This implements the proposed resolution of LWG 3433, which fixes
subrange::advance when called with a negative argument.
Tested on x86_64-pc-linux-gnu, does this look OK to commit?
libstdc++-v3/ChangeLog:
LWG 3433 subrange::advance(n) has UB when n < 0
* include/std/ranges (subrange::prev): Fix typo.
(subrange::advance): Handle a negative argument as per the proposed
resolution of LWG 3433.
* testsuite/std/ranges/subrange/lwg3433.cc: New test.
---
libstdc++-v3/include/std/ranges | 25 +++--
.../testsuite/std/ranges/subrange/lwg3433.cc | 96 +++++++++++++++++++
2 files changed, 111 insertions(+), 10 deletions(-)
create mode 100644 libstdc++-v3/testsuite/std/ranges/subrange/lwg3433.cc
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 8f91598c26e..565366a8d2f 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -353,23 +353,28 @@ namespace ranges
requires bidirectional_iterator<_It>
{
auto __tmp = *this;
- __tmp.advance(--__n);
+ __tmp.advance(-__n);
return __tmp;
}
constexpr subrange&
advance(iter_difference_t<_It> __n)
{
+ // We incorporate the proposed resolution of LWG 3433 here,
+ // avoiding undefined behavior when __n < 0.
+ if constexpr (bidirectional_iterator<_It>)
+ if (__n < 0)
+ {
+ ranges::advance(_M_begin, __n);
+ if constexpr (_S_store_size)
+ _M_size._M_size += __detail::__to_unsigned_like(-__n);
+ return *this;
+ }
+
+ __glibcxx_assert(__n >= 0);
+ auto __d = __n - ranges::advance(_M_begin, __n, _M_end);
if constexpr (_S_store_size)
- {
- auto __d = __n - ranges::advance(_M_begin, __n, _M_end);
- if (__d >= 0)
- _M_size._M_size -= __detail::__to_unsigned_like(__d);
- else
- _M_size._M_size += __detail::__to_unsigned_like(-__d);
- }
- else
- ranges::advance(_M_begin, __n, _M_end);
+ _M_size._M_size -= __detail::__to_unsigned_like(__d);
return *this;
}
};
diff --git a/libstdc++-v3/testsuite/std/ranges/subrange/lwg3433.cc
b/libstdc++-v3/testsuite/std/ranges/subrange/lwg3433.cc
new file mode 100644
index 00000000000..2b01729b40f
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/subrange/lwg3433.cc
@@ -0,0 +1,96 @@
+// Copyright (C) 2020 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++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <ranges>
+#include <testsuite_iterators.h>
+#include <testsuite_hooks.h>
+
+using __gnu_test::bidirectional_iterator_wrapper;
+using __gnu_test::forward_iterator_wrapper;
+using __gnu_test::test_range;
+using __gnu_test::test_sized_range;
+using __gnu_test::test_sized_range_sized_sent;
+
+namespace ranges = std::ranges;
+
+template<typename Container>
+void
+test01()
+{
+ int x[] = {1,2,3,4,5};
+ Container r{x};
+ ranges::subrange sr = r;
+ constexpr bool sized_range_p = ranges::sized_range<decltype(sr)>;
+ constexpr bool bidirectional_p = ranges::bidirectional_range<decltype(sr)>;
+ VERIFY( ranges::equal(sr, (int[]){1,2,3,4,5}) );
+ if constexpr (sized_range_p)
+ VERIFY( sr.size() == 5 );
+
+ sr = sr.next();
+ VERIFY( ranges::equal(sr, (int[]){2,3,4,5}) );
+ if constexpr (sized_range_p)
+ VERIFY( sr.size() == 4 );
+
+ sr = std::move(sr.next(2));
+ VERIFY( ranges::equal(sr, (int[]){4,5}) );
+ if constexpr (sized_range_p)
+ VERIFY( sr.size() == 2 );
+
+ if constexpr (bidirectional_p)
+ {
+ sr = sr.prev(2);
+ VERIFY( ranges::equal(sr, (int[]){2,3,4,5}) );
+ if constexpr (sized_range_p)
+ VERIFY( sr.size() == 4 );
+
+ sr = sr.prev(1);
+ VERIFY( ranges::equal(sr, (int[]){1,2,3,4,5}) );
+ if constexpr (sized_range_p)
+ VERIFY( sr.size() == 5 );
+ }
+ else
+ sr = r;
+
+ sr.advance(1);
+ VERIFY( ranges::equal(sr, (int[]){2,3,4,5}) );
+ if constexpr (sized_range_p)
+ VERIFY( sr.size() == 4 );
+
+ if constexpr (bidirectional_p)
+ {
+ sr.advance(-1);
+ VERIFY( ranges::equal(sr, (int[]){1,2,3,4,5}) );
+ if constexpr (sized_range_p)
+ VERIFY( sr.size() == 5 );
+ }
+}
+
+int
+main()
+{
+ test01<test_sized_range_sized_sent<int, bidirectional_iterator_wrapper>>();
+ test01<test_sized_range<int, bidirectional_iterator_wrapper>>();
+ test01<test_range<int, bidirectional_iterator_wrapper>>();
+
+ test01<test_sized_range_sized_sent<int, forward_iterator_wrapper>>();
+ test01<test_sized_range<int, forward_iterator_wrapper>>();
+ test01<test_range<int, forward_iterator_wrapper>>();
+}
--
2.26.2.266.ge870325ee8
