This patch changes the implementation of operator[], to follow similar
pattern as at, where we normalize argument types and forward to single
overload. The conversion now uses __mdspan::__index_type_cast, instead
of static_assert. This introduces asserts assuring that conversion is
is value preserving.
Finally, __is_multi_index is implemented as local lambda, avoiding
the need to create a local array with copies of the arguments.
libstdc++-v3/ChangeLog:
* include/std/mdspan (__mdspan::__is_multi_index): Removed,
replaced with local lambda in mdspan::operator[].
(__mdspan::operator[]): Implement in terms of single overload
accepting index_type. Use __mdspan::__index_type_cast for type
conversion.
Signed-off-by: Tomasz Kamiński <[email protected]>
---
Tested on x86_64-linux. OK for trunk?
libstdc++-v3/include/std/mdspan | 43 +++++++++++++--------------------
1 file changed, 17 insertions(+), 26 deletions(-)
diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 3476d42a129..68cdcc9b173 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -2906,20 +2906,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
};
#endif
- namespace __mdspan
- {
- template<typename _Extents, typename _IndexType, size_t _Nm>
- constexpr bool
- __is_multi_index(const _Extents& __exts, span<_IndexType, _Nm> __indices)
- {
- static_assert(__exts.rank() == _Nm);
- for (size_t __i = 0; __i < __exts.rank(); ++__i)
- if (__indices[__i] >= __exts.extent(__i))
- return false;
- return true;
- }
- }
-
template<typename _ElementType, typename _Extents,
typename _LayoutPolicy = layout_right,
typename _AccessorPolicy = default_accessor<_ElementType>>
@@ -3056,17 +3042,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr reference
operator[](_OIndexTypes... __indices) const
{
- auto __checked_call = [this](auto... __idxs) -> index_type
- {
- if constexpr (sizeof...(__idxs) > 0)
- __glibcxx_assert(__mdspan::__is_multi_index(extents(),
- span<const index_type, sizeof...(__idxs)>({__idxs...})));
- return _M_mapping(__idxs...);
- };
+ if constexpr (rank() == 0)
+ return _M_accessor.access(_M_handle, _M_mapping());
+ else if constexpr (!(is_same_v<_OIndexTypes, index_type> && ...))
+ return operator[](
+ __mdspan::__index_type_cast<index_type>(std::move(__indices))...);
+ else
+ {
+ auto __is_multi_index = [&]<size_t...
_Counts>(index_sequence<_Counts...>)
+ { return ((__indices < extents().extent(_Counts)) && ...); };
- auto __index = __checked_call(
- static_cast<index_type>(std::move(__indices))...);
- return _M_accessor.access(_M_handle, __index);
+ __glibcxx_assert(__is_multi_index(make_index_sequence<rank()>()));
+ return _M_accessor.access(_M_handle, _M_mapping(__indices...));
+ }
}
template<typename _OIndexType>
@@ -3076,7 +3064,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
auto __call = [&]<size_t... _Counts>(index_sequence<_Counts...>)
-> reference
- { return (*this)[index_type(as_const(__indices[_Counts]))...]; };
+ {
+ return operator[](
+
__mdspan::__index_type_cast<index_type>(as_const(__indices[_Counts]))...);
+ };
return __call(make_index_sequence<rank()>());
}
@@ -3084,7 +3075,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
requires __mdspan::__valid_index_type<const _OIndexType&, index_type>
constexpr reference
operator[](const array<_OIndexType, rank()>& __indices) const
- { return (*this)[span<const _OIndexType, rank()>(__indices)]; }
+ { return operator[](span<const _OIndexType, rank()>(__indices)); }
#if __cplusplus > 202302L
template<__mdspan::__valid_index_type<index_type>... _OIndexTypes>
--
2.53.0
