re PR libstdc++/50119 ([C++0x] copy_n advances InputIterator one more time than necessary)

2011-08-18  Paolo Carlini  <paolo.carlini@oracle.com>

	PR libstdc++/50119
	* include/bits/stl_algo.h (__copy_n(_InputIterator, _Size,
	_OutputIterator, input_iterator_tag)): Fix.
	* testsuite/25_algorithms/copy_n/50119.cc: New.

From-SVN: r177871

libstdc++-v3/ChangeLog

+2011-08-18  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR libstdc++/50119
+	* include/bits/stl_algo.h (__copy_n(_InputIterator, _Size,
+	_OutputIterator, input_iterator_tag)): Fix.
+	* testsuite/25_algorithms/copy_n/50119.cc: New.
+
 2011-08-18  Marc Glisse  <marc.glisse@normalesup.org>
 	    Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
-	PR libstdc++-v3/1773
+	PR libstdc++/1773
 	* config/os/solaris2.7: Rename to config/os/solaris2.9.
 	* config/os/solaris/solaris2.9/os_defines.h
 	(__CORRECT_ISO_CPP_MATH_H_PROTO1)

libstdc++-v3/include/bits/stl_algo.h

@@ -979,11 +979,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     __copy_n(_InputIterator __first, _Size __n,
 	     _OutputIterator __result, input_iterator_tag)
     {
-      for (; __n > 0; --__n)
+      if (__n > 0)
 	{
-	  *__result = *__first;
-	  ++__first;
-	  ++__result;
+	  while (true)
+	    {
+	      *__result = *__first;
+	      ++__result;
+	      if (--__n > 0)
+		++__first;
+	      else
+		break;
+	    }
 	}
       return __result;
     }

libstdc++-v3/testsuite/25_algorithms/copy_n/50119.cc

+// { dg-options "-std=gnu++0x" }
+
+// Copyright (C) 2011 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 Pred 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/>.
+
+#include <algorithm>
+#include <vector>
+#include <sstream>
+#include <iterator>
+#include <testsuite_hooks.h>
+
+// libstdc++/50119
+void test01()
+{
+  using namespace std;
+  bool test __attribute__((unused)) = true;
+
+  vector<int> v;
+  istringstream s("1 2 3 4 5");
+
+  copy_n(istream_iterator<int>(s), 2, back_inserter(v));
+  VERIFY( v.size() == 2 );
+  VERIFY( v[0] == 1 );
+  VERIFY( v[1] == 2 );
+
+  copy_n(istream_iterator<int>(s), 2, back_inserter(v));
+  VERIFY( v.size() == 4 );
+  VERIFY( v[0] == 1 );
+  VERIFY( v[1] == 2 );
+  VERIFY( v[2] == 3 );
+  VERIFY( v[3] == 4 );
+}
+
+int main()
+{
+  test01();
+  return 0;
+}