On Thu, Oct 2, 2025 at 11:34 AM Luc Grosheintz <[email protected]> wrote:
> This patch series contains everything up to submdspan_extents and > implements them as described in N5014, i.e. without P3663. > > The reasons to not include P3663 are: > > - Doing both allows us to benchmark the change. > My concern is that this duplicates the amount of reviews required, and work spent on this paper. > > - Carefully implementing both, automatically leads to looking at the > problem from different angles. We can spot differences between the > two proposals. One such difference is that P3663 seems to allow > ambiguous slices, e.g. slices that convert to both full_extent and > index_type. > Yes, this was an intentional change in the paper. > > - P3663 hasn't been finalized yet, if we implement it now we'll need > to keep track of the difference. That's easier (or at least not > harder) if we have a commit containing the already applied changes > from N5014. > We hope that it will be finalized in today's telecon. > > - With a casting layer in place, the changes in the paper are quite > contained, e.g. remove cases for handling tuple, slightly refine > the range checks of slices (more can be done at compile-time). > The wording before P3663 does not allow slices to be canonicalized before calling submdspan_mapping customization point, at least for user defined-layouts. This is not an issue for the sub extents, as it is not customizable. But it will show up in the next commits. Maybe it is less of the issues as __subextents will already perform most of the required checks. > > - We could easily revert P3663 if needed. > > Luc Grosheintz (4): > libstdc++: Implement strided_slice from <mdspan>. [PR110352] > libstdc++: Implement full_extent_t. [PR110352] > libstdc++: Implement submdspan_mapping_result. [PR110352] > libstdc++: Implement submdspan_extents. [PR110352] > > libstdc++-v3/include/bits/version.def | 9 + > libstdc++-v3/include/bits/version.h | 9 + > libstdc++-v3/include/std/mdspan | 311 ++++++++++++++++++ > libstdc++-v3/src/c++23/std.cc.in | 7 +- > .../testsuite/23_containers/mdspan/int_like.h | 9 + > .../mdspan/submdspan/strided_slice.cc | 46 +++ > .../mdspan/submdspan/strided_slice_neg.cc | 19 ++ > .../mdspan/submdspan/submdspan_extents.cc | 159 +++++++++ > .../mdspan/submdspan/submdspan_extents_neg.cc | 66 ++++ > 9 files changed, 633 insertions(+), 2 deletions(-) > create mode 100644 > libstdc++-v3/testsuite/23_containers/mdspan/submdspan/strided_slice.cc > create mode 100644 > libstdc++-v3/testsuite/23_containers/mdspan/submdspan/strided_slice_neg.cc > create mode 100644 > libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents.cc > create mode 100644 > libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents_neg.cc > > -- > 2.50.1 > >
