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P3480R6 std::simd is a range #7998

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d874f01
P2876R3 Proposal to extend std::simd with more constructors and acces…
mattkretz Jun 21, 2025
6fdb0fc
[simd.mask.namedconv] Use math expression for precondition
mattkretz Jun 21, 2025
9aa2737
[simd.mask.ctor] Remove space before \iref
mattkretz Jun 23, 2025
b4176cc
P3480R6 std::simd is a range
mattkretz Jun 21, 2025
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340 changes: 340 additions & 0 deletions source/numerics.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -17187,6 +17187,262 @@
specialization \tcode{\exposid{overaligned-flag}<std::min(N1, N2)>}.
\end{itemdescr}

\rSec2[simd.iterator]{Class \exposid{simd-iterator}}
\begin{codeblock}
namespace std::datapar {
template<class V>
class @\exposidnc{simd-iterator}@ { // \expos
V* @\exposidnc{data_}@ = nullptr; // \expos
@\exposidnc{simd-size-type} \exposidnc{offset_}@ = 0; // \expos

constexpr @\exposid{simd-iterator}@(V& d, @\exposid{simd-size-type}@ off) noexcept; // \expos

public:
using value_type = typename V::value_type;
using iterator_category = input_iterator_tag;
using iterator_concept = random_access_iterator_tag;
using difference_type = @\exposid{simd-size-type}@;

constexpr @\exposid{simd-iterator}@() = default;

constexpr @\exposid{simd-iterator}@(const @\exposid{simd-iterator}@&) = default;
constexpr @\exposid{simd-iterator}@& operator=(const @\exposid{simd-iterator}@&) = default;

constexpr @\exposid{simd-iterator}@(const @\exposid{simd-iterator}@<remove_const_t<V>>&) requires is_const_v<V>;

constexpr value_type operator*() const;

constexpr @\exposid{simd-iterator}@& operator++();
constexpr @\exposid{simd-iterator}@ operator++(int);
constexpr @\exposid{simd-iterator}@& operator--();
constexpr @\exposid{simd-iterator}@ operator--(int);

constexpr @\exposid{simd-iterator}@& operator+=(difference_type n);
constexpr @\exposid{simd-iterator}@& operator-=(difference_type n);

constexpr value_type operator[](difference_type n) const;

friend constexpr bool operator==(@\exposid{simd-iterator}@ a, @\exposid{simd-iterator}@ b) = default;
friend constexpr bool operator==(@\exposid{simd-iterator}@ a, default_sentinel_t) noexcept;
friend constexpr auto operator<=>(@\exposid{simd-iterator}@ a, @\exposid{simd-iterator}@ b);

friend constexpr @\exposid{simd-iterator}@ operator+(@\exposid{simd-iterator}@ i, difference_type n);
friend constexpr @\exposid{simd-iterator}@ operator+(difference_type n, @\exposid{simd-iterator}@ i);
friend constexpr @\exposid{simd-iterator}@ operator-(@\exposid{simd-iterator}@ i, difference_type n);

friend constexpr difference_type operator-(@\exposid{simd-iterator}@ a, @\exposid{simd-iterator}@ b);
friend constexpr difference_type operator-(@\exposid{simd-iterator}@ i, default_sentinel_t) noexcept;
friend constexpr difference_type operator-(default_sentinel_t, @\exposid{simd-iterator}@ i) noexcept;
};
}
\end{codeblock}

\begin{itemdecl}
constexpr @\exposid{simd-iterator}@(V& d, @\exposid{simd-size-type}@ off) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Initializes \exposid{data_} with \tcode{addressof(d)} and \exposid{offset_} with \tcode{off}.
\end{itemdescr}

\begin{itemdecl}
constexpr @\exposid{simd-iterator}@(const @\exposid{simd-iterator}@<remove_const_t<V>>& i) requires is_const_v<V>;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Initializes \exposid{data_} with \tcode{i.\exposid{data_}} and \exposid{offset_} with \tcode{i.\exposid{offset_}}.
\end{itemdescr}

\begin{itemdecl}
constexpr value_type operator*() const;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return (*\exposid{data_})[\exposid{offset_}];}
\end{itemdescr}

\begin{itemdecl}
constexpr @\exposid{simd-iterator}@& operator++();
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return *this += 1;}
\end{itemdescr}

\begin{itemdecl}
constexpr @\exposid{simd-iterator}@ operator++(int);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to:
\begin{codeblock}
@\exposid{simd-iterator}@ tmp = *this;
*this += 1;
return tmp;
\end{codeblock}
\end{itemdescr}

\begin{itemdecl}
constexpr @\exposid{simd-iterator}@& operator--();
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return *this -= 1;}
\end{itemdescr}

\begin{itemdecl}
constexpr @\exposid{simd-iterator}@ operator--(int);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to:
\begin{codeblock}
@\exposid{simd-iterator}@ tmp = *this;
*this -= 1;
return tmp;
\end{codeblock}
\end{itemdescr}

\begin{itemdecl}
constexpr @\exposid{simd-iterator}@& operator+=(difference_type n);
\end{itemdecl}

\begin{itemdescr}
\pnum
\expects
\tcode{\exposid{offset_} + n} is in the range \crange{0}{V::size()}.

