commit 5767dd073ce2905f35d817f67df8a3a4d3c995dc
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jun 8 13:15:33 2015 +0100

    	PR libstdc++/66441
    	* testsuite/22_locale/conversions/string/66441.cc: New.
    	* include/bits/locale_conv.h (__do_str_codecvt): Reserve enough space
    	in the output string for BOM and complete result.

diff --git a/libstdc++-v3/include/bits/locale_conv.h b/libstdc++-v3/include/bits/locale_conv.h
index 8b0a77c..61b535c 100644
--- a/libstdc++-v3/include/bits/locale_conv.h
+++ b/libstdc++-v3/include/bits/locale_conv.h
@@ -60,12 +60,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     {
       size_t __outchars = 0;
       auto __next = __first;
-      const auto __maxlen = __cvt.max_length();
+      const auto __maxlen = __cvt.max_length() + 1;
 
       codecvt_base::result __result;
       do
 	{
-	  __outstr.resize(__outstr.size() + (__last - __next) + __maxlen);
+	  __outstr.resize(__outstr.size() + (__last - __next) * __maxlen);
 	  auto __outnext = &__outstr.front() + __outchars;
 	  auto const __outlast = &__outstr.back() + 1;
 	  __result = (__cvt.*__fn)(__state, __next, __last, __next,
diff --git a/libstdc++-v3/testsuite/22_locale/conversions/string/66441.cc b/libstdc++-v3/testsuite/22_locale/conversions/string/66441.cc
new file mode 100644
index 0000000..b72edc8
--- /dev/null
+++ b/libstdc++-v3/testsuite/22_locale/conversions/string/66441.cc
@@ -0,0 +1,49 @@
+// Copyright (C) 2015 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++11" }
+
+// libstdc++/66441
+
+#include <locale>
+#include <codecvt>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  // convert from UCS-4 to UTF16BE with BOM.
+  using cvt = std::codecvt_utf16<char32_t, 0x10FFFF, std::generate_header>;
+  std::wstring_convert<cvt, char32_t> conv;
+  auto to = conv.to_bytes(U"ab\u00e7");
+
+  VERIFY( to.length() == 8 );
+  VERIFY( (unsigned char)to[0] == 0xfe );
+  VERIFY( (unsigned char)to[1] == 0xff );
+  VERIFY( (unsigned char)to[2] == 0x00 );
+  VERIFY( (unsigned char)to[3] == 0x61 );
+  VERIFY( (unsigned char)to[4] == 0x00 );
+  VERIFY( (unsigned char)to[5] == 0x62 );
+  VERIFY( (unsigned char)to[6] == 0x00 );
+  VERIFY( (unsigned char)to[7] == 0xe7 );
+}
+
+int
+main()
+{
+  test01();
+}