From 5e74d4095241655ce6bf6e5d32eeaeef353b614f Mon Sep 17 00:00:00 2001
From: Robert Griesemer <gri@golang.org>
Date: Tue, 19 Apr 2016 14:42:15 -0700
Subject: [PATCH] strconv: fix ParseFloat for special forms of zero values

Fixes #15364.

Change-Id: Id2a349896064c7c9e00e36c55162068bf18162b2
Reviewed-on: https://go-review.googlesource.com/22272
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
---
 src/strconv/atof.go      |  4 +++-
 src/strconv/atof_test.go | 24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/src/strconv/atof.go b/src/strconv/atof.go
index ce76252340f..ada85e9fed6 100644
--- a/src/strconv/atof.go
+++ b/src/strconv/atof.go
@@ -244,7 +244,9 @@ func readFloat(s string) (mantissa uint64, exp int, neg, trunc, ok bool) {
 		return
 	}
 
-	exp = dp - ndMant
+	if mantissa != 0 {
+		exp = dp - ndMant
+	}
 	ok = true
 	return
 
diff --git a/src/strconv/atof_test.go b/src/strconv/atof_test.go
index 9f70cc1fd7d..0a89c3e0bfa 100644
--- a/src/strconv/atof_test.go
+++ b/src/strconv/atof_test.go
@@ -42,6 +42,30 @@ var atoftests = []atofTest{
 	{"1e-20", "1e-20", nil},
 	{"625e-3", "0.625", nil},
 
+	// zeros
+	{"0", "0", nil},
+	{"0e0", "0", nil},
+	{"-0e0", "-0", nil},
+	{"+0e0", "0", nil},
+	{"0e-0", "0", nil},
+	{"-0e-0", "-0", nil},
+	{"+0e-0", "0", nil},
+	{"0e+0", "0", nil},
+	{"-0e+0", "-0", nil},
+	{"+0e+0", "0", nil},
+	{"0e+01234567890123456789", "0", nil},
+	{"0.00e-01234567890123456789", "0", nil},
+	{"-0e+01234567890123456789", "-0", nil},
+	{"-0.00e-01234567890123456789", "-0", nil},
+	{"0e291", "0", nil}, // issue 15364
+	{"0e292", "0", nil}, // issue 15364
+	{"0e347", "0", nil}, // issue 15364
+	{"0e348", "0", nil}, // issue 15364
+	{"-0e291", "-0", nil},
+	{"-0e292", "-0", nil},
+	{"-0e347", "-0", nil},
+	{"-0e348", "-0", nil},
+
 	// NaNs
 	{"nan", "NaN", nil},
 	{"NaN", "NaN", nil},