From 03cf8d54e5c27cfe6b184cc96757cab30d8fa1df Mon Sep 17 00:00:00 2001 From: Patrick Palka Date: Tue, 18 May 2021 00:26:25 -0400 Subject: [PATCH] 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. --- 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 36bccd6..7079425 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, + iterator_t<_Vp>>); [[no_unique_address]] __detail::__maybe_present_t<_S_needs_cached_begin, -- 2.7.4