On 4/9/25 9:23 AM, Luc Grosheintz wrote:
This implements std::extents from <mdspan> according to N4950 and
contains partial progress towards PR107761.
If an extent changes its type, there's a precondition in the standard,
that the value is representable in the target integer type. This commit
uses a static_cast for all of these conversions, without any additional
checks.
The precondition for 'extents::{static_,}extent' is that '__r < rank()'.
For extents<T> this precondition is always violated and results in
calling __builtin_trap. For all other specializations it's checked via
__glibcxx_assert.
PR libstdc++/107761
libstdc++-v3/ChangeLog:
* include/std/mdspan (extents): New class.
* src/c++23/std.cc.in: Add 'using std::extents'.
Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
---
libstdc++-v3/include/std/mdspan | 400 +++++++++++++++++++++++++++++++
libstdc++-v3/src/c++23/std.cc.in | 6 +-
2 files changed, 405 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 4094a416d1e..5c6a1868d62 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -33,6 +33,10 @@
#pragma GCC system_header
#endif
+#include <span>
+#include <array>
+#include <type_traits>
+
#define __glibcxx_want_mdspan
#include <bits/version.h>
@@ -42,6 +46,402 @@ namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
+ namespace __detail
+ {
+ // Computed as: sum_i (i == __r) * E_i
+ template<size_t _Count, size_t... _Extents>
+ struct _StaticExtent;
+
+ template<size_t _Count, size_t _Extent, size_t... _Extents>
+ struct _StaticExtent<_Count, _Extent, _Extents...>
+ {
+ static constexpr size_t
+ _M_value(size_t __r) noexcept
+ {
+ return (_Count == __r) * _Extent
+ + _StaticExtent<_Count + 1, _Extents...>::_M_value(__r);
+ }
+ };
+
+ template<size_t _Count>
+ struct _StaticExtent<_Count>
+ {
+ static constexpr size_t
+ _M_value(size_t __r) noexcept
+ { return 0; }
+ };
+
+ // Computed as: sum_i (i < __r) * (E_i == dynamic_extent)
+ template<size_t _Count, size_t... _Extents>
+ struct _DynamicIndex;
+
+ template<size_t _Count, size_t _Extent, size_t... _Extents>
+ struct _DynamicIndex<_Count, _Extent, _Extents...>
+ {
+ static constexpr size_t
+ _M_value(size_t __r) noexcept
+ {
+ return (_Count < __r) * (_Extent == dynamic_extent)
+ + _DynamicIndex<_Count + 1, _Extents...>::_M_value(__r);
+ }
+ };
+
+ template<size_t _Count>
+ struct _DynamicIndex<_Count>
+ {
+ static constexpr size_t
+ _M_value(size_t __r) noexcept
+ { return 0; }
+ };
+
+ // Computed by: counting the number of dynamic extents (_Dr); and returning
+ // the static index first time `__di == _Dr`.
+ template<size_t _Si, size_t _Dr, size_t... _Extents>
+ struct _DynamicIndexInv;
+
+ template<size_t _Si, size_t _Dr, size_t _Extent, size_t... _Extents>
+ struct _DynamicIndexInv<_Si, _Dr, _Extent, _Extents...>
+ {
+ static constexpr size_t
+ _M_value(size_t __di) noexcept
+ {
+ if (_Extent == dynamic_extent && __di == _Dr)
+ return _Si;
+ else
+ return _DynamicIndexInv<_Si+1, _Dr + (_Extent == dynamic_extent),
+ _Extents...>
+ ::_M_value(__di);
+ }
+ };
+
+ template<size_t _Si, size_t _Dr, size_t _Extent>
+ struct _DynamicIndexInv<_Si, _Dr, _Extent>
+ {
+ static constexpr size_t
+ _M_value(size_t __di) noexcept
+ {
+ __glibcxx_assert(__di == _Dr);
+ return _Si;
+ }
+ };
+
+ // Aim: __ext[i] for template parameter packs.
