On Tue, 3 Jun 2025 at 13:13, Tomasz Kaminski <tkami...@redhat.com> wrote:
>
>
>
> On Fri, May 30, 2025 at 6:47 PM Luc Grosheintz <luc.groshei...@gmail.com>
> wrote:
>>
>> Implements the parts of layout_left that don't depend on any of the
>> other layouts.
>>
>> libstdc++-v3/ChangeLog:
>>
>> * include/std/mdspan (layout_left): New class.
>> * src/c++23/std.cc.in: Add layout_left.
>>
>> Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
>> ---
>> libstdc++-v3/include/std/mdspan | 306 ++++++++++++++++++++++++++++++-
>> libstdc++-v3/src/c++23/std.cc.in | 1 +
>> 2 files changed, 306 insertions(+), 1 deletion(-)
>
> LGTM. One very small formatting change, that does not need to be addressed,
> if there will not be any feedback requiring changes in next patches.
>>
>>
>> diff --git a/libstdc++-v3/include/std/mdspan
>> b/libstdc++-v3/include/std/mdspan
>> index 0f49b0e09a0..904856ebb4f 100644
>> --- a/libstdc++-v3/include/std/mdspan
>> +++ b/libstdc++-v3/include/std/mdspan
>> @@ -144,6 +144,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> { return __exts[__i]; });
>> }
>>
>> + static constexpr span<const size_t>
>> + _S_static_extents(size_t __begin, size_t __end) noexcept
>> + {
>> + return {_Extents.data() + __begin, _Extents.data() + __end};
>> + }
>> +
>> + constexpr span<const _IndexType>
>> + _M_dynamic_extents(size_t __begin, size_t __end) const noexcept
>> + requires (_Extents.size() > 0)
>> + {
>> + return {_M_dyn_exts + _S_dynamic_index[__begin],
>> + _M_dyn_exts + _S_dynamic_index[__end]};
>> + }
>> +
>> private:
>> using _S_storage = __array_traits<_IndexType,
>> _S_rank_dynamic>::_Type;
>> [[no_unique_address]] _S_storage _M_dyn_exts{};
>> @@ -160,6 +174,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> || _Extent <= numeric_limits<_IndexType>::max();
>> }
>>
>> + namespace __mdspan
>> + {
>> + template<typename _Extents>
>> + constexpr span<const size_t>
>> + __static_extents(size_t __begin = 0, size_t __end = _Extents::rank())
>> + noexcept
>> + { return _Extents::_S_storage::_S_static_extents(__begin, __end); }
>> +
>> + template<typename _Extents>
>> + constexpr span<const typename _Extents::index_type>
>> + __dynamic_extents(const _Extents& __exts, size_t __begin = 0,
>> + size_t __end = _Extents::rank()) noexcept
>> + {
>> + return __exts._M_exts._M_dynamic_extents(__begin, __end);
>> + }
>> + }
>> +
>> template<typename _IndexType, size_t... _Extents>
>> class extents
>> {
>> @@ -251,7 +282,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> : _M_exts(span<const _OIndexType, _Nm>(__exts))
>> { }
>>
>> -
>> template<__mdspan::__valid_index_type<index_type> _OIndexType, size_t
>> _Nm>
>> requires (_Nm == rank() || _Nm == rank_dynamic())
>> constexpr explicit(_Nm != rank_dynamic())
>> @@ -276,6 +306,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> }
>>
>> private:
>> + friend span<const size_t>
>> + __mdspan::__static_extents<extents>(size_t, size_t);
>> +
>> + friend span<const index_type>
>> + __mdspan::__dynamic_extents<extents>(const extents&, size_t, size_t);
>> +
>> using _S_storage = __mdspan::_ExtentsStorage<
>> _IndexType, array<size_t, sizeof...(_Extents)>{_Extents...}>;
>> [[no_unique_address]] _S_storage _M_exts;
>> @@ -286,6 +322,72 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>
>> namespace __mdspan
>> {
>> + template<typename _Tp, size_t _Nm>
>> + constexpr bool
>> + __contains_zero(span<_Tp, _Nm> __exts) noexcept
>> + {
>> + for (size_t __i = 0; __i < __exts.size(); ++__i)
>> + if (__exts[__i] == 0)
>> + return true;
>> + return false;
>> + }
>> +
>> + template<typename _Extents>
>> + constexpr bool
>> + __empty(const _Extents& __exts) noexcept
>> + {
>> + if constexpr (__contains_zero(__static_extents<_Extents>()))
>> + return true;
>> + else
>> + {
>
> I would preffer continuing if/else chain here:
> + if constexpr (__contains_zero(__static_extents<_Extents>()))
> + return true;
> + else if if constexpr (_Extents::rank_dynamic() > 0)
> + return __contains_zero(__dynamic_extents(__exts));
> + else
> + return false;
> But changing it is not necessary, so if there are no major comments for other
> patches, we do not need to create new revision.
Agreed - feel free to change that yourself and push, Tomasz.
OK for trunk either way, with or without that change.