\pnum
\effects
Equivalent to:
\begin{codeblock}
@\exposid{offset_}@ += n;
return *this;
\end{codeblock}
\end{itemdescr}

\begin{itemdecl}
constexpr @\exposid{simd-iterator}@& operator-=(difference_type n);
\end{itemdecl}

\begin{itemdescr}
\pnum
\expects
\tcode{\exposid{offset_} - n} is in the range \crange{0}{V::size()}.

\pnum
\effects
Equivalent to:
\begin{codeblock}
@\exposid{offset_}@ -= n;
return *this;
\end{codeblock}
\end{itemdescr}

\begin{itemdecl}
constexpr value_type operator[](difference_type n) const;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return (*\exposid{data_})[\exposid{offset_} + n];}
\end{itemdescr}

\begin{itemdecl}
friend constexpr bool operator==(@\exposid{simd-iterator}@ i, default_sentinel_t) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return i.\exposid{offset_} == V::size();}
\end{itemdescr}

\begin{itemdecl}
friend constexpr auto operator<=>(@\exposid{simd-iterator}@ a, @\exposid{simd-iterator}@ b);
\end{itemdecl}

\begin{itemdescr}
\pnum
\expects
\tcode{a.\exposid{data_} == b.\exposid{data_}} is \tcode{true}.

\pnum
\effects
Equivalent to: \tcode{return a.\exposid{offset_} <=> b.\exposid{offset_};}
\end{itemdescr}

\begin{itemdecl}
friend constexpr @\exposid{simd-iterator}@ operator+(@\exposid{simd-iterator}@ i, difference_type n);
friend constexpr @\exposid{simd-iterator}@ operator+(difference_type n, @\exposid{simd-iterator}@ i);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return i += n;}
\end{itemdescr}

\begin{itemdecl}
friend constexpr @\exposid{simd-iterator}@ operator-(@\exposid{simd-iterator}@ i, difference_type n);
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return i -= n;}
\end{itemdescr}

\begin{itemdecl}
friend constexpr difference_type operator-(@\exposid{simd-iterator}@ a, @\exposid{simd-iterator}@ b);
\end{itemdecl}

\begin{itemdescr}
\pnum
\expects
\tcode{a.\exposid{data_} == b.\exposid{data_}} is \tcode{true}.

\pnum
\effects
Equivalent to: \tcode{return a.\exposid{offset_} - b.\exposid{offset_};}
\end{itemdescr}

\begin{itemdecl}
friend constexpr difference_type operator-(@\exposid{simd-iterator}@ i, default_sentinel_t) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return i.\exposid{offset_} - V::size();}
\end{itemdescr}


\begin{itemdecl}
friend constexpr difference_type operator-(default_sentinel_t, @\exposid{simd-iterator}@ i) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Equivalent to: \tcode{return V::size() - i.\exposid{offset_};}
\end{itemdescr}

\rSec2[simd.class]{Class template \tcode{basic_simd}}

\rSec3[simd.overview]{Class template \tcode{basic_simd} overview}
Expand All @@ -17198,6 +17454,14 @@
using value_type = T;
using mask_type = basic_simd_mask<sizeof(T), Abi>;
using abi_type = Abi;
using iterator = \exposid{simd-iterator}<basic_simd>;
using const_iterator = \exposid{simd-iterator}<const basic_simd>;

constexpr iterator begin() noexcept { return {*this, 0}; }
constexpr const_iterator begin() const noexcept { return {*this, 0}; }
constexpr const_iterator cbegin() const noexcept { return {*this, 0}; }
constexpr default_sentinel_t end() const noexcept { return {}; }
constexpr default_sentinel_t cend() const noexcept { return {}; }
Comment on lines +17457 to +17464
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@Eisenwave Eisenwave Jun 23, 2025 •
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Seeing that these are entirely defined within the synopsis, we should have some \indexlibrarymember macros above.

Same for basic_simd_mask.

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We have \libmember for inline indexing inside codeblocks. "grep" for examples.

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The members of simd-iterator do not get indexed, right? (because it's an exposition-only type? OTOH its members are public API.)

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Also, looking at some more examples of indexing, there's a lot of index macros missing for [simd]. I guess I should add all those as editorial commit after the motions.

