From a59ccc7ff7a9a37e03204fd85ae3edaada408b35 Mon Sep 17 00:00:00 2001
From: Ben Edgington <ben@benjaminion.xyz>
Date: Thu, 4 Feb 2021 14:14:25 +0000
Subject: [PATCH] Add fr_negate() method

---
 src/blst_util.c      |  8 ++++++--
 src/blst_util.h      |  3 ++-
 src/blst_util_test.c | 13 +++++++++++--
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/src/blst_util.c b/src/blst_util.c
index cea87ec..b1b6ed8 100644
--- a/src/blst_util.c
+++ b/src/blst_util.c
@@ -17,9 +17,9 @@
 #include "blst_util.h"
 #include "debug_util.h"
 
-bool fr_is_one(const blst_fr *fr_p) {
+bool fr_is_one(const blst_fr *p) {
     uint64_t a[4];
-    blst_uint64_from_fr(a, fr_p);
+    blst_uint64_from_fr(a, p);
     return a[0] == 1 && a[1] == 0 && a[2] == 0 && a[3] == 0;
 }
 
@@ -35,6 +35,10 @@ bool fr_equal(const blst_fr *aa, const blst_fr *bb) {
     return a[0] == b[0] && a[1] == b[1] && a[2] == b[2] && a[3] == b[3];
 }
 
+void fr_negate(blst_fr *out, const blst_fr *in) {
+    blst_fr_cneg(out, in, true);
+}
+
 // TODO: Is there really no better way to do this?
 void p1_mul(blst_p1 *out, const blst_p1 *a, const blst_fr *b) {
     blst_scalar s;
diff --git a/src/blst_util.h b/src/blst_util.h
index acd14f7..2720573 100644
--- a/src/blst_util.h
+++ b/src/blst_util.h
@@ -23,9 +23,10 @@ static const blst_fr one =
 // The G1 identity/infinity in affine representation
 static const blst_p1_affine identity_g1_affine = {{0,0,0,0,0,0},{0,0,0,0,0,0}};
 
-bool fr_is_one(const blst_fr *fr_p);
+bool fr_is_one(const blst_fr *p);
 void fr_from_uint64(blst_fr *a, const uint64_t n);
 bool fr_equal(const blst_fr *aa, const blst_fr *bb);
+void fr_negate(blst_fr *out, const blst_fr *in);
 void p1_mul(blst_p1 *out, const blst_p1 *a, const blst_fr *b);
 void p1_sub(blst_p1 *out, const blst_p1 *a, const blst_p1 *b);
 void linear_combination_g1(blst_p1 *out, const blst_p1 *p, const blst_fr *coeffs, const uint64_t len);
diff --git a/src/blst_util_test.c b/src/blst_util_test.c
index bf0fa02..1e7d2ed 100644
--- a/src/blst_util_test.c
+++ b/src/blst_util_test.c
@@ -18,6 +18,9 @@
 #include "debug_util.h"
 #include "blst_util.h"
 
+// This is -1 (the second root of unity)
+uint64_t m1[] = {0xffffffff00000000L, 0x53bda402fffe5bfeL, 0x3339d80809a1d805L, 0x73eda753299d7d48L};
+
 void fr_is_one_works(void) {
     TEST_CHECK(true == fr_is_one(&one));
 }
@@ -39,9 +42,14 @@ void fr_equal_works(void) {
     TEST_CHECK(false == fr_equal(&a, &b));
 }
 
+void fr_negate_works(void) {
+    blst_fr minus1, res;
+    blst_fr_from_uint64(&minus1, m1);
+    fr_negate(&res, &minus1);
+    TEST_CHECK(fr_is_one(&res));
+}
+
 void p1_mul_works(void) {
-    // This is -1 (the second root of unity)
-    uint64_t m1[] = {0xffffffff00000000L, 0x53bda402fffe5bfeL, 0x3339d80809a1d805L, 0x73eda753299d7d48L};
     blst_fr minus1;
     blst_p1 g1_gen, g1_gen_neg, res;
 
@@ -100,6 +108,7 @@ TEST_LIST =
      {"fr_is_one_works", fr_is_one_works },
      {"fr_from_uint64_works", fr_from_uint64_works},
      {"fr_equal_works", fr_equal_works},
+     {"fr_negate_works", fr_negate_works},
      {"p1_mul_works", p1_mul_works},
      {"p1_sub_works", p1_sub_works},
      {"identity_g1_is_infinity", identity_g1_is_infinity},