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<mdspan>: Cache fwd-prod-of-extents and rev-prod-of-extents when all extents are static #3715

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Merged
merged 3 commits into from
May 24, 2023
Merged

<mdspan>: Cache fwd-prod-of-extents and rev-prod-of-extents when all extents are static #3715

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e526905
FASTER PRODUCTS!
JMazurkiewicz May 17, 2023
234bacc
Merge branch 'mdspan/main' into mdspan/cache-prods
JMazurkiewicz May 18, 2023
f941929
Merge branch 'feature/mdspan2' into mdspan/cache-prods
JMazurkiewicz May 24, 2023
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107 changes: 83 additions & 24 deletions stl/inc/mdspan
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Original file line number Diff line number Diff line change
Expand Up @@ -231,24 +231,6 @@ public:
}
}

// TRANSITION, LWG ISSUE? I believe that this function should return 'index_type'
_NODISCARD constexpr index_type _Fwd_prod_of_extents(const rank_type _Idx) const noexcept {
index_type _Result = 1;
for (rank_type _Dim = 0; _Dim < _Idx; ++_Dim) {
_Result *= extent(_Dim);
}
return _Result;
}

// TRANSITION, LWG ISSUE? I believe that this function should return 'index_type'
_NODISCARD constexpr index_type _Rev_prod_of_extents(const rank_type _Idx) const noexcept {
index_type _Result = 1;
for (rank_type _Dim = _Idx + 1; _Dim < _Rank; ++_Dim) {
_Result *= extent(_Dim);
}
return _Result;
}

_NODISCARD static consteval bool _Is_index_space_size_representable() {
if constexpr (rank_dynamic() == 0 && rank() > 0) {
return _STD in_range<index_type>((_Extents * ...));
Expand Down Expand Up @@ -293,6 +275,82 @@ inline constexpr bool _Is_extents = false;
template <class _IndexType, size_t... _Args>
inline constexpr bool _Is_extents<extents<_IndexType, _Args...>> = true;

template <class _Extents>
requires _Is_extents<_Extents>
class _Fwd_prod_of_extents {
public:
_NODISCARD static constexpr _Extents::index_type _Calculate(const _Extents& _Exts, const size_t _Idx) noexcept {
if constexpr (_Extents::rank() == 0) {
return 1;
} else {
typename _Extents::index_type _Result = 1;
for (size_t _Dim = 0; _Dim < _Idx; ++_Dim) {
_Result *= _Exts.extent(_Dim);
}
return _Result;
}
}
};

template <class _IndexType, size_t... _Extents>
requires ((_Extents != dynamic_extent) && ...)
class _Fwd_prod_of_extents<extents<_IndexType, _Extents...>> {
private:
using _Ty = extents<_IndexType, _Extents...>;

_NODISCARD static consteval auto _Make_prods() noexcept {
array<typename _Ty::index_type, _Ty::rank() + 1> _Result;
_Result.front() = 1;
for (size_t _Dim = 1; _Dim < _Ty::_Rank + 1; ++_Dim) {
_Result[_Dim] = static_cast<_Ty::index_type>(_Result[_Dim - 1] * _Ty::static_extent(_Dim - 1));
}
return _Result;
}

static constexpr array<typename _Ty::index_type, _Ty::rank() + 1> _Cache = _Make_prods();

public:
_NODISCARD static constexpr _Ty::index_type _Calculate(const _Ty&, const size_t _Idx) noexcept {
return _Cache[_Idx];
}
};

template <class _Extents>
requires _Is_extents<_Extents> && (_Extents::rank() > 0)
class _Rev_prod_of_extents {
public:
_NODISCARD static constexpr _Extents::index_type _Calculate(const _Extents& _Exts, const size_t _Idx) noexcept {
typename _Extents::index_type _Result = 1;
for (size_t _Dim = _Idx + 1; _Dim < _Extents::_Rank; ++_Dim) {
_Result *= _Exts.extent(_Dim);
}
return _Result;
}
};

template <class _IndexType, size_t... _Extents>
requires ((_Extents != dynamic_extent) && ...)
class _Rev_prod_of_extents<extents<_IndexType, _Extents...>> {
private:
using _Ty = extents<_IndexType, _Extents...>;

_NODISCARD static consteval auto _Make_prods() noexcept {
array<typename _Ty::index_type, _Ty::rank()> _Result;
_Result.back() = 1;
for (size_t _Dim = _Ty::_Rank; _Dim-- > 1;) {
_Result[_Dim - 1] = static_cast<_Ty::index_type>(_Result[_Dim] * _Ty::static_extent(_Dim));
}
return _Result;
}

static constexpr array<typename _Ty::index_type, _Ty::rank()> _Cache = _Make_prods();

public:
_NODISCARD static constexpr _Ty::index_type _Calculate(const _Ty&, const size_t _Idx) noexcept {
return _Cache[_Idx];
}
};

template <class _Layout, class _Mapping>
inline constexpr bool _Is_mapping_of =
is_same_v<typename _Layout::template mapping<typename _Mapping::extents_type>, _Mapping>;
Expand Down Expand Up @@ -382,7 +440,7 @@ public:
}

_NODISCARD constexpr index_type required_span_size() const noexcept {
return _Exts._Fwd_prod_of_extents(extents_type::_Rank);
return _Fwd_prod_of_extents<extents_type>::_Calculate(_Exts, extents_type::_Rank);
}

template <class... _IndexTypes>
Expand Down Expand Up @@ -425,7 +483,7 @@ public:
{
_STL_VERIFY(_Idx < extents_type::_Rank,
"Value of i must be less than extents_type::rank() (N4950 [mdspan.layout.left.obs]/6).");
return _Exts._Fwd_prod_of_extents(_Idx);
return _Fwd_prod_of_extents<extents_type>::_Calculate(_Exts, _Idx);
}

template <class _OtherExtents>
Expand Down Expand Up @@ -518,7 +576,7 @@ public:
}

_NODISCARD constexpr index_type required_span_size() const noexcept {
return _Exts._Fwd_prod_of_extents(extents_type::_Rank);
return _Fwd_prod_of_extents<extents_type>::_Calculate(_Exts, extents_type::_Rank);
}

template <class... _IndexTypes>
Expand Down Expand Up @@ -561,7 +619,7 @@ public:
{
_STL_VERIFY(_Idx < extents_type::_Rank,
"Value of i must be less than extents_type::rank() (N4950 [mdspan.layout.right.obs]/6).");
return _Exts._Rev_prod_of_extents(_Idx);
return _Rev_prod_of_extents<extents_type>::_Calculate(_Exts, _Idx);
}

template <class _OtherExtents>
Expand Down Expand Up @@ -742,7 +800,7 @@ public:
if constexpr (extents_type::rank() == 0) {
return true;
} else {
return required_span_size() == _Exts._Fwd_prod_of_extents(extents_type::_Rank);
return required_span_size() == _Fwd_prod_of_extents<extents_type>::_Calculate(_Exts, extents_type::_Rank);
}
}

Expand Down Expand Up @@ -960,7 +1018,8 @@ public:
}

_NODISCARD constexpr size_type size() const noexcept {
return static_cast<size_type>(_Map.extents()._Fwd_prod_of_extents(extents_type::_Rank));
return static_cast<size_type>(
_Fwd_prod_of_extents<extents_type>::_Calculate(_Map.extents(), extents_type::_Rank));
}

_NODISCARD constexpr bool empty() const noexcept {
Expand Down