+ template<size_t _Count, typename... _IndexTypes>
+ struct _GetPackElement;
+
+ template<size_t _Count, typename _IndexType, typename... _IndexTypes>
+ struct _GetPackElement<_Count, _IndexType, _IndexTypes...>
+ {
+ template<size_t _Index>
+ static constexpr const auto&
+ get(const _IndexType& __current, const _IndexTypes&... __rest)
+ {
+ if constexpr (_Index == _Count)
+ return __current;
+ else
+ return _GetPackElement<_Count+1, _IndexTypes...>
+ ::template get<_Index>(__rest...);
+ }
+ };
+
+ template<size_t _Di, typename... _IndexTypes>
+ constexpr const auto&
+ __get_element(const _IndexTypes&... __exts)
+ {
+ return _GetPackElement<0, _IndexTypes...>
+ ::template get<_Di>(__exts...);
+ }
+
+ template<size_t... _Extents>
+ struct _DynamicRank
+ {
+ static constexpr size_t _S_value = ((_Extents == dynamic_extent) + ...);
+ };
+
+ template<>
+ struct _DynamicRank<>
+ {
+ static constexpr size_t _S_value = 0;
+ };
+
+ template<typename _IndexType, typename _DynamicIndexes, typename _Indexes,
+ size_t... _Extents>
+ struct _ExtentsStorage;
+
+ template<typename _IndexType, size_t... _DynamicIndexes, size_t...
_Indexes,
+ size_t... _Extents>
+ struct _ExtentsStorage<_IndexType, index_sequence<_DynamicIndexes...>,
+ index_sequence<_Indexes...>, _Extents...>
+ {
+ static constexpr size_t _S_rank = sizeof...(_Extents);
+
+ static constexpr size_t _S_rank_dynamic =
+ _DynamicRank<_Extents...>::_S_value;
+
+ static constexpr array<size_t, _S_rank_dynamic> _S_dynamic_index_inv{
+ _DynamicIndexInv<0, 0, _Extents...> ::_M_value(_DynamicIndexes)...};
+
+ static constexpr array<size_t, _S_rank> _S_dynamic_index {
+ _DynamicIndex<0, _Extents...>::_M_value(_Indexes)...};
+
+ template<typename _Tp>
+ static constexpr _IndexType
+ _M_int_cast(const _Tp& __other)
+ { return __other; }
+
+ constexpr _ExtentsStorage() = default;
+
+ template<typename _OIndexType, typename _ODynamicIndexes,
+ typename _OIndexes, size_t... _OExtents>
+ constexpr _ExtentsStorage(
+ const _ExtentsStorage<_OIndexType, _ODynamicIndexes, _OIndexes,
+ _OExtents...>& __other)
+ : _M_dynamic_extents{_M_int_cast(__other._M_extent(
+ _S_dynamic_index_inv[_DynamicIndexes]))...}
+ { }
+
+ template<size_t _Di, typename... _OIndexTypes>
+ static constexpr const auto&
+ _M_get_dynamic_element(const _OIndexTypes&... __exts)
+ { return __get_element<_S_dynamic_index_inv[_Di]>(__exts...); }
+
+ template<typename... _OIndexTypes>
+ requires (sizeof...(_OIndexTypes) == _S_rank_dynamic)
+ && (is_convertible_v<_OIndexTypes, _IndexType> && ...)
+ constexpr
+ _ExtentsStorage(const _OIndexTypes&... __exts)
+ : _M_dynamic_extents{_M_int_cast(
+ __get_element<_DynamicIndexes>(__exts...))...}
+ { }
+
+ template<typename... _OIndexTypes>
+ requires (sizeof...(_OIndexTypes) != _S_rank_dynamic)
+ && (is_convertible_v<_OIndexTypes, _IndexType> && ...)
