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libstdc++: Fix subrange::advance and subrange::prev (LWG 3433) 

This implements the proposed resolution of LWG 3433, which fixes
subrange::advance when called with a negative argument.

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.
This commit is contained in:
Patrick Palka 2020-04-28 16:34:24 -04:00
parent 69bc881574
commit 19667c82e4
3 changed files with 119 additions and 10 deletions
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8
libstdc++-v3/ChangeLog
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@ -1,3 +1,11 @@
2020-04-28 Patrick Palka <ppalka@redhat.com>
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.
2020-04-28 Jonathan Wakely <jwakely@redhat.com>
Iain Sandoe <iain@sandoe.co.uk>

25
libstdc++-v3/include/std/ranges
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@ -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)
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3433. subrange::advance(n) has UB 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;
}
};

96
libstdc++-v3/testsuite/std/ranges/subrange/lwg3433.cc Normal file
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@ -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();
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>>();
}