[gouarin]

Checklist

• The title and commit message(s) are descriptive.
• Small commits made to fix your PR have been squashed to avoid history pollution.
• Tests have been added for new features or bug fixes.
• API of new functions and classes are documented (no public API changes).

Description

xview_stepper, the stepper of views that are not strided (keep or drop slices), gave wrong results or read out of bounds in three cases:

xt::xarray<int> a = {{0, 1, 2, 3}, {4, 5, 6, 7}, {8, 9, 10, 11}};
xt::xarray<int> z = xt::zeros<int>({2, 2, 2});
xt::xarray<int> r = z + xt::view(a, xt::keep(0, 2), xt::keep(1, 3));  // {{1, 1}, {3, 3}} instead of {{1, 3}, {9, 11}}
auto v = xt::view(a, 1, xt::keep(0, 2, 3));
std::vector<int> rev(v.rbegin(), v.rend());                          // crashes
auto w = xt::view(a, xt::keep(0, 2), 1);
std::vector<int> rev2(w.rbegin(), w.rend());                         // crashes

• step and reset ignored m_offset, so a view broadcast to a higher rank moved along the wrong axes.
• m_index_keeper was indexed by slice in the constructor and to_end, but by view dimension in step and reset.
• to_end left the stepper one past the last element along the last axis of the underlying expression. That is not the innermost axis of the view when the last slice is integral or a newaxis, or when some axes have no slice.

The stepper now handles m_offset like xstepper, indexes m_index_keeper by slice, and builds the end position from the begin position. The reverse column-major check in test_view_iter, commented out because it failed for keep slices, is enabled again.

xview.keep_slice_reverse_iteration and xview.keep_broadcast_higher_rank fail on master and pass with the fix, also under AddressSanitizer and UBSan. The GCC 13/15 -Warray-bounds warnings in common_step_forward and common_reset go away too.

[codspeed]

Merging this PR will not alter performance

1 warning

⚠️ Unable to measure the execution of 1 benchmark

This benchmark measured no execution time, so its result is not comparable and counts as unchanged. This usually happens when the compiler removes the code under test.

Prevent compiler optimizations

See affected benchmarks

✅ 255 untouched benchmarks

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_{Comparing gouarin:fix-xview-stepper (e78a19f) with master (57f3d07)}