+ constexpr
+ _ExtentsStorage(const _OIndexTypes&... __exts)
+ : _M_dynamic_extents{_M_int_cast(
+ _M_get_dynamic_element<_DynamicIndexes>(__exts...))...}
+ { }
+
+ template<typename _OIndexType, size_t _Nm>
+ requires (_Nm == _S_rank_dynamic)
+ constexpr
+ _ExtentsStorage(const span<_OIndexType, _Nm>& __exts)
+ : _M_dynamic_extents{_M_int_cast(
+ as_const(__exts[_DynamicIndexes]))...}
+ { }
+
+ template<typename _OIndexType, size_t _Nm>
+ requires (_Nm != _S_rank_dynamic)
+ constexpr _ExtentsStorage(const span<_OIndexType, _Nm>& __exts)
+ : _M_dynamic_extents{_M_int_cast(
+ as_const(__exts[_S_dynamic_index_inv[_DynamicIndexes]]))...}
+ { }
+
+ template<typename _OIndexType, size_t _Nm>
+ requires (_Nm == _S_rank_dynamic)
+ constexpr
+ _ExtentsStorage(const array<_OIndexType, _Nm>& __exts)
+ : _M_dynamic_extents{_M_int_cast(
+ as_const(__exts[_DynamicIndexes]))...}
+ { }
+
+ template<typename _OIndexType, size_t _Nm>
+ requires (_Nm != _S_rank_dynamic)
+ constexpr _ExtentsStorage(const array<_OIndexType, _Nm>& __exts)
+ : _M_dynamic_extents{_M_int_cast(
+ as_const(__exts[_S_dynamic_index_inv[_DynamicIndexes]]))...}
+ { }
+
+ static constexpr size_t
+ _M_static_extent(size_t __r) noexcept
+ { return _StaticExtent<0, _Extents...>::_M_value(__r); }
+
+ constexpr _IndexType
+ _M_extent(size_t __r) const noexcept
+ {
+ auto __se = _M_static_extent(__r);
+ if (__se == dynamic_extent)
+ return _M_dynamic_extents[_S_dynamic_index[__r]];
+ else
+ return __se;
+ }
+ private:
+ [[no_unique_address]]
+ array<_IndexType, _S_rank_dynamic> _M_dynamic_extents;
+ };
+
+ template<typename _IndexType, size_t... _Extents>
+ using __extents_storage = _ExtentsStorage<
+ _IndexType, make_index_sequence<_DynamicRank<_Extents...>::_S_value>,
+ make_index_sequence<sizeof...(_Extents)>, _Extents...>;
+ }
+
+ template<typename _IndexType, size_t... _Extents>
+ class extents;
+
+ template<typename _SIndexType, size_t... _SExtents, typename _OIndexType,
+ size_t... _OExtents>
+ constexpr bool
+ operator==(const extents<_SIndexType, _SExtents...>& __self,
+ const extents<_OIndexType, _OExtents...>& __other) noexcept;
+
+ template<typename _IndexType, size_t... _Extents>
+ class extents
+ {
+ static_assert(is_integral_v<_IndexType>, "_IndexType must be integral.");
+
+ public:
+ using index_type = _IndexType;
+ using size_type = make_signed_t<index_type>;
This should be `make_unsigned_t` and will be fixed with the next
version of this patch series.> + using rank_type = size_t;
+
+ static constexpr rank_type
+ rank() noexcept { return _ExtentsStorage::_S_rank; }
+
+ static constexpr rank_type
+ rank_dynamic() noexcept { return _ExtentsStorage::_S_rank_dynamic; }
+
+ static constexpr size_t
+ static_extent(rank_type __r) noexcept
+ {
+ if constexpr (rank() == 0)
+ __builtin_trap();
+
+ __glibcxx_assert(__r < rank());
+ return _ExtentsStorage::_M_static_extent(__r);
+ }
+
+ constexpr index_type
+ extent(rank_type __r) const noexcept
+ {
+ if constexpr (rank() == 0)
+ __builtin_trap();
+
+ __glibcxx_assert(__r < rank());
+ return _M_extents._M_extent(__r);
+ }
+
+ constexpr
+ extents() noexcept = default;
+
+ private:
+ static constexpr bool
+ _M_is_less_dynamic(size_t __ext, size_t __oext)
+ { return (__ext != dynamic_extent) && (__oext == dynamic_extent); }
+
+ template<typename _Tp>
+ static constexpr size_t
+ _M_limits_max() { return numeric_limits<_Tp>::max(); }
+
+ template<typename _OIndexType, size_t... _OExtents>
+ static constexpr bool
+ _M_ctor_explicit()
+ {
+ return (_M_is_less_dynamic(_Extents, _OExtents) || ...)
+ || (_M_limits_max<index_type>() < _M_limits_max<_OIndexType>());
+ }
+
+ public:
+ template<typename _OIndexType, size_t... _OExtents>
+ requires (sizeof...(_OExtents) == rank())
+ && ((_OExtents == dynamic_extent || _Extents == dynamic_extent
+ || _OExtents == _Extents) && ...)
