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From: Patrick Palka <ppalka@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r12-855] libstdc++: Fix condition for memoizing reverse_view::begin() [PR100621] Date: Tue, 18 May 2021 04:35:16 +0000 (GMT) [thread overview] Message-ID: <20210518043517.2CB81383D03D@sourceware.org> (raw) https://gcc.gnu.org/g:03cf8d54e5c27cfe6b184cc96757cab30d8fa1df commit r12-855-g03cf8d54e5c27cfe6b184cc96757cab30d8fa1df Author: Patrick Palka <ppalka@redhat.com> Date: Tue May 18 00:26:25 2021 -0400 libstdc++: Fix condition for memoizing reverse_view::begin() [PR100621] A range being a random access range isn't a sufficient condition for ranges::next(iter, sent) to have constant time complexity -- it must also have a sized sentinel. This adjusts the memoization condition for reverse_view accordingly. libstdc++-v3/ChangeLog: PR libstdc++/100621 * include/std/ranges (reverse_view::_S_needs_cached_begin): Set to true if the underlying non-common random-access range doesn't have a sized sentinel. Diff: --- libstdc++-v3/include/std/ranges | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges index 36bccd6b33b..70794251ec7 100644 --- a/libstdc++-v3/include/std/ranges +++ b/libstdc++-v3/include/std/ranges @@ -3228,7 +3228,9 @@ namespace views::__adaptor { private: static constexpr bool _S_needs_cached_begin - = !common_range<_Vp> && !random_access_range<_Vp>; + = !common_range<_Vp> && !(random_access_range<_Vp> + && sized_sentinel_for<sentinel_t<_Vp>, + iterator_t<_Vp>>); [[no_unique_address]] __detail::__maybe_present_t<_S_needs_cached_begin,
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