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Looking at ranges.tex, the exposition-only iterators are fully indexed. So I guess I could do that as well.
I'll close this PR in favor of a single PR that includes all 4 simd motions ASAP.


static constexpr integral_constant<@\exposid{simd-size-type}@, @\exposid{simd-size-v}@<T, Abi>> size {};

Expand Down Expand Up @@ -19084,6 +19348,14 @@
public:
using value_type = bool;
using abi_type = Abi;
using iterator = \exposid{simd-iterator}<basic_simd_mask>;
using const_iterator = \exposid{simd-iterator}<const basic_simd_mask>;

constexpr iterator begin() noexcept { return {*this, 0}; }
constexpr const_iterator begin() const noexcept { return {*this, 0}; }
constexpr const_iterator cbegin() const noexcept { return {*this, 0}; }
constexpr default_sentinel_t end() const noexcept { return {}; }
constexpr default_sentinel_t cend() const noexcept { return {}; }

static constexpr integral_constant<@\exposid{simd-size-type}@, @\exposid{simd-size-v}@<@\exposid{integer-from}@<Bytes>, Abi>>
size {};
Expand All @@ -19095,6 +19367,8 @@
template<size_t UBytes, class UAbi>
constexpr explicit basic_simd_mask(const basic_simd_mask<UBytes, UAbi>&) noexcept;
template<class G> constexpr explicit basic_simd_mask(G&& gen) noexcept;
constexpr basic_simd_mask(const bitset<size()>& b) noexcept;
constexpr explicit basic_simd_mask(@\libconcept{unsigned_integral}@ auto val) noexcept;

// \ref{simd.mask.subscr}, \tcode{basic_simd_mask} subscript operators
constexpr value_type operator[](@\exposid{simd-size-type}@) const;
Expand All @@ -19109,6 +19383,10 @@
template<class U, class A>
constexpr explicit(sizeof(U) != Bytes) operator basic_simd<U, A>() const noexcept;

// \ref{simd.mask.namedconv}, \tcode{basic_simd_mask} named type convertors
constexpr bitset<size()> to_bitset() const noexcept;
constexpr unsigned long long to_ullong() const;

// \ref{simd.mask.binary}, \tcode{basic_simd_mask} binary operators
friend constexpr basic_simd_mask
operator&&(const basic_simd_mask&, const basic_simd_mask&) noexcept;
Expand Down Expand Up @@ -19241,6 +19519,31 @@
\tcode{gen} is invoked exactly once for each $i$, in increasing order of $i$.
\end{itemdescr}

\begin{itemdecl}
constexpr basic_simd_mask(const bitset<size()>& b) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Initializes the $i^\text{th}$ element with \tcode{b[$i$]} for all $i$ in the
range \range{0}{size()}.
\end{itemdescr}

\begin{itemdecl}
constexpr explicit basic_simd_mask(@\libconcept{unsigned_integral}@ auto val) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\effects
Initializes the first $M$ elements to the corresponding bit values in
\tcode{val}, where $M$ is the smaller of \tcode{size()} and the number of bits in
the value representation\iref{basic.types.general} of the type of \tcode{val}. If
$M$ is less than \tcode{size()}, the remaining elements are initialized to
zero.
\end{itemdescr}

\rSec3[simd.mask.subscr]{\tcode{basic_simd_mask} subscript operator}

\begin{itemdecl}
Expand Down Expand Up @@ -19299,6 +19602,43 @@
\tcode{static_cast<U>(operator[]($i$))}.
\end{itemdescr}

\rSec3[simd.mask.namedconv]{\tcode{basic_simd_mask} named conversion operators}

\begin{itemdecl}
constexpr bitset<size()> to_bitset() const noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\returns
A \tcode{bitset<size()>} object where the $i^\text{th}$ element is initialized to
\tcode{operator[]($i$)} for all $i$ in the range \range{0}{size()}.
\end{itemdescr}

\begin{itemdecl}
constexpr unsigned long long to_ullong() const;
\end{itemdecl}

\begin{itemdescr}
\pnum
Let $N$ be the width of \tcode{unsigned long long}.

\pnum
\expects
\begin{itemize}
\item \tcode{size()} $\le N$, or
\item for all $i$ in the range \range{$N$}{size()}, \tcode{operator[]($i$)} returns \tcode{false}.
\end{itemize}

\pnum
\returns
The integral value corresponding to the bits in \tcode{*this}.

\pnum
\throws
Nothing.
\end{itemdescr}

\rSec2[simd.mask.nonmembers]{Non-member operations}

\rSec3[simd.mask.binary]{\tcode{basic_simd_mask} binary operators}
Expand Down
2 changes: 1 addition & 1 deletion source/support.tex
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -805,7 +805,7 @@
#define @\defnlibxname{cpp_lib_shared_ptr_weak_type}@ 201606L // also in \libheader{memory}
#define @\defnlibxname{cpp_lib_shared_timed_mutex}@ 201402L // also in \libheader{shared_mutex}
#define @\defnlibxname{cpp_lib_shift}@ 202202L // also in \libheader{algorithm}
#define @\defnlibxname{cpp_lib_simd}@ 202502L // also in \libheader{simd}
#define @\defnlibxname{cpp_lib_simd}@ 202506L // also in \libheader{simd}
#define @\defnlibxname{cpp_lib_simd_complex}@ 202502L // also in \libheader{simd}
#define @\defnlibxname{cpp_lib_smart_ptr_for_overwrite}@ 202002L // also in \libheader{memory}
#define @\defnlibxname{cpp_lib_smart_ptr_owner_equality}@ 202306L // also in \libheader{memory}
Expand Down