From 905e7284b2511f59cb5ea1890cd5e0c3d200db41 Mon Sep 17 00:00:00 2001
From: jon-chuang <9093549+jon-chuang@users.noreply.github.com>
Date: Wed, 25 Nov 2020 16:26:32 +0800
Subject: [PATCH] Reduce density of `ThreeBitCondNegLookup`

---
 src/fields/fp/mod.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/fields/fp/mod.rs b/src/fields/fp/mod.rs
index 1b96704..a6fabcf 100644
--- a/src/fields/fp/mod.rs
+++ b/src/fields/fp/mod.rs
@@ -594,10 +594,11 @@ impl<F: PrimeField> ThreeBitCondNegLookupGadget<F> for AllocatedFp<F> {
             + b[0].lc() * (c[1] - &c[0])
             + b[1].lc() * (c[2] - &c[0])
             + (c[0], Variable::One);
+        // enforce y * (1 - 2 * b_2) == res
         b.cs().enforce_constraint(
-            y_lc.clone() + y_lc.clone(),
-            b[2].lc(),
-            y_lc - result.variable,
+            y_lc.clone(),
+            b[2].lc() * F::from(2u64).neg() + (F::one(), Variable::One),
+            lc!() + result.variable,
         )?;
 
         Ok(result)