From f574726f16887112e9165f9fd0b8832eada76c2f Mon Sep 17 00:00:00 2001
From: Carl Shapiro <cshapiro@google.com>
Date: Mon, 9 Dec 2013 17:51:30 -0800
Subject: [PATCH] runtime: check for signed zero in printfloat

Fixes #6899

R=golang-dev, r, cshapiro, iant, rsc
CC=golang-dev
https://golang.org/cl/38120043
---
 src/pkg/runtime/print.c      |  5 ++++-
 test/fixedbugs/issue6899.go  | 13 +++++++++++++
 test/fixedbugs/issue6899.out |  1 +
 3 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 test/fixedbugs/issue6899.go
 create mode 100644 test/fixedbugs/issue6899.out

diff --git a/src/pkg/runtime/print.c b/src/pkg/runtime/print.c
index 8de3ae4fa1..edb5a1c2ee 100644
--- a/src/pkg/runtime/print.c
+++ b/src/pkg/runtime/print.c
@@ -236,7 +236,10 @@ runtime·printfloat(float64 v)
 	n = 7;	// digits printed
 	e = 0;	// exp
 	s = 0;	// sign
-	if(v != 0) {
+	if(v == 0) {
+		if(1/v == runtime·neginf)
+			s = 1;
+	} else {
 		// sign
 		if(v < 0) {
 			v = -v;
diff --git a/test/fixedbugs/issue6899.go b/test/fixedbugs/issue6899.go
new file mode 100644
index 0000000000..a693bf2850
--- /dev/null
+++ b/test/fixedbugs/issue6899.go
@@ -0,0 +1,13 @@
+// cmpout
+
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "math"
+
+func main() {
+	println(math.Copysign(0, -1))
+}
diff --git a/test/fixedbugs/issue6899.out b/test/fixedbugs/issue6899.out
new file mode 100644
index 0000000000..e2375f0776
--- /dev/null
+++ b/test/fixedbugs/issue6899.out
@@ -0,0 +1 @@
+-0.000000e+000
-- 
2.48.1