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cppdraft/mdspan/accessor/aligned/members.md

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+[mdspan.accessor.aligned.members]
+
+# 23 Containers library [[containers]](./#containers)
+
+## 23.7 Views [[views]](views#mdspan.accessor.aligned.members)
+
+### 23.7.3 Multidimensional access [[views.multidim]](views.multidim#mdspan.accessor.aligned.members)
+
+#### 23.7.3.5 Accessor policy [[mdspan.accessor]](mdspan.accessor#aligned.members)
+
+#### 23.7.3.5.4 Class template aligned_accessor [[mdspan.accessor.aligned]](mdspan.accessor.aligned#members)
+
+#### 23.7.3.5.4.2 Members [mdspan.accessor.aligned.members]
+
+[🔗](#lib:aligned_accessor,constructor)
+
+`template<class OtherElementType, size_t OtherByteAlignment>
+  constexpr aligned_accessor(aligned_accessor<OtherElementType, OtherByteAlignment>) noexcept;
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24545)
+
+*Constraints*: 
+
+- [(1.1)](#1.1)
+
+  is_convertible_v<OtherElementType(*)[], element_type(*)[]> is true[.](#1.1.sentence-1)
+
+- [(1.2)](#1.2)
+
+  OtherByteAlignment >= byte_alignment is true[.](#1.2.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24555)
+
+*Effects*: None[.](#2.sentence-1)
+
+[🔗](#lib:aligned_accessor,constructor_)
+
+`template<class OtherElementType>
+  constexpr explicit aligned_accessor(default_accessor<OtherElementType>) noexcept;
+`
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24567)
+
+*Constraints*: is_convertible_v<OtherElementType(*)[], element_type(*)[]> is true[.](#3.sentence-1)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24572)
+
+*Effects*: None[.](#4.sentence-1)
+
+[🔗](#lib:access,aligned_accessor)
+
+`constexpr reference access(data_handle_type p, size_t i) const noexcept;
+`
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24583)
+
+*Preconditions*: [0, i + 1) is an accessible range for p and *this[.](#5.sentence-1)
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24587)
+
+*Effects*: Equivalent to: return assume_aligned<byte_alignment>(p)[i];
+
+[🔗](#lib:operator_default_accessor,aligned_accessor)
+
+`template<class OtherElementType>
+  constexpr operator default_accessor<OtherElementType>() const noexcept;
+`
+
+[7](#7)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24599)
+
+*Constraints*: is_convertible_v<element_type(*)[], OtherElementType(*)[]> is true[.](#7.sentence-1)
+
+[8](#8)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24604)
+
+*Effects*: Equivalent to: return {};
+
+[🔗](#lib:offset,aligned_accessor)
+
+`constexpr typename offset_policy::data_handle_type
+  offset(data_handle_type p, size_t i) const noexcept;
+`
+
+[9](#9)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24616)
+
+*Preconditions*: [0, i + 1) is an accessible range for p and *this[.](#9.sentence-1)
+
+[10](#10)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24620)
+
+*Effects*: Equivalent to: return assume_aligned<byte_alignment>(p) + i;

cppdraft/mdspan/accessor/aligned/overview.md

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+[mdspan.accessor.aligned.overview]
+
+# 23 Containers library [[containers]](./#containers)
+
+## 23.7 Views [[views]](views#mdspan.accessor.aligned.overview)
+
+### 23.7.3 Multidimensional access [[views.multidim]](views.multidim#mdspan.accessor.aligned.overview)
+
+#### 23.7.3.5 Accessor policy [[mdspan.accessor]](mdspan.accessor#aligned.overview)
+
+#### 23.7.3.5.4 Class template aligned_accessor [[mdspan.accessor.aligned]](mdspan.accessor.aligned#overview)
+
+#### 23.7.3.5.4.1 Overview [mdspan.accessor.aligned.overview]
+
+namespace std {template<class ElementType, size_t ByteAlignment>struct [aligned_accessor](#lib:aligned_accessor "23.7.3.5.4.1 Overview [mdspan.accessor.aligned.overview]") {using offset_policy = default_accessor<ElementType>; using element_type = ElementType; using reference = ElementType&; using data_handle_type = ElementType*; static constexpr size_t byte_alignment = ByteAlignment; constexpr aligned_accessor() noexcept = default; template<class OtherElementType, size_t OtherByteAlignment>constexpr aligned_accessor( aligned_accessor<OtherElementType, OtherByteAlignment>) noexcept; template<class OtherElementType>constexpr explicit aligned_accessor(default_accessor<OtherElementType>) noexcept; template<class OtherElementType>constexpr operator default_accessor<OtherElementType>() const noexcept; constexpr reference access(data_handle_type p, size_t i) const noexcept; constexpr typename offset_policy::data_handle_type offset( data_handle_type p, size_t i) const noexcept; };}
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24469)
+
+*Mandates*: 
+
+- [(1.1)](#1.1)
+
+byte_alignment is a power of two, and
+
+- [(1.2)](#1.2)
+
+byte_alignment >= alignof(ElementType) is true[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24476)
+
+aligned_accessor meets the accessor policy requirements[.](#2.sentence-1)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24479)
+
+ElementType is required to be a complete object type
+that is neither an abstract class type nor an array type[.](#3.sentence-1)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24483)
+
+Each specialization of aligned_accessor is
+a trivially copyable type that models [semiregular](concepts.object#concept:semiregular "18.6 Object concepts [concepts.object]")[.](#4.sentence-1)
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24487)
+
+[0, n) is an accessible range
+for an object p of type data_handle_type and
+an object of type aligned_accessor if and only if
+
+- [(5.1)](#5.1)
+
+[p, p + n) is a valid range, and,
+
+- [(5.2)](#5.2)
+
+if n is greater than zero,
+then is_sufficiently_aligned<byte_alignment>(p) is true[.](#5.sentence-1)
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/containers.tex#L24499)
+
+[*Example [1](#example-1)*:
+
+The following function compute uses is_sufficiently_aligned to check
+whether a given mdspan with default_accessor has
+a data handle with sufficient alignment
+to be used with aligned_accessor<float, 4 * sizeof(float)>[.](#6.sentence-1)
+
+If so, the function dispatches to
+a function compute_using_fourfold_overalignment that requires fourfold over-alignment of arrays,
+but can therefore use hardware-specific instructions,
+such as four-wide SIMD (Single Instruction Multiple Data) instructions[.](#6.sentence-2)
+
+Otherwise, compute dispatches to a
+possibly less optimized function compute_without_requiring_overalignment that has no over-alignment requirement[.](#6.sentence-3)
+
+void compute_using_fourfold_overalignment( std::mdspan<float, std::dims<1>, std::layout_right,
+ std::aligned_accessor<float, 4 * alignof(float)>> x);
+
+void compute_without_requiring_overalignment( std::mdspan<float, std::dims<1>, std::layout_right> x);
+
+void compute(std::mdspan<float, std::dims<1>> x) {constexpr auto byte_alignment = 4 * sizeof(float); auto accessor = std::aligned_accessor<float, byte_alignment>{}; auto x_handle = x.data_handle(); if (std::is_sufficiently_aligned<byte_alignment>(x_handle)) { compute_using_fourfold_overalignment(std::mdspan{x_handle, x.mapping(), accessor}); } else { compute_without_requiring_overalignment(x); }} — *end example*]