+2020-02-24 Patrick Palka <ppalka@redhat.com>
+
+ 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.
+
2020-02-24 Jonathan Wakely <jwakely@redhat.com>
* include/bits/stream_iterator.h (istream_iterator(default_sentinel_t)):
inline constexpr __prev_permutation_fn prev_permutation{};
} // namespace ranges
+
+ template<class ForwardIterator>
+ constexpr ForwardIterator
+ shift_left(ForwardIterator __first, ForwardIterator __last,
+ typename iterator_traits<ForwardIterator>::difference_type __n)
+ {
+ __glibcxx_assert(__n >= 0);
+ if (__n == 0)
+ return __last;
+
+ auto __mid = ranges::next(__first, __n, __last);
+ if (__mid == __last)
+ return __first;
+ return std::move(std::move(__mid), std::move(__last), std::move(__first));
+ }
+
+ template<class ForwardIterator>
+ constexpr ForwardIterator
+ shift_right(ForwardIterator __first, ForwardIterator __last,
+ typename iterator_traits<ForwardIterator>::difference_type __n)
+ {
+ __glibcxx_assert(__n >= 0);
+ if (__n == 0)
+ return __first;
+
+ using _Cat = iterator_traits<ForwardIterator>::iterator_category;
+ if constexpr (derived_from<_Cat, bidirectional_iterator_tag>)
+ {
+ auto __mid = ranges::next(__last, -__n, __first);
+ if (__mid == __first)
+ return __last;
+
+ return std::move_backward(std::move(__first), std::move(__mid),
+ std::move(__last));
+ }
+ else
+ {
+ auto __result = ranges::next(__first, __n, __last);
+ if (__result == __last)
+ return __last;
+
+ auto __dest_head = __first, __dest_tail = __result;
+ while (__dest_head != __result)
+ {
+ if (__dest_tail == __last)
+ {
+ // If we get here, then we must have
+ // 2*n >= distance(__first, __last)
+ // i.e. we are shifting out at least half of the range. In
+ // this case we can safely perform the shift with a single
+ // move.
+ std::move(std::move(__first), std::move(__dest_head),
+ std::move(__result));
+ return __result;
+ }
+ ++__dest_head;
+ ++__dest_tail;
+ }
+
+ for (;;)
+ {
+ // At the start of each iteration of this outer loop, the range
+ // [__first, __result) contains those elements that after shifting
+ // the whole range right by __n, should end up in
+ // [__dest_head, __dest_tail) in order.
+
+ // The below inner loop swaps the elements of [__first, __result)
+ // and [__dest_head, __dest_tail), while simultaneously shifting
+ // the latter range by __n.
+ auto __cursor = __first;
+ while (__cursor != __result)
+ {
+ if (__dest_tail == __last)
+ {
+ // At this point the ranges [__first, result) and
+ // [__dest_head, dest_tail) are disjoint, so we can safely
+ // move the remaining elements.
+ __dest_head = std::move(__cursor, __result,
+ std::move(__dest_head));
+ std::move(std::move(__first), std::move(__cursor),
+ std::move(__dest_head));
+ return __result;
+ }
+ std::iter_swap(__cursor, __dest_head);
+ ++__dest_head;
+ ++__dest_tail;
+ ++__cursor;
+ }
+ }
+ }
+ }
+
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // concepts
--- /dev/null
+// 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 <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using __gnu_test::test_container;
+using __gnu_test::forward_iterator_wrapper;
+using __gnu_test::bidirectional_iterator_wrapper;
+using __gnu_test::random_access_iterator_wrapper;
+
+struct X
+{
+ int a = -1;
+ bool moved_from = false;
+
+ X() = default;
+
+ X(int a)
+ : a(a)
+ { }
+
+ X(const X&) = delete;
+ X& operator=(const X&) = delete;
+
+ X(X&& other)
+ {
+ if (this != &other)
+ *this = std::move(other);
+ }
+
+ X&
+ operator=(X&& other)
+ {
+ a = other.a;
+ other.moved_from = true;
+ moved_from = false;
+ return *this;
+ }
+};
+
+template<int N, template<typename> typename Wrapper>
+void
+test01()
+{
+ for (int n = 0; n < N+5; n++)
+ {
+ X x[N];
+ for (int i = 0; i < N; i++)
+ x[i] = X{i};
+ test_container<X, Wrapper> cx(x);
+ auto out = std::shift_left(cx.begin(), cx.end(), n);
+ if (n < N)
+ {
+ VERIFY( out.ptr == x+(N-n) );
+ for (int i = 0; i < N-n; i++)
+ {
+ VERIFY( x[i].a == n+i );
+ VERIFY( !x[i].moved_from );
+ }
+ for (int i = std::max(n, N-n); i < N; i++)
+ VERIFY( x[i].moved_from );
+ }
+ else
+ {
+ VERIFY( out.ptr == x );
+ for (int i = 0; i < N; i++)
+ {
+ VERIFY( x[i].a == i );
+ VERIFY( !x[i].moved_from );
+ }
+ }
+ }
+}
+
+int
+main()
+{
+ test01<23, forward_iterator_wrapper>();
+ test01<23, bidirectional_iterator_wrapper>();
+ test01<23, random_access_iterator_wrapper>();
+
+ test01<24, forward_iterator_wrapper>();
+ test01<24, bidirectional_iterator_wrapper>();
+ test01<24, random_access_iterator_wrapper>();
+}
--- /dev/null
+// 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 <testsuite_hooks.h>
+#include <testsuite_iterators.h>
+
+using __gnu_test::test_container;
+using __gnu_test::forward_iterator_wrapper;
+using __gnu_test::bidirectional_iterator_wrapper;
+using __gnu_test::random_access_iterator_wrapper;
+
+struct X
+{
+ int a = -1;
+ bool moved_from = false;
+
+ X() = default;
+
+ X(int a)
+ : a(a)
+ { }
+
+ X(const X&) = delete;
+ X& operator=(const X&) = delete;
+
+ X(X&& other)
+ {
+ if (this != &other)
+ *this = std::move(other);
+ }
+
+ X&
+ operator=(X&& other)
+ {
+ a = other.a;
+ other.moved_from = true;
+ moved_from = false;
+ return *this;
+ }
+};
+
+template<int N, template<typename> typename Wrapper>
+void
+test01()
+{
+ for (int n = 0; n < N+5; n++)
+ {
+ X x[N];
+ for (int i = 0; i < N; i++)
+ x[i] = X(i);
+ test_container<X, Wrapper> cx(x);
+ auto out = std::shift_right(cx.begin(), cx.end(), n);
+ if (n < N)
+ {
+ VERIFY( out.ptr == x+n );
+ for (int i = n; i < N; i++)
+ VERIFY( x[i].a == i-n );
+ for (int i = 0; i < std::min(n, N-n); i++)
+ VERIFY( x[i].moved_from );
+ for (int i = std::min(n, N-n); i < std::max(n, N-n); i++)
+ VERIFY( !x[i].moved_from );
+ }
+ else
+ {
+ VERIFY( out.ptr == x+N );
+ for (int i = 0; i < N; i++)
+ {
+ VERIFY( x[i].a == i );
+ VERIFY( !x[i].moved_from );
+ }
+ }
+ }
+}
+
+int
+main()
+{
+ test01<23, forward_iterator_wrapper>();
+ test01<23, bidirectional_iterator_wrapper>();
+ test01<23, random_access_iterator_wrapper>();
+
+ test01<24, forward_iterator_wrapper>();
+ test01<24, bidirectional_iterator_wrapper>();
+ test01<24, random_access_iterator_wrapper>();
+}
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