[PATCH] libstdc++: P0769R2 Add shift to <algorithm>
Stephan Bergmann
sbergman@redhat.com
Mon Mar 2 09:03:00 GMT 2020
On 21/02/2020 20:29, Patrick Palka wrote:
> 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;
^ FYI, the above line causes recent Clang 10 trunk with -std=c++20 to
fail due to a "missing" typedef
> + 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
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