From 169d5e26ca3612801aa64846eaecf70d4463df00 Mon Sep 17 00:00:00 2001
From: "J. Burfeind" <github@aiyionpri.me>
Date: Fri, 12 Aug 2022 22:00:55 +0200
Subject: [PATCH] Add constant `EDWARDS_D` in dalek-ff-group (#78)

---
 crypto/dalek-ff-group/src/field.rs | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/crypto/dalek-ff-group/src/field.rs b/crypto/dalek-ff-group/src/field.rs
index 7e0c12d5..a5baf5d2 100644
--- a/crypto/dalek-ff-group/src/field.rs
+++ b/crypto/dalek-ff-group/src/field.rs
@@ -16,6 +16,10 @@ const FIELD_MODULUS: U256 =
 #[derive(Clone, Copy, PartialEq, Eq, Default, Debug)]
 pub struct FieldElement(U256);
 
+pub const EDWARDS_D: FieldElement = FieldElement(U256::from_be_hex(
+  "52036cee2b6ffe738cc740797779e89800700a4d4141d8ab75eb4dca135978a3",
+));
+
 pub const SQRT_M1: FieldElement = FieldElement(U256::from_be_hex(
   "2b8324804fc1df0b2b4d00993dfbd7a72f431806ad2fe478c4ee1b274a0ea0b0",
 ));
@@ -154,6 +158,14 @@ impl FieldElement {
   }
 }
 
+#[test]
+fn test_edwards_d() {
+  let a = -FieldElement(U256::from_u32(121665));
+  let b = FieldElement(U256::from_u32(121666));
+
+  assert_eq!(EDWARDS_D, a * b.invert().unwrap());
+}
+
 #[test]
 fn test_mul() {
   assert_eq!(FieldElement(FIELD_MODULUS) * FieldElement::one(), FieldElement::zero());