From 7ae6271616dd630bad95bf07e47b665aa0a635a9 Mon Sep 17 00:00:00 2001
From: George Tankersley <george.tankersley@gmail.com>
Date: Sun, 25 Jun 2017 20:20:59 -0400
Subject: [PATCH] add equality for field elements

---
 internal/radix51/const.go   |  5 +++++
 internal/radix51/fe.go      |  8 ++++++++
 internal/radix51/fe_test.go | 15 +++++++++++++++
 3 files changed, 28 insertions(+)

diff --git a/internal/radix51/const.go b/internal/radix51/const.go
index 9b3f6b2..ce3f2ff 100644
--- a/internal/radix51/const.go
+++ b/internal/radix51/const.go
@@ -7,3 +7,8 @@ const (
 	// The vaule 2^51-1, used in carry propagation
 	maskLow51Bits = uint64(1)<<51 - 1
 )
+
+var (
+	FieldZero FieldElement = [5]uint64{0, 0, 0, 0, 0}
+	FieldOne  FieldElement = [5]uint64{1, 0, 0, 0, 0}
+)
diff --git a/internal/radix51/fe.go b/internal/radix51/fe.go
index 09ebc86..ff7e5e1 100644
--- a/internal/radix51/fe.go
+++ b/internal/radix51/fe.go
@@ -210,6 +210,14 @@ func FeCSwap(a, b *FieldElement, c uint64) {
 	b[4] ^= t[4]
 }
 
+func FeEqual(a, b *FieldElement) uint64 {
+	var result uint64
+	for i := 0; i < 5; i++ {
+		result |= a[i] ^ b[i]
+	}
+	return (result ^ 0)
+}
+
 func FeFromBytes(v *FieldElement, x *[32]byte) {
 	v[0] = uint64(x[0])
 	v[0] |= uint64(x[1]) << 8
diff --git a/internal/radix51/fe_test.go b/internal/radix51/fe_test.go
index 217d910..ba6f4c7 100644
--- a/internal/radix51/fe_test.go
+++ b/internal/radix51/fe_test.go
@@ -144,6 +144,21 @@ func vartimeEqual(x, y FieldElement) bool {
 	return true
 }
 
+func TestFeEqual(t *testing.T) {
+	var x FieldElement = [5]uint64{1, 1, 1, 1, 1}
+	var y FieldElement = [5]uint64{5, 4, 3, 2, 1}
+
+	eq := FeEqual(&x, &x)
+	if eq != 0 {
+		t.Errorf("wrong about equality")
+	}
+
+	eq = FeEqual(&x, &y)
+	if eq == 0 {
+		t.Errorf("wrong about inequality")
+	}
+}
+
 func TestFeInvert(t *testing.T) {
 	var x FieldElement = [5]uint64{1, 1, 1, 1, 1}
 	var one FieldElement = [5]uint64{1, 0, 0, 0, 0}