libstdc++: P0769R2 Add shift to <algorithm>
This patch adds std::shift_left and std::shift_right as per P0769R2. Alhough these are STL-style algos, this patch places them in <bits/ranges_algo.h> because they make use of some functions in the ranges namespace that are more easily reachable from <bits/ranges_algo.h> than from <bits/stl_algo.h>, namely ranges::next. In order to place these algos in <bits/stl_algo.h>, we would need to include <bits/range_access.h> from <bits/stl_algo.h> which would undesirably increase the size of <bits/stl_algo.h>. libstdc++-v3/ChangeLog: P0769R2 Add shift to <algorithm> * include/bits/ranges_algo.h (shift_left, shift_right): New. * testsuite/25_algorithms/shift_left/1.cc: New test. * testsuite/25_algorithms/shift_right/1.cc: New test.
This commit is contained in:
Patrick Palka
parent
027a3f1c38
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c5eab4ed45
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@ -1,3 +1,10 @@
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2020-02-24 Patrick Palka <ppalka@redhat.com>
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P0769R2 Add shift to <algorithm>
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* include/bits/ranges_algo.h (shift_left, shift_right): New.
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* testsuite/25_algorithms/shift_left/1.cc: New test.
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* testsuite/25_algorithms/shift_right/1.cc: New test.
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2020-02-24 Jonathan Wakely <jwakely@redhat.com>
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* include/bits/stream_iterator.h (istream_iterator(default_sentinel_t)):
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@ -3683,6 +3683,98 @@ namespace ranges
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inline constexpr __prev_permutation_fn prev_permutation{};
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} // namespace ranges
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template<class ForwardIterator>
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constexpr ForwardIterator
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shift_left(ForwardIterator __first, ForwardIterator __last,
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typename iterator_traits<ForwardIterator>::difference_type __n)
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{
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__glibcxx_assert(__n >= 0);
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if (__n == 0)
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return __last;
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auto __mid = ranges::next(__first, __n, __last);
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if (__mid == __last)
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return __first;
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return std::move(std::move(__mid), std::move(__last), std::move(__first));
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}
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template<class ForwardIterator>
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constexpr ForwardIterator
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shift_right(ForwardIterator __first, ForwardIterator __last,
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typename iterator_traits<ForwardIterator>::difference_type __n)
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{
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__glibcxx_assert(__n >= 0);
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if (__n == 0)
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return __first;
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using _Cat = iterator_traits<ForwardIterator>::iterator_category;
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if constexpr (derived_from<_Cat, bidirectional_iterator_tag>)
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{
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auto __mid = ranges::next(__last, -__n, __first);
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if (__mid == __first)
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return __last;
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return std::move_backward(std::move(__first), std::move(__mid),
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std::move(__last));
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}
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else
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{
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auto __result = ranges::next(__first, __n, __last);
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if (__result == __last)
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return __last;
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auto __dest_head = __first, __dest_tail = __result;
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while (__dest_head != __result)
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{
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if (__dest_tail == __last)
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{
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// If we get here, then we must have
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// 2*n >= distance(__first, __last)
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// i.e. we are shifting out at least half of the range. In
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// this case we can safely perform the shift with a single
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// move.
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std::move(std::move(__first), std::move(__dest_head),
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std::move(__result));
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return __result;
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}
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++__dest_head;
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++__dest_tail;
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}
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for (;;)
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{
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// At the start of each iteration of this outer loop, the range
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// [__first, __result) contains those elements that after shifting
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// the whole range right by __n, should end up in
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// [__dest_head, __dest_tail) in order.
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// The below inner loop swaps the elements of [__first, __result)
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// and [__dest_head, __dest_tail), while simultaneously shifting
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// the latter range by __n.
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auto __cursor = __first;
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while (__cursor != __result)
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{
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if (__dest_tail == __last)
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{
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// At this point the ranges [__first, result) and
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// [__dest_head, dest_tail) are disjoint, so we can safely
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// move the remaining elements.
