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[2026-03 LWG Motion 5] P3932R0 Fix LWG4470: Fix integer-from in [simd] #8921

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[2026-03 LWG Motion 5] P3932R0 Fix LWG4470: Fix integer-from in [simd] #8921

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138 changes: 74 additions & 64 deletions source/numerics.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -16542,6 +16542,8 @@

template<class T, class Abi>
constexpr @\exposidnc{simd-size-type} \exposidnc{simd-size-v} = \seebelownc@; // \expos
template<class T, class Abi>
constexpr @\exposidnc{simd-size-type} \exposidnc{mask-size-v} = \seebelownc@; // \expos
template<class T> constexpr size_t @\exposidnc{mask-element-size} = \seebelownc@; // \expos

template<class T>
Expand Down Expand Up @@ -16640,6 +16642,19 @@
otherwise.
\end{itemdescr}

\begin{itemdecl}
template<class T, class Abi>
constexpr @\exposid{simd-size-type} \exposid{mask-size-v}@ = @\seebelow@;
\end{itemdecl}

\begin{itemdescr}
\pnum
\tcode{\exposid{mask-size-v}<T, Abi>} denotes
the width of \tcode{basic_mask<Bytes, Abi>}
if the specialization \tcode{basic_mask<Bytes, Abi>} is enabled, or
\tcode{0} otherwise.
\end{itemdescr}

\begin{itemdecl}
template<class T> constexpr size_t @\exposid{mask-element-size}@ = @\seebelow@;
\end{itemdecl}
Expand Down Expand Up @@ -16781,26 +16796,26 @@
An implementation defines ABI tag types as necessary for the following aliases.

\pnum
\tcode{\exposid{deduce-abi-t}<T, N>} is defined if
\tcode{\exposid{deduce-abi-t}<T, N>} names an ABI tag type if and only if
\begin{itemize}
\item \tcode{T} is a vectorizable type,
\item \tcode{N} is greater than zero, and
\item \tcode{N} is not larger than an implementation-defined maximum.
\end{itemize}
Otherwise, \tcode{\exposid{deduce-abi-t}<T, N>} names an unspecified type.
The \impldef{maximum width for \tcode{vec} and \tcode{mask}} maximum for
\tcode{N} is not smaller than 64 and can differ depending on \tcode{T}.

\pnum
Where present, \tcode{\exposid{deduce-abi-t}<T, N>} names an ABI tag type such
that
If \tcode{\exposid{deduce-abi-t}<T, N>} names an ABI tag type,
the following is \tcode{true}:
\begin{itemize}
\item
\tcode{\exposid{simd-size-v}<T, \exposid{deduce-abi-t}<T, N>>} equals
\tcode{N}, \item \tcode{basic_vec<T, \exposid{deduce-abi-t}<T, N>>} is
enabled\iref{simd.overview}, and
\item
\tcode{basic_mask<sizeof(T),
\exposid{deduce-abi-t}<\exposid{integer-from}<sizeof(T)>, N>>} is enabled.
\item
\tcode{\exposid{simd-size-v}<T, \exposid{deduce-abi-t}<T, N>>}
equals \tcode{N}, and
\item
\tcode{basic_vec<T, \exposid{deduce-abi-t}<T, N>>}
is enabled\iref{simd.overview}.
\end{itemize}

\pnum
Expand Down Expand Up @@ -17043,12 +17058,11 @@
constexpr auto chunk(const basic_mask<Bytes, Abi>& x) noexcept;

template<class T, class... Abis>
constexpr basic_vec<T, @\exposid{deduce-abi-t}@<T, (basic_vec<T, Abis>::size() + ...)>>
cat(const basic_vec<T, Abis>&...) noexcept;
constexpr resize_t<(basic_vec<T, Abis>::size() + ...),
basic_vec<T, Abis...[0]>> cat(const basic_vec<T, Abis>&...) noexcept;
template<size_t Bytes, class... Abis>
constexpr basic_mask<Bytes, @\exposid{deduce-abi-t}@<@\exposid{integer-from}@<Bytes>,
(basic_mask<Bytes, Abis>::size() + ...)>>
cat(const basic_mask<Bytes, Abis>&...) noexcept;
constexpr resize_t<(basic_mask<Bytes, Abis>::size() + ...)>,
basic_mask<Bytes, Abis...[0]>> cat(const basic_mask<Bytes, Abis>&...) noexcept;

