This patch adds std::shift_left and std::shift_right. Alhough these are
STL-style algos, they are nonetheless placed 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 and ranges::swap_ranges.
This implementation of std::shift_right for non-bidirectional iterators deviates
from the reference implementation a bit. The main difference is that this
implementation is significantly simpler, and yet saves around n/2 additional
iterator increments and n/2 iter_moves at the cost of around n/2 additional
iter_swaps (where n is the shift amount).
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.
---
libstdc++-v3/include/bits/ranges_algo.h | 48 +++++++++++++
.../testsuite/25_algorithms/shift_left/1.cc | 67 +++++++++++++++++++
.../testsuite/25_algorithms/shift_right/1.cc | 67 +++++++++++++++++++
3 files changed, 182 insertions(+)
create mode 100644 libstdc++-v3/testsuite/25_algorithms/shift_left/1.cc
create mode 100644 libstdc++-v3/testsuite/25_algorithms/shift_right/1.cc
diff --git a/libstdc++-v3/include/bits/ranges_algo.h
b/libstdc++-v3/include/bits/ranges_algo.h
index 7de1072abf0..c36afc6e19b 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -3683,6 +3683,54 @@ namespace ranges
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 = __result;
+ do
+ __dest = ranges::swap_ranges(__first, __result,
+ std::move(__dest), __last).in2;
+ while (__dest != __last);
+ return __result;
+ }
+ }
+
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // concepts
diff --git a/libstdc++-v3/testsuite/25_algorithms/shift_left/1.cc
b/libstdc++-v3/testsuite/25_algorithms/shift_left/1.cc
new file mode 100644
index 00000000000..9bdb843adbc
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/shift_left/1.cc
@@ -0,0 +1,67 @@
+// 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;
+
+template<int K, template<typename> typename Wrapper>
+void
+test01()
+{
+ static_assert(K == 10 || K == 11);
+ for (int i = 0; i < 15; i++)
+ {
+ int x[K];
+ for (int t = 0; t < K; t++)
+ x[t] = t;
+ test_container<int, Wrapper> cx(x);
+ auto out = std::shift_left(cx.begin(), cx.end(), i);
+ if (i < K)
+ {
+ VERIFY( out.ptr == x+(K-i) );
+ for (int j = i; j < K-i; j++)
+ VERIFY( x[j] == i+j );
+ }
+ else
+ {
+ VERIFY( out.ptr == x );
+ for (int j = 0; j < K; j++)
+ VERIFY( x[j] == j );
+ }
+ }
+}
+
+int
+main()
+{
+ test01<10, forward_iterator_wrapper>();
+ test01<10, bidirectional_iterator_wrapper>();
+ test01<10, random_access_iterator_wrapper>();
+
+ test01<11, forward_iterator_wrapper>();
+ test01<11, bidirectional_iterator_wrapper>();
+ test01<11, random_access_iterator_wrapper>();
+}
diff --git a/libstdc++-v3/testsuite/25_algorithms/shift_right/1.cc
b/libstdc++-v3/testsuite/25_algorithms/shift_right/1.cc
new file mode 100644
index 00000000000..3ce05ed287b
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/shift_right/1.cc
@@ -0,0 +1,67 @@
+// 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;
+
+template<int K, template<typename> typename Wrapper>
+void
+test01()
+{
+ static_assert(K == 10 || K == 11);
+ for (int i = 0; i < 15; i++)
+ {
+ int x[K];
+ for (int t = 0; t < K; t++)
+ x[t] = t;
+ test_container<int, Wrapper> cx(x);
+ auto out = std::shift_right(cx.begin(), cx.end(), i);
+ if (i < K)
+ {
+ VERIFY( out.ptr == x+i );
+ for (int j = i; j < K; j++)
+ VERIFY( x[j] == j-i );
+ }
+ else
+ {
+ VERIFY( out.ptr == x+K );
+ for (int j = 0; j < K; j++)
+ VERIFY( x[j] == j );
+ }
+ }
+}
+
+int
+main()
+{
+ test01<10, forward_iterator_wrapper>();
+ test01<10, bidirectional_iterator_wrapper>();
+ test01<10, random_access_iterator_wrapper>();
+
+ test01<11, forward_iterator_wrapper>();
+ test01<11, bidirectional_iterator_wrapper>();
+ test01<11, random_access_iterator_wrapper>();
+}
--
2.25.1.291.ge68e29171c
