re PR libstdc++/59603 (std::random_shuffle tries to swap element with itself)

	PR libstdc++/59603
	* include/bits/stl_algo.h (random_shuffle): Prevent self-swapping.
	* testsuite/25_algorithms/random_shuffle/59603.cc: New.

From-SVN: r218454

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index de13b7cebd73454ae59d575f80d5ad13fa32e48c..ac06a3a0a27f65d2accd6e8ac2ac4ecddd67e297 100644 (file)
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -15,6 +15,10 @@
        * testsuite/20_util/tuple/61947.cc: New.
        * testsuite/20_util/uses_allocator/cons_neg.cc: Adjust dg-error line.
 
+       PR libstdc++/59603
+       * include/bits/stl_algo.h (random_shuffle): Prevent self-swapping.
+       * testsuite/25_algorithms/random_shuffle/59603.cc: New.
+
 2014-11-27  Thomas Preud'homme  <thomas.preudhomme@arm.com>
 
        Backport from mainline

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 7fa7133aeee8290064de80701b0a3677391aca5f..3a33bf403824139ebe329149dd20f38ceff1c573 100644 (file)
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -5193,7 +5193,12 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
 
       if (__first != __last)
        for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
-         std::iter_swap(__i, __first + (std::rand() % ((__i - __first) + 1)));
+         {
+           _RandomAccessIterator __j = __first
+                                       + std::rand() % ((__i - __first) + 1);
+           if (__i != __j)
+             std::iter_swap(__i, __j);
+         }
     }
 
   /**
@@ -5227,7 +5232,11 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
       if (__first == __last)
        return;
       for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
-       std::iter_swap(__i, __first + __rand((__i - __first) + 1));
+       {
+         _RandomAccessIterator __j = __first + __rand((__i - __first) + 1);
+         if (__i != __j)
+           std::iter_swap(__i, __j);
+       }
     }
 
 

diff --git a/libstdc++-v3/testsuite/25_algorithms/random_shuffle/59603.cc b/libstdc++-v3/testsuite/25_algorithms/random_shuffle/59603.cc
new file mode 100644 (file)
index 0000000..7b179ac
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/random_shuffle/59603.cc
@@ -0,0 +1,34 @@
+// Copyright (C) 2014 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" }
+// { dg-require-debug-mode "" }
+
+// libstdc++/59603
+
+#include <algorithm>
+#include <vector>
+
+struct C {
+    std::vector<int> v;
+    C (int a) : v{a} {};
+};
+
+int main () {
+    std::vector<C> cs { {1}, {2}, {3}, {4} };
+    std::random_shuffle(cs.begin(), cs.end());
+}