// \ref{simd.alg}, algorithms
template<class T, class Abi>
Expand Down Expand Up @@ -17318,9 +17332,9 @@
template<@\exposconcept{simd-complex}@ V> constexpr V pow(const V& x, const V& y);

// \ref{simd.mask.class}, class template \tcode{basic_mask}
template<size_t Bytes, class Abi = @\exposid{native-abi}@<@\exposid{integer-from}@<Bytes>>> class basic_mask;
template<size_t Bytes, class Abi> class basic_mask;
template<class T, @\exposid{simd-size-type}@ N = @\exposid{simd-size-v}@<T, @\exposid{native-abi}@<T>>>
using @\libmember{mask}{simd}@ = basic_mask<sizeof(T), @\exposid{deduce-abi-t}@<T, N>>;
using @\libmember{mask}{simd}@ = vec<T, N>::mask_type;

// \ref{simd.mask.reductions}, reductions
template<size_t Bytes, class Abi>
Expand Down Expand Up @@ -17508,8 +17522,7 @@
\begin{itemize}
\item \tcode{V} is a data-parallel type,
\item \tcode{T} is a vectorizable type, and
\item \tcode{\exposid{deduce-abi-t}<T, V::size()>} has a member type
\tcode{type}.
\item \tcode{\exposid{deduce-abi-t}<T, V::size()>} names an ABI tag type.
\end{itemize}

\pnum
Expand All @@ -17534,34 +17547,33 @@

\begin{itemdescr}
\pnum
Let \tcode{T} denote
Let \tcode{Abi1} denote an ABI tag
\begin{itemize}
\item
\tcode{typename V::value_type} if \tcode{V} is a specialization of
\tcode{basic_vec},
such that \tcode{\exposid{simd-size-v}<typename V::value_type, Abi1>}
equals \tcode{N} if \tcode{V} is a specialization of \tcode{basic_vec},
\item
otherwise \tcode{\exposid{integer-from}<\exposid{mask-element-size}<V>>} if
\tcode{V} is a specialization of \tcode{basic_mask}.
otherwise such that
\tcode{\exposid{mask-size-v}<\exposid{mask-element-size}<V>, Abi1>}
equals \tcode{N} if \tcode{V} is a specialization of \tcode{basic_mask}.
\end{itemize}

\pnum
The member \tcode{type} is present if and only if
\begin{itemize}
\item \tcode{V} is a data-parallel type, and
\item \tcode{\exposid{deduce-abi-t}<T, N>} has a member type \tcode{type}.
\item
\tcode{V} is a data-parallel type, and
\item
there exists at least one ABI tag
that satisfies the above constraints for \tcode{Abi1}.
\end{itemize}

\pnum
If \tcode V is a specialization of \tcode{basic_vec}, let \tcode{Abi1} denote an
ABI tag such that \tcode{basic_vec<T, Abi1>::\brk{}size()} equals \tcode{N}.
If \tcode V is a specialization of \tcode{basic_mask}, let \tcode{Abi1}
denote an ABI tag such that \tcode{basic_mask<sizeof(T), Abi1>::size()} equals \tcode{N}.

\pnum
Where present, the member typedef \tcode{type} names \tcode{basic_vec<T, Abi1>}
if \tcode V is a specialization of \tcode{basic_vec} or
\tcode{basic_mask<sizeof(T), Abi1>} if \tcode V is a specialization of
\tcode{basic_mask}.
Where present, the member typedef \tcode{type} names
\tcode{basic_vec<typename V::value_type, Abi1>}
if \tcode{V} is a specialization of \tcode{basic_vec}, or
\tcode{basic_mask<\exposid{mask-element-size}<V>, Abi1>}
if \tcode{V} is a specialization of \tcode{basic_mask}.
\end{itemdescr}

\rSec2[simd.flags]{Load and store flags}
Expand Down Expand Up @@ -17986,7 +17998,8 @@
\begin{itemize}
\item
enabled, if \tcode{T} is a vectorizable type, and there exists value
\tcode{N} in the range \crange{1}{64}, such that \tcode{Abi} is
\tcode{N} in the range \crange{1}{64},
such that \tcode{Abi} names the ABI tag denoted by
\tcode{\exposid{deduce-abi-t}<T, N>},
\item
otherwise, disabled, if \tcode{T} is not a vectorizable type,
Expand All @@ -18001,10 +18014,22 @@
In addition only the \tcode{value_type}, \tcode{abi_type}, and
\tcode{mask_type} members are present.