>>
>> + if constexpr (_Extents::rank_dynamic() > 0)
>> + return __contains_zero(__dynamic_extents(__exts));
>> + else
>> + return false;
>>
>> + }
>> + }
>> +
>> + constexpr size_t
>> + __static_extents_prod(const auto& __sta_exts) noexcept
>> + {
>> + size_t __ret = 1;
>> + for (auto __factor : __sta_exts)
>> + if (__factor != dynamic_extent)
>> + __ret *= __factor;
>> + return __ret;
>> + }
>> +
>> + template<typename _Extents>
>> + constexpr typename _Extents::index_type
>> + __exts_prod(const _Extents& __exts, size_t __begin, size_t __end)
>> noexcept
>> + {
>> + using _IndexType = typename _Extents::index_type;
>> +
>> + size_t __ret = 1;
>> + if constexpr (_Extents::rank_dynamic() != _Extents::rank())
>> + {
>> + auto __sta_exts = __static_extents<_Extents>(__begin, __end);
>> + __ret = __static_extents_prod(__sta_exts);
>> + if (__ret == 0)
>> + return 0;
>> + }
>> +
>> + if constexpr (_Extents::rank_dynamic() > 0)
>> + for (auto __factor : __dynamic_extents(__exts, __begin, __end))
>> + __ret *= size_t(__factor);
>> + return _IndexType(__ret);
>> + }
>> +
>> + template<typename _Extents>
>> + constexpr typename _Extents::index_type
>> + __fwd_prod(const _Extents& __exts, size_t __r) noexcept
>> + { return __exts_prod(__exts, 0, __r); }
>> +
>> + template<typename _Extents>
>> + constexpr typename _Extents::index_type
>> + __rev_prod(const _Extents& __exts, size_t __r) noexcept
>> + { return __exts_prod(__exts, __r + 1, __exts.rank()); }
>> +
>> template<typename _IndexType, size_t... _Counts>
>> auto __build_dextents_type(integer_sequence<size_t, _Counts...>)
>> -> extents<_IndexType, ((void) _Counts, dynamic_extent)...>;
>> @@ -304,6 +406,208 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> explicit extents(_Integrals...) ->
>> extents<size_t, __mdspan::__dynamic_extent<_Integrals>()...>;
>>
>> + struct layout_left
>> + {
>> + template<typename _Extents>
>> + class mapping;
>> + };
>> +
>> + namespace __mdspan
>> + {
>> + template<typename _Tp>
>> + constexpr bool __is_extents = false;
>> +
>> + template<typename _IndexType, size_t... _Extents>
>> + constexpr bool __is_extents<extents<_IndexType, _Extents...>> = true;
>> +
>> + template<typename _Extents, typename... _Indices>
>> + constexpr typename _Extents::index_type
>> + __linear_index_left(const _Extents& __exts, _Indices... __indices)
>> + noexcept
>> + {
>> + using _IndexType = typename _Extents::index_type;
>> + _IndexType __res = 0;
>> + if constexpr (sizeof...(__indices) > 0)
>> + {
>> + _IndexType __mult = 1;
>> + auto __update = [&, __pos = 0u](_IndexType __idx) mutable
>> + {
>> + __res += __idx * __mult;
>> + __mult *= __exts.extent(__pos);
>> + ++__pos;
>> + };
>> + (__update(__indices), ...);
>> + }
>> + return __res;
>> + }
>> +
>> + template<typename _Extents,
>> + typename _IndexType = typename _Extents::index_type>
>> + consteval _IndexType
>> + __static_quotient(_IndexType __nom =
>> numeric_limits<_IndexType>::max())
>> + {
>> + auto __sta_exts = __static_extents<_Extents>();
>> + for (auto __factor : __sta_exts)
>> + {
>> + if (__factor != dynamic_extent)
>> + __nom /= _IndexType(__factor);
>> + if (__nom == 0)
>> + break;
>> + }
>> + return __nom;
>> + }
>> +
>> + template<typename _Extents>
>> + constexpr bool
>> + __is_representable_extents(const _Extents& __exts) noexcept
>> + {
>> + using _IndexType = _Extents::index_type;
>> +
>> + if constexpr (__contains_zero(__static_extents<_Extents>()))
>> + return true;
>> + else
>> + {
>> + constexpr auto __sta_quo = __static_quotient<_Extents>();
>> + if constexpr (_Extents::rank_dynamic() == 0)
>> + return __sta_quo != 0;
>> + else
>> + {
>> + auto __dyn_exts = __dynamic_extents(__exts);
>> + if (__contains_zero(__dyn_exts))
>> + return true;
>> +
>> + if constexpr (__sta_quo == 0)
>> + return false;
>> + else
>> + {
>> + auto __dyn_quo = _IndexType(__sta_quo);
>> + for (auto __factor : __dyn_exts)
>> + {
>> + __dyn_quo /= __factor;
>> + if (__dyn_quo == 0)
>> + return false;
>> + }
>> + return true;
>> + }
>> + }
>> + }
>> + }
>> +
>> + template<typename _Extents, typename _IndexType>
>> + concept __representable_size = _Extents::rank_dynamic() != 0
>> + || __contains_zero(__static_extents<_Extents>())
>> + || (__static_quotient<_Extents, _IndexType>() != 0);
>> +
>> + template<typename _Layout, typename _Mapping>
>> + concept __mapping_of =
>> + is_same_v<typename _Layout::mapping<typename _Mapping::extents_type>,
>> + _Mapping>;
>> +
>> + template<typename _Mapping>
>> + concept __standardized_mapping = __mapping_of<layout_left, _Mapping>;
>> +
>> + // A tag type to create internal ctors.