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__dest_head = std::move(__cursor, __result,
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std::move(__dest_head));
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std::move(std::move(__first), std::move(__cursor),
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std::move(__dest_head));
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return __result;
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}
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std::iter_swap(__cursor, __dest_head);
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++__dest_head;
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++__dest_tail;
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++__cursor;
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}
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}
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}
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}
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_GLIBCXX_END_NAMESPACE_VERSION
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} // namespace std
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#endif // concepts
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@ -0,0 +1,104 @@
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// Copyright (C) 2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-options "-std=gnu++2a" }
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// { dg-do run { target c++2a } }
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#include <algorithm>
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#include <testsuite_hooks.h>
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#include <testsuite_iterators.h>
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using __gnu_test::test_container;
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using __gnu_test::forward_iterator_wrapper;
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using __gnu_test::bidirectional_iterator_wrapper;
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using __gnu_test::random_access_iterator_wrapper;
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struct X
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{
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int a = -1;
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bool moved_from = false;
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X() = default;
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X(int a)
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: a(a)
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{ }
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X(const X&) = delete;
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X& operator=(const X&) = delete;
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X(X&& other)
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{
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if (this != &other)
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*this = std::move(other);
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}
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X&
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operator=(X&& other)
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{
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a = other.a;
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other.moved_from = true;
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moved_from = false;
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return *this;
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}
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};
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template<int N, template<typename> typename Wrapper>
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void
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test01()
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{
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for (int n = 0; n < N+5; n++)
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{
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X x[N];
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for (int i = 0; i < N; i++)
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x[i] = X{i};
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test_container<X, Wrapper> cx(x);
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auto out = std::shift_left(cx.begin(), cx.end(), n);
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if (n < N)
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{
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VERIFY( out.ptr == x+(N-n) );
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for (int i = 0; i < N-n; i++)
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{
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VERIFY( x[i].a == n+i );
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VERIFY( !x[i].moved_from );
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}
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for (int i = std::max(n, N-n); i < N; i++)
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VERIFY( x[i].moved_from );
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}
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else
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{
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VERIFY( out.ptr == x );
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for (int i = 0; i < N; i++)
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{
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VERIFY( x[i].a == i );
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VERIFY( !x[i].moved_from );
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}
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}
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}
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}
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int
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main()
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{
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test01<23, forward_iterator_wrapper>();
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test01<23, bidirectional_iterator_wrapper>();
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test01<23, random_access_iterator_wrapper>();
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test01<24, forward_iterator_wrapper>();
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test01<24, bidirectional_iterator_wrapper>();
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test01<24, random_access_iterator_wrapper>();
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}
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@ -0,0 +1,103 @@
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// Copyright (C) 2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-options "-std=gnu++2a" }
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// { dg-do run { target c++2a } }
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#include <algorithm>
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#include <testsuite_hooks.h>
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#include <testsuite_iterators.h>
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using __gnu_test::test_container;
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using __gnu_test::forward_iterator_wrapper;
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using __gnu_test::bidirectional_iterator_wrapper;
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using __gnu_test::random_access_iterator_wrapper;
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struct X
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{
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int a = -1;
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bool moved_from = false;
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X() = default;
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X(int a)
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: a(a)
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{ }
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X(const X&) = delete;
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X& operator=(const X&) = delete;
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X(X&& other)
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{
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if (this != &other)
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*this = std::move(other);
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}
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X&
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operator=(X&& other)
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{
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a = other.a;
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other.moved_from = true;
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moved_from = false;
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return *this;
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}
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};
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template<int N, template<typename> typename Wrapper>
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void
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test01()
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{
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for (int n = 0; n < N+5; n++)
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{
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X x[N];
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for (int i = 0; i < N; i++)
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x[i] = X(i);
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test_container<X, Wrapper> cx(x);
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auto out = std::shift_right(cx.begin(), cx.end(), n);
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if (n < N)
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{
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VERIFY( out.ptr == x+n );
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for (int i = n; i < N; i++)
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VERIFY( x[i].a == i-n );
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for (int i = 0; i < std::min(n, N-n); i++)
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VERIFY( x[i].moved_from );
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for (int i = std::min(n, N-n); i < std::max(n, N-n); i++)
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VERIFY( !x[i].moved_from );
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}
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else
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{
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VERIFY( out.ptr == x+N );
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for (int i = 0; i < N; i++)
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{
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VERIFY( x[i].a == i );
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VERIFY( !x[i].moved_from );
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}
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}
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}
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}
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int
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main()
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{
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test01<23, forward_iterator_wrapper>();
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test01<23, bidirectional_iterator_wrapper>();
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test01<23, random_access_iterator_wrapper>();
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test01<24, forward_iterator_wrapper>();
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test01<24, bidirectional_iterator_wrapper>();
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test01<24, random_access_iterator_wrapper>();
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}
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