On 5/28/25 16:22, Tomasz Kaminski wrote:
On Mon, May 26, 2025 at 4:15 PM Luc Grosheintz <luc.groshei...@gmail.com>
wrote:
Implement the parts of layout_left that depend on layout_right; and the
parts of layout_right that don't depend on layout_stride.
libstdc++-v3/ChangeLog:
* include/std/mdspan (layout_right): New class.
* src/c++23/std.cc.in: Add layout_right.
Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
LGTM. Only some very subjective comments regarding parenthesis.
Also added some comments for possible future improvements for extents
converting constructor.
---
libstdc++-v3/include/std/mdspan | 153 ++++++++++++++++++++++++++++++-
libstdc++-v3/src/c++23/std.cc.in | 1 +
2 files changed, 153 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/std/mdspan
b/libstdc++-v3/include/std/mdspan
index d81072596b4..7daa0713716 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -397,6 +397,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
class mapping;
};
+ struct layout_right
+ {
+ template<typename _Extents>
+ class mapping;
+ };
+
namespace __mdspan
{
template<typename _Tp>
@@ -489,7 +495,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_Mapping>;
template<typename _Mapping>
- concept __standardized_mapping = __mapping_of<layout_left,
_Mapping>;
+ concept __standardized_mapping = __mapping_of<layout_left, _Mapping>
+ || __mapping_of<layout_right,
_Mapping>;
template<typename M>
concept __mapping_like = requires
@@ -539,6 +546,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: mapping(__other.extents(), __mdspan::__internal_ctor{})
{ }
+ template<typename _OExtents>
+ requires (_Extents::rank() <= 1
+ && is_constructible_v<_Extents, _OExtents>)
I got confused for a moment by parametrization here. My preference would be
to use (_Extents::rank() <= 1) && is_constructible_v<_Extents, _OExtents>?
+ constexpr explicit(!is_convertible_v<_OExtents, _Extents>)
+ mapping(const layout_right::mapping<_OExtents>& __other) noexcept
+ : mapping(__other.extents(), __mdspan::__internal_ctor{})
+ { }
+
constexpr mapping&
operator=(const mapping&) noexcept = default;
@@ -606,6 +621,142 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
[[no_unique_address]] _Extents _M_extents{};
};
+ namespace __mdspan
+ {
+ template<typename _Extents, typename... _Indices>
+ constexpr typename _Extents::index_type
+ __linear_index_right(const _Extents& __exts, _Indices... __indices)
+ {
+ using _IndexType = typename _Extents::index_type;
+ array<_IndexType, sizeof...(__indices)> __ind_arr{__indices...};
+ _IndexType __res = 0;
+ if constexpr (sizeof...(__indices) > 0)
+ {
+ _IndexType __mult = 1;
+ auto __update = [&, __pos = __exts.rank()](_IndexType) mutable
+ {
+ --__pos;
+ __res += __ind_arr[__pos] * __mult;
+ __mult *= __exts.extent(__pos);
+ };
+ (__update(__indices), ...);
+ }
+ return __res;
+ }
+ }
+
+ template<typename _Extents>
+ class layout_right::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_right;
+
+ static_assert(__mdspan::__representable_size<_Extents, 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& __extents) noexcept
+ : _M_extents(__extents)
+ {
__glibcxx_assert(__mdspan::__is_representable_extents(_M_extents)); }
+
+ template<typename _OExtents>
+ requires (is_constructible_v<extents_type, _OExtents>)
I do not think this parense are necessary? Are they?
No, it seems not. I think I got confused by the need of putting
around function calls, e.g.
requires (is_foo())
requires the extra set of parens. I think that's why I started
putting them unconditionally.
I stripped all the unneeded parens I could find.
+ constexpr explicit(!is_convertible_v<_OExtents, extents_type>)
+ mapping(const mapping<_OExtents>& __other) noexcept
+ : mapping(__other.extents(), __mdspan::__internal_ctor{})
+ { }
+
+ template<class _OExtents>
+ requires (extents_type::rank() <= 1
+ && is_constructible_v<extents_type, _OExtents>)
Same comment regarding parametrization.
+ constexpr explicit(!is_convertible_v<_OExtents, extents_type>)
+ mapping(const layout_left::mapping<_OExtents>& __other) noexcept
+ : mapping(__other.extents(), __mdspan::__internal_ctor{})
+ { }
+
+ constexpr mapping&
+ operator=(const mapping&) noexcept = default;
+
+ constexpr const _Extents&
+ 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_right(
+ _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::__rev_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)
Comment for future, this is material for commits outside this series.
The check that static_extents are representable as index type is part of
the precondition
on the _S_int_cast. For static_extent in source extent we could check that
statically in
constructor:
template<typename _OIndexType, size_t... _OExtents>
requires (_S_is_compatible_extents<_OExtents...>())
constexpr explicit(_S_ctor_explicit<_OIndexType, _OExtents...>())
extents(const extents<_OIndexType, _OExtents...>& __other) noexcept
: _M_exts(__other._M_exts)
{
static_assert(
(__mdspan::__valid_static_extent<_OExtents, _IndexType> && ...),
"Extents must either be dynamic or representable as IndexType");
}
+ {
+ 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));
+ }
+
+ public:
+ [[no_unique_address]] _Extents _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 b4b0bb24a8c..e9b5709203c 100644
--- a/libstdc++-v3/src/c++23/std.cc.in
+++ b/libstdc++-v3/src/c++23/std.cc.in
@@ -1842,6 +1842,7 @@ export namespace std
{
using std::extents;
using std::layout_left;
+ using std::layout_right;
// FIXME layout_*, default_accessor and mdspan
}
#endif
--
2.49.0
