From 8d00acace58a454c6356b20238f2c723791e94ee Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@electriccoin.co>
Date: Wed, 8 Dec 2021 03:50:07 +0000
Subject: [PATCH] `impl<F: Field> Eq for Assigned<F>`

---
 halo2_proofs/src/plonk/assigned.rs | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/halo2_proofs/src/plonk/assigned.rs b/halo2_proofs/src/plonk/assigned.rs
index 3c1795c1..67e7a560 100644
--- a/halo2_proofs/src/plonk/assigned.rs
+++ b/halo2_proofs/src/plonk/assigned.rs
@@ -41,6 +41,36 @@ impl<F: Field> From<(F, F)> for Assigned<F> {
     }
 }
 
+impl<F: Field> PartialEq for Assigned<F> {
+    fn eq(&self, other: &Self) -> bool {
+        match (self, other) {
+            // At least one side is directly zero.
+            (Self::Zero, Self::Zero) => true,
+            (Self::Zero, x) | (x, Self::Zero) => x.is_zero_vartime(),
+
+            // One side is x/0 which maps to zero.
+            (Self::Rational(_, denominator), x) | (x, Self::Rational(_, denominator))
+                if denominator.is_zero_vartime() =>
+            {
+                x.is_zero_vartime()
+            }
+
+            // Okay, we need to do some actual math...
+            (Self::Trivial(lhs), Self::Trivial(rhs)) => lhs == rhs,
+            (Self::Trivial(x), Self::Rational(numerator, denominator))
+            | (Self::Rational(numerator, denominator), Self::Trivial(x)) => {
+                &(*x * denominator) == numerator
+            }
+            (
+                Self::Rational(lhs_numerator, lhs_denominator),
+                Self::Rational(rhs_numerator, rhs_denominator),
+            ) => *lhs_numerator * rhs_denominator == *lhs_denominator * rhs_numerator,
+        }
+    }
+}
+
+impl<F: Field> Eq for Assigned<F> {}
+
 impl<F: Field> Neg for Assigned<F> {
     type Output = Assigned<F>;
     fn neg(self) -> Self::Output {