+ constexpr explicit(_M_ctor_explicit<_OIndexType, _OExtents...>())
+ extents(const extents<_OIndexType, _OExtents...>& __other) noexcept
+ : _M_extents(__other._M_extents)
+ { }
+
+ template<typename... _OIndexTypes>
+ requires (
+ ((sizeof...(_OIndexTypes) == rank()
+ || sizeof...(_OIndexTypes) == rank_dynamic()))
+ && (is_convertible_v<_OIndexTypes, index_type> && ...)
+ && (is_nothrow_constructible_v<index_type, _OIndexTypes> && ...))
+ constexpr explicit extents(_OIndexTypes... __exts) noexcept
+ : _M_extents(__exts...)
+ { }
+
+ template<typename _OIndexType, size_t _Nm>
+ requires (is_convertible_v<const _OIndexType& , index_type>
+ && is_nothrow_constructible_v<index_type, const _OIndexType&>
+ && (_Nm == rank_dynamic() || _Nm == rank()))
+ constexpr explicit(_Nm != rank_dynamic())
+ extents(span<_OIndexType, _Nm> __exts) noexcept
+ : _M_extents(__exts)
+ { }
+
+ template<typename _OIndexType, size_t _Nm>
+ requires (is_convertible_v<const _OIndexType& , index_type>
+ && is_nothrow_constructible_v<index_type, const _OIndexType&>
+ && (_Nm == rank_dynamic() || _Nm == rank()))
+ constexpr explicit(_Nm != rank_dynamic())
+ extents(const array<_OIndexType, _Nm>& __exts) noexcept
+ : _M_extents(__exts)
+ { }
+
+ template<typename _SIndexType, size_t... _SExtents, typename _OIndexType,
+ size_t... _OExtents>
+ friend constexpr bool
+ operator==(const extents&,
+ const extents<_OIndexType, _OExtents...>&) noexcept;
+
+ private:
+ using _ExtentsStorage =
+ typename __detail::__extents_storage<_IndexType, _Extents...>;
+
+ [[no_unique_address]] _ExtentsStorage _M_extents;
+
+ template<typename _OIndexType, size_t... _OExtents>
+ friend class extents;
+ };
+
+ template<typename _SIndexType, size_t... _SExtents, typename _OIndexType,
+ size_t... _OExtents>
+ constexpr bool
+ operator==(const extents<_SIndexType, _SExtents...>& __self,
+ const extents<_OIndexType, _OExtents...>& __other) noexcept
+ {
+ if constexpr (__self.rank() != __other.rank())
+ return false;
+
+ for (size_t __i = 0; __i < __self.rank(); ++__i)
+ if (__self.extent(__i) != __other.extent(__i))
+ return false;
+ return true;
+ }
+
+ namespace __detail
+ {
+ template<typename _IndexType, size_t _Count, size_t _Rank,
+ size_t... _Extents>
+ struct _Dextents
+ {
+ using type = typename _Dextents<_IndexType, _Count+1, _Rank,
+ _Extents..., dynamic_extent>::type;
+ };
+
+ template<typename _IndexType, size_t _Rank, size_t... _Extents>
+ struct _Dextents<_IndexType, _Rank, _Rank, _Extents...>
+ {
+ using type = extents<_IndexType, _Extents...>;
+ };
+
+ template<typename _Tp>
+ struct _DynamicExtent
+ {
+ static constexpr size_t _S_dyn = dynamic_extent;
+ };
+ }
+
+ template<typename _IndexType, size_t _Rank>
+ using dextents = typename __detail::_Dextents<_IndexType, 0, _Rank>::type;
+
+ template<typename... _Integrals>
+ requires (is_convertible_v<_Integrals, size_t> && ...)
+ explicit extents(_Integrals...) ->
+ extents<size_t, __detail::_DynamicExtent<_Integrals>::_S_dyn...>;
+
_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 12253b95c5a..481e39b2821 100644
--- a/libstdc++-v3/src/c++23/std.cc.in
+++ b/libstdc++-v3/src/c++23/std.cc.in
@@ -1825,7 +1825,11 @@ export namespace std
}
}
-// FIXME <mdspan>
+// <mdspan>
+{
+ using std::extents;
+ // FIXME layout_*, default_accessor and mdspan
+}
// 20.2 <memory>
export namespace std
