re PR libstdc++/41351 (std::rotate on RAI does not conform to ISO complexity requirement)

2009-11-03  David Krauss  <potswa@mac.com>
	    Paolo Carlini  <paolo.carlini@oracle.com>

	PR libstdc++/41351
	* include/bits/stl_algo.h (__rotate(_RandomAccessIterator,
	_RandomAccessIterator, _RandomAccessIterator,
	random_access_iterator_tag)): Rewrite to use only std::swap in
	general and std::copy/std::copy_backward when safe.

Co-Authored-By: Paolo Carlini <paolo.carlini@oracle.com>
From-SVN: r153860

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 589671b..494e24e 100644 (file)
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,12 @@
+2009-11-03  David Krauss  <potswa@mac.com>
+           Paolo Carlini  <paolo.carlini@oracle.com>
+
+       PR libstdc++/41351
+       * include/bits/stl_algo.h (__rotate(_RandomAccessIterator,
+       _RandomAccessIterator, _RandomAccessIterator,
+       random_access_iterator_tag)): Rewrite to use only std::swap in
+       general and std::copy/std::copy_backward when safe.
+
 2009-11-02  Benjamin Kosnik  <bkoz@redhat.com>
 
        * include/std/future: Use base class with nested types.

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 70cde1a..9b6f2af 100644 (file)
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -1647,53 +1647,64 @@ _GLIBCXX_BEGIN_NAMESPACE(std)
       typedef typename iterator_traits<_RandomAccessIterator>::value_type
        _ValueType;
 
-      const _Distance __n = __last   - __first;
-      const _Distance __k = __middle - __first;
-      const _Distance __l = __n - __k;
+      _Distance __n = __last   - __first;
+      _Distance __k = __middle - __first;
 
-      if (__k == __l)
+      if (__k == __n - __k)
        {
          std::swap_ranges(__first, __middle, __middle);
          return;
        }
 
-      const _Distance __d = std::__gcd(__n, __k);
+      _RandomAccessIterator __p = __first;
 
-      for (_Distance __i = 0; __i < __d; __i++)
+      for (;;)
        {
-         _ValueType __tmp = _GLIBCXX_MOVE(*__first);
-         _RandomAccessIterator __p = __first;
-
-         if (__k < __l)
+         if (__k < __n - __k)
            {
-             for (_Distance __j = 0; __j < __l / __d; __j++)
+             if (__is_pod(_ValueType) && __k == 1)
+               {
+                 _ValueType __t = _GLIBCXX_MOVE(*__p);
+                 _GLIBCXX_MOVE3(__p + 1, __p + __n, __p);
+                 *(__p + __n - 1) = _GLIBCXX_MOVE(__t);
+                 return;
+               }
+             _RandomAccessIterator __q = __p + __k;
+             for (_Distance __i = 0; __i < __n - __k; ++ __i)
                {
-                 if (__p > __first + __l)
-                   {
-                     *__p = _GLIBCXX_MOVE(*(__p - __l));
-                     __p -= __l;
-                   }
-
-                 *__p = _GLIBCXX_MOVE(*(__p + __k));
-                 __p += __k;
+                 std::iter_swap(__p, __q);
+                 ++__p;
+                 ++__q;
                }
+             __n %= __k;
+             if (__n == 0)
+               return;
+             std::swap(__n, __k);
+             __k = __n - __k;
            }
          else
            {
-             for (_Distance __j = 0; __j < __k / __d - 1; __j ++)
+             __k = __n - __k;
+             if (__is_pod(_ValueType) && __k == 1)
                {
-                 if (__p < __last - __k)
-                   {
-                     *__p = _GLIBCXX_MOVE(*(__p + __k));
-                     __p += __k;
-                   }
-                 *__p = _GLIBCXX_MOVE(*(__p - __l));
-                 __p -= __l;
+                 _ValueType __t = _GLIBCXX_MOVE(*(__p + __n - 1));
+                 _GLIBCXX_MOVE_BACKWARD3(__p, __p + __n - 1, __p + __n);
+                 *__p = _GLIBCXX_MOVE(__t);
+                 return;
                }
+             _RandomAccessIterator __q = __p + __n;
+             __p = __q - __k;
+             for (_Distance __i = 0; __i < __n - __k; ++ __i)
+               {
+                 --__p;
+                 --__q;
+                 std::iter_swap(__p, __q);
+               }
+             __n %= __k;
+             if (__n == 0)
+               return;
+             std::swap(__n, __k);
            }
-
-         *__p = _GLIBCXX_MOVE(__tmp);
-         ++__first;
        }
     }