From ca5b58c2b75d48656d142bb8c686369448f33945 Mon Sep 17 00:00:00 2001
From: Isis Lovecruft <isis@torproject.org>
Date: Thu, 5 Oct 2017 01:54:26 +0000
Subject: [PATCH] Clarify doc note on degenerate cases for differential
 addition.

---
 src/montgomery.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/montgomery.rs b/src/montgomery.rs
index c42fb42..bb6a9ad 100644
--- a/src/montgomery.rs
+++ b/src/montgomery.rs
@@ -327,8 +327,8 @@ impl MontgomeryPoint {
     /// results of this method are not correct, but instead result in `(0:0)`
     /// (an invalid projective point in the Montgomery model).
     ///
-    /// The doubling case is degenerate, in that using this method to accomplish
-    /// point doubling is less efficient than using `differential_double()`.
+    /// The doubling case is degenerate, in that `P ⦵ Q ∉ {O,T}`, where `T` is
+    /// the two torsion point.
     fn differential_add(&self, that: &MontgomeryPoint,
                         difference: &MontgomeryPoint) -> MontgomeryPoint {
         // XXX Do we want these debug assertions? We would need to implement