>> + class __internal_ctor
>> + { };
>> + }
>> +
>> + template<typename _Extents>
>> + class layout_left::mapping
>> + {
>> + public:
>> + using extents_type = _Extents;
>> + using index_type = typename extents_type::index_type;
>> + using size_type = typename extents_type::size_type;
>> + using rank_type = typename extents_type::rank_type;
>> + using layout_type = layout_left;
>> +
>> + static_assert(__mdspan::__representable_size<extents_type,
>> index_type>,
>> + "The size of extents_type must be representable as index_type");
>> +
>> + constexpr
>> + mapping() noexcept = default;
>> +
>> + constexpr
>> + mapping(const mapping&) noexcept = default;
>> +
>> + constexpr
>> + mapping(const extents_type& __extents) noexcept
>> + : _M_extents(__extents)
>> + { __glibcxx_assert(__mdspan::__is_representable_extents(_M_extents));
>> }
>> +
>> + template<typename _OExtents>
>> + requires is_constructible_v<extents_type, _OExtents>
>> + constexpr explicit(!is_convertible_v<_OExtents, extents_type>)
>> + mapping(const mapping<_OExtents>& __other) noexcept
>> + : mapping(__other.extents(), __mdspan::__internal_ctor{})
>> + { }
>> +
>> + constexpr mapping&
>> + operator=(const mapping&) noexcept = default;
>> +
>> + constexpr const extents_type&
>> + extents() const noexcept { return _M_extents; }
>> +
>> + constexpr index_type
>> + required_span_size() const noexcept
>> + { return __mdspan::__fwd_prod(_M_extents, extents_type::rank()); }
>> +
>> + template<__mdspan::__valid_index_type<index_type>... _Indices>
>> + requires (sizeof...(_Indices) == extents_type::rank())
>> + constexpr index_type
>> + operator()(_Indices... __indices) const noexcept
>> + {
>> + return __mdspan::__linear_index_left(_M_extents,
>> + static_cast<index_type>(__indices)...);
>> + }
>> +
>> + static constexpr bool
>> + is_always_unique() noexcept { return true; }
>> +
>> + static constexpr bool
>> + is_always_exhaustive() noexcept { return true; }
>> +
>> + static constexpr bool
>> + is_always_strided() noexcept { return true; }
>> +
>> + static constexpr bool
>> + is_unique() noexcept { return true; }
>> +
>> + static constexpr bool
>> + is_exhaustive() noexcept { return true; }
>> +
>> + static constexpr bool
>> + is_strided() noexcept { return true; }
>> +
>> + constexpr index_type
>> + stride(rank_type __i) const noexcept
>> + requires (extents_type::rank() > 0)
>> + {
>> + __glibcxx_assert(__i < extents_type::rank());
>> + return __mdspan::__fwd_prod(_M_extents, __i);
>> + }
>> +
>> + template<typename _OExtents>
>> + requires (extents_type::rank() == _OExtents::rank())
>> + friend constexpr bool
>> + operator==(const mapping& __self, const mapping<_OExtents>& __other)
>> + noexcept
>> + { return __self.extents() == __other.extents(); }
>> +
>> + private:
>> + template<typename _OExtents>
>> + constexpr explicit
>> + mapping(const _OExtents& __oexts, __mdspan::__internal_ctor) noexcept
>> + : _M_extents(__oexts)
>> + {
>> + static_assert(__mdspan::__representable_size<_OExtents,
>> index_type>,
>> + "The size of OtherExtents must be representable as index_type");
>> + __glibcxx_assert(__mdspan::__is_representable_extents(_M_extents));
>> + }
>> +
>> + [[no_unique_address]] extents_type _M_extents{};
>> + };
>> +
>> _GLIBCXX_END_NAMESPACE_VERSION
>> }
>> #endif
>> diff --git a/libstdc++-v3/src/c++23/std.cc.in
>> b/libstdc++-v3/src/c++23/std.cc.in
>> index ba468530338..8ea57132a2a 100644
>> --- a/libstdc++-v3/src/c++23/std.cc.in
>> +++ b/libstdc++-v3/src/c++23/std.cc.in
>> @@ -1844,6 +1844,7 @@ export namespace std
>> export namespace std
>> {
>> using std::extents;
>> + using std::layout_left;
>> // FIXME layout_*, default_accessor and mdspan
>> }
>> #endif
>> --
>> 2.49.0
>>