If \tcode{basic_vec<T, Abi>} is enabled, then \tcode{basic_vec<T, Abi>} is
trivially copyable, default-initialization of an object of such a type
default-initializes all elements, and value-initialization value-initializes
all elements\iref{dcl.init.general}.
If \tcode{basic_vec<T, Abi>} is enabled, then
\begin{itemize}
\item
\tcode{basic_vec<T, Abi>} is trivially copyable,
\item
default-initialization of an object of such a type
default-initializes all elements,
\item
value-initialization value-initializes all elements\iref{dcl.init.general},
\item
\tcode{basic_vec<T, Abi>::mask_type} is an alias
for an enabled specialization of \tcode{basic_mask}, and
\item
\tcode{basic_vec<T, Abi>::size()} is equal to
\tcode{basic_vec<T, Abi>::mask_type::size()}.
\end{itemize}

\pnum
\recommended
Expand Down Expand Up @@ -19550,28 +19575,14 @@
\indexlibrarymember{cat}{simd}
\begin{itemdecl}
template<class T, class... Abis>
constexpr vec<T, (basic_vec<T, Abis>::size() + ...)>
cat(const basic_vec<T, Abis>&... xs) noexcept;
constexpr resize_t<(basic_vec<T, Abis>::size() + ...),
basic_vec<T, Abis...[0]>> cat(const basic_vec<T, Abis>&... xs) noexcept;
template<size_t Bytes, class... Abis>
constexpr basic_mask<Bytes, @\exposid{deduce-abi-t}@<@\exposid{integer-from}@<Bytes>,
(basic_mask<Bytes, Abis>::size() + ...)>>
cat(const basic_mask<Bytes, Abis>&... xs) noexcept;
constexpr resize_t<(basic_mask<Bytes, Abis>::size() + ...),
basic_mask<Bytes, Abis...[0]>> cat(const basic_mask<Bytes, Abis>&... xs) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
\constraints
\begin{itemize}
\item
For the first overload \tcode{vec<T, (basic_vec<T, Abis>::size() + ...)>}
is enabled.
\item
For the second overload
\tcode{basic_mask<Bytes,
\exposid{deduce-abi-t}<\exposid{integer-from}<Bytes>,
(basic_mask<Bytes, Abis>::size() + ...)>>} is enabled.
\end{itemize}

\pnum
\returns
A data-parallel object initialized with the concatenated values in the
Expand Down Expand Up @@ -20385,8 +20396,7 @@
constexpr default_sentinel_t @\libmember{end}{basic_mask}@() const noexcept { return {}; }
constexpr default_sentinel_t @\libmember{cend}{basic_mask}@() const noexcept { return {}; }

static constexpr integral_constant<@\exposid{simd-size-type}@, @\exposid{simd-size-v}@<@\exposid{integer-from}@<Bytes>, Abi>>
@\libmember{size}{basic_mask}@ {};
static constexpr integral_constant<@\exposid{simd-size-type}@, @\exposid{mask-size-v}@<Bytes, Abi>> @\libmember{size}{basic_mask}@ {};

constexpr basic_mask() noexcept = default;

Expand Down Expand Up @@ -20474,9 +20484,9 @@
is equal to \tcode{sizeof(T)},
\item
otherwise, enabled, if there exists a vectorizable type \tcode{T} and a
value \tcode{N} in the range \crange{1}{64} such that \tcode{Bytes} is equal
to \tcode{sizeof(T)} and \tcode{Abi} is \tcode{\exposid{deduce-abi-t}<T,
N>},
value \tcode{N} in the range \crange{1}{64}
such that \tcode{Bytes} is equal to \tcode{sizeof(T)} and
\tcode{Abi} names the ABI tag denoted by \tcode{\exposid{decude-abi-t}<T, N>},
\item
otherwise, it is \impldef{set of enabled \tcode{basic_mask<Bytes, Abi>}
specializations} if such a specialization is enabled.
Expand Down
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