From 0b35c603410c16893ee6e7fa2b58fb2ada9f0495 Mon Sep 17 00:00:00 2001
From: Jack Grigg <jack@z.cash>
Date: Thu, 12 Dec 2019 23:15:48 +0000
Subject: [PATCH] impl ConditionallySelectable for Field

---
 Cargo.toml                        |  1 +
 src/groth16/tests/dummy_engine.rs | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/Cargo.toml b/Cargo.toml
index f329609..b056b6c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -21,6 +21,7 @@ crossbeam = { version = "0.7", optional = true }
 pairing = { version = "0.16", path = "../pairing", optional = true }
 rand_core = "0.5"
 byteorder = "1"
+subtle = "2.2.1"
 
 [dev-dependencies]
 hex-literal = "0.2"
diff --git a/src/groth16/tests/dummy_engine.rs b/src/groth16/tests/dummy_engine.rs
index c71df0d..280552b 100644
--- a/src/groth16/tests/dummy_engine.rs
+++ b/src/groth16/tests/dummy_engine.rs
@@ -10,6 +10,7 @@ use std::cmp::Ordering;
 use std::fmt;
 use std::num::Wrapping;
 use std::ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign};
+use subtle::{Choice, ConditionallySelectable};
 
 const MODULUS_R: Wrapping<u32> = Wrapping(64513);
 
@@ -22,6 +23,16 @@ impl fmt::Display for Fr {
     }
 }
 
+impl ConditionallySelectable for Fr {
+    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
+        Fr(Wrapping(u32::conditional_select(
+            &(a.0).0,
+            &(b.0).0,
+            choice,
+        )))
+    }
+}
+
 impl Neg for Fr {
     type Output = Self;