From 160f4ef14c12d8b846eeac498de10a0633f6d2f4 Mon Sep 17 00:00:00 2001
From: David Benjamin <davidben@chromium.org>
Date: Mon, 20 Apr 2015 20:46:18 -0400
Subject: [PATCH] Test BN_mul for negative zero.

Change-Id: I235c59c14ec08c3338c22d080f304bdf2d7adef0
Reviewed-on: https://boringssl-review.googlesource.com/4486
Reviewed-by: Adam Langley <agl@google.com>
---
 crypto/bn/bn_test.cc | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/crypto/bn/bn_test.cc b/crypto/bn/bn_test.cc
index ab147d15..3c239d3b 100644
--- a/crypto/bn/bn_test.cc
+++ b/crypto/bn/bn_test.cc
@@ -690,6 +690,21 @@ static bool test_mul(FILE *fp) {
       return false;
     }
   }
+
+  // Test that BN_mul never gives negative zero.
+  if (!BN_set_word(a.get(), 1)) {
+    return false;
+  }
+  BN_set_negative(a.get(), 1);
+  BN_zero(b.get());
+  if (!BN_mul(c.get(), a.get(), b.get(), ctx.get())) {
+    return false;
+  }
+  if (!BN_is_zero(c.get()) || BN_is_negative(c.get())) {
+    fprintf(stderr, "Multiplication test failed!\n");
+    return false;
+  }
+
   return true;
 }