From 950d53c325768ada4797fd16410cf56c1a7f15b7 Mon Sep 17 00:00:00 2001
From: Ben Edgington <ben@benjaminion.xyz>
Date: Wed, 11 Aug 2021 10:06:32 +0100
Subject: [PATCH] Nashatyrev feature/add g2 add dbl (#16)

* Add g2_add_or_dbl() function

* Add unit test

Co-authored-by: Anton Nashatyrev <anton.nashatyrev@gmail.com>
---
 src/bls12_381.c | 23 +++++++++++++++++++++++
 src/bls12_381.h |  1 +
 2 files changed, 24 insertions(+)

diff --git a/src/bls12_381.c b/src/bls12_381.c
index 2b758cf..1d0d5c9 100644
--- a/src/bls12_381.c
+++ b/src/bls12_381.c
@@ -356,6 +356,19 @@ void g2_mul(g2_t *out, const g2_t *a, const fr_t *b) {
     blst_p2_mult(out, a, s.b, 8 * sizeof(blst_scalar));
 }
 
+/**
+ * Add or double G2 points.
+ *
+ * This is safe if the two points are the same.
+ *
+ * @param[out] out @p a plus @p b in the group
+ * @param[in]  a   G2 group point
+ * @param[in]  b   G2 group point
+ */
+void g2_add_or_dbl(g2_t *out, const g2_t *a, const g2_t *b) {
+    blst_p2_add_or_double(out, a, b);
+}
+
 /**
  * Subtraction of G2 group elements.
  *
@@ -608,6 +621,15 @@ void p1_sub_works(void) {
     TEST_CHECK(g1_equal(&tmp, &res));
 }
 
+void p2_add_or_dbl_works(void) {
+    g2_t expected, actual;
+
+    g2_dbl(&expected, &g2_generator);
+    g2_add_or_dbl(&actual, &g2_generator, &g2_generator);
+
+    TEST_CHECK(g2_equal(&expected, &actual));
+}
+
 void p2_mul_works(void) {
     fr_t minus1;
     g2_t res;
@@ -714,6 +736,7 @@ TEST_LIST = {
     {"fr_uint64s_roundtrip", fr_uint64s_roundtrip},
     {"p1_mul_works", p1_mul_works},
     {"p1_sub_works", p1_sub_works},
+    {"p2_add_or_dbl_works", p2_add_or_dbl_works},
     {"p2_mul_works", p2_mul_works},
     {"p2_sub_works", p2_sub_works},
     {"g1_identity_is_infinity", g1_identity_is_infinity},
diff --git a/src/bls12_381.h b/src/bls12_381.h
index 4fa076a..6952434 100644
--- a/src/bls12_381.h
+++ b/src/bls12_381.h
@@ -126,6 +126,7 @@ void g1_mul(g1_t *out, const g1_t *a, const fr_t *b);
 void g1_sub(g1_t *out, const g1_t *a, const g1_t *b);
 bool g2_equal(const g2_t *a, const g2_t *b);
 void g2_mul(g2_t *out, const g2_t *a, const fr_t *b);
+void g2_add_or_dbl(g2_t *out, const g2_t *a, const g2_t *b);
 void g2_sub(g2_t *out, const g2_t *a, const g2_t *b);
 void g2_dbl(g2_t *out, const g2_t *a);
 void g1_linear_combination(g1_t *out, const g1_t *p, const fr_t *coeffs, const uint64_t len);