[patch] libstdc++/66441 Fix wstring_convert when generating BOM

[patch] libstdc++/66441 Fix wstring_convert when generating BOM

[Jonathan Wakely]

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If the codecvt facet generates a BOM on every call to out() then we
need to ensure there is enough capacity in the output string for the
entire result, otherwise we loop and insert more than one BOM into the
result.

Tested powerpc64-linux and powerpc64-linux.

Committing to trunk and gcc-5-branch.

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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();
+}