_zero.limb_bits,
-        );
+        let limb_bits = self.check_carry_to_zero.limb_bits;
+        let overflow_q = OverflowInt::<AB::Expr> {
+            limbs: quotient.iter().map(|&x| x.into()).collect(),
+            max_overflow_bits: limb_bits + 1, // q can be negative, so this is the constraint we have when range check.
+            limb_max_abs: 1 << limb_bits,
+        };
         let p_limbs = self
             .modulus_limbs
             .iter()