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[2026-03 LWG Motion 3] P3690R1 Consistency fix: Make simd reductions SIMD-generic #8885

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[2026-03 LWG Motion 3] P3690R1 Consistency fix: Make simd reductions SIMD-generic #8885

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81 changes: 81 additions & 0 deletions source/numerics.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -16865,6 +16865,12 @@
const basic_vec<T, Abi>& x, const typename basic_vec<T, Abi>::mask_type& mask,
BinaryOperation binary_op = {}, type_identity_t<T> identity_element = @\seebelow@);

template<class T, class BinaryOperation = plus<>>
constexpr T reduce(const T&, BinaryOperation = {});
template<class T, class BinaryOperation = plus<>>
constexpr T reduce(const T& x, same_as<bool> auto mask, BinaryOperation binary_op = {},
type_identity_t<T> identity_element = @\seebelow@);

template<class T, class Abi>
constexpr T reduce_min(const basic_vec<T, Abi>&) noexcept;
template<class T, class Abi>
Expand All @@ -16876,6 +16882,11 @@
constexpr T reduce_max(const basic_vec<T, Abi>&,
const typename basic_vec<T, Abi>::mask_type&) noexcept;

template<class T> constexpr T reduce_min(const T&) noexcept;
template<class T> constexpr T reduce_min(const T&, same_as<bool> auto) noexcept;
template<class T> constexpr T reduce_max(const T&) noexcept;
template<class T> constexpr T reduce_max(const T&, same_as<bool> auto) noexcept;

// \ref{simd.loadstore}, load and store functions
template<class V = @\seebelow@, ranges::@\libconcept{contiguous_range}@ R, class... Flags>
requires ranges::@\libconcept{sized_range}@<R>
Expand Down Expand Up @@ -18715,6 +18726,50 @@
\end{itemize}
\end{itemdescr}

\begin{itemdecl}
template<class T, class BinaryOperation = plus<>>
constexpr T reduce(const T& x, BinaryOperation binary_op = {});
template<class T, class BinaryOperation = plus<>>
constexpr T reduce(const T& x, same_as<bool> auto mask, BinaryOperation binary_op = {},
type_identity_t<T> identity_element = @\seebelow@);
\end{itemdecl}

\begin{itemdescr}
\pnum
Let \tcode{mask} be \tcode{true} for the overload with no \tcode{mask} parameter.

\pnum
\constraints
\begin{itemize}
\item \tcode{T} is vectorizable.
\item \tcode{BinaryOperation} models
\tcode{\exposconcept{reduction-binary-operation}<T>}.
\item An argument for \tcode{identity_element} is provided for the invocation,
unless \tcode{BinaryOperation} is one of \code{plus<>}, \code{multiplies<>},
\code{bit_and<>}, \code{bit_or<>}, or \code{bit_xor<>}.
\end{itemize}

\pnum
\returns
If \tcode{mask} is \tcode{false}, returns \tcode{identity_element}.
Otherwise, returns \tcode{x}.

\pnum
\throws
Nothing.

\pnum
\remarks
The default argument for \code{identity_element} is equal to
\begin{itemize}
\item \tcode{T()} if \code{BinaryOperation} is \code{plus<>},
\item \tcode{T(1)} if \code{BinaryOperation} is \code{multiplies<>},
\item \tcode{T(\~{}T())} if \code{BinaryOperation} is \code{bit_and<>},
\item \tcode{T()} if \code{BinaryOperation} is \code{bit_or<>}, or
\item \tcode{T()} if \code{BinaryOperation} is \code{bit_xor<>}.
\end{itemize}
\end{itemdescr}

\indexlibrarymember{reduce_min}{simd}
\begin{itemdecl}
template<class T, class Abi> constexpr T reduce_min(const basic_vec<T, Abi>& x) noexcept;
Expand Down Expand Up @@ -18789,6 +18844,32 @@
\tcode{mask}.
\end{itemdescr}

\begin{itemdecl}
template<class T> constexpr T reduce_min(const T& x) noexcept;
template<class T> constexpr T reduce_min(const T& x, same_as<bool> auto mask) noexcept;
template<class T> constexpr T reduce_max(const T& x) noexcept;
template<class T> constexpr T reduce_max(const T& x, same_as<bool> auto mask) noexcept;
\end{itemdecl}

\begin{itemdescr}
\pnum
Let \tcode{mask} be \tcode{true} for the overloads with no \tcode{mask} parameter.

\pnum
\constraints
\begin{itemize}
\item \tcode{T} is vectorizable.
\item \tcode{T} models \tcode{totally_ordered}.
\end{itemize}

\pnum
\returns
If \tcode{mask} is \tcode{false}, returns \tcode{numeric_limits<T>::max()} for
\tcode{reduce_min} and \tcode{numeric_limits<T>::lowest()} for
\tcode{reduce_max}.
Otherwise, returns \tcode{x}.
\end{itemdescr}

\rSec3[simd.loadstore]{Load and store functions}

\indexlibrarymember{unchecked_load}{simd}
Expand Down
2 changes: 1 addition & 1 deletion source/support.tex
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Original file line number Diff line number Diff line change
Expand Up @@ -832,7 +832,7 @@
#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}@ 202511L // also in \libheader{simd}
#define @\defnlibxname{cpp_lib_simd}@ 202603L // also in \libheader{simd}
#define @\defnlibxname{cpp_lib_simd_complex}@ 202502L // also in \libheader{simd}
#define @\defnlibxname{cpp_lib_simd_permutations}@ 202506L // also in \libheader{simd}
#define @\defnlibxname{cpp_lib_smart_ptr_for_overwrite}@ 202002L // also in \libheader{memory}
Expand Down
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