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[libc++][numeric] P0543R3: Saturation arithmetic (#77967)
Implements: https://wg21.link/P0543R3 - https://eel.is/c++draft/numeric.sat Additional references: - Division: https://eel.is/c++draft/expr.mul#4 - Arithmetic conversions: https://eel.is/c++draft/expr.arith.conv#1 - Clang builtins: https://clang.llvm.org/docs/LanguageExtensions.html#builtin-functions Depends on: #78086 --------- Co-authored-by: Zingam <[email protected]> Co-authored-by: Mark de Wever <[email protected]>
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‎libcxx/docs/FeatureTestMacroTable.rst

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@@ -432,7 +432,7 @@ Status
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--------------------------------------------------- -----------------
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``__cpp_lib_rcu`` *unimplemented*
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--------------------------------------------------- -----------------
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``__cpp_lib_saturation_arithmetic`` *unimplemented*
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``__cpp_lib_saturation_arithmetic`` ``202311L``
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--------------------------------------------------- -----------------
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``__cpp_lib_smart_ptr_owner_equality`` *unimplemented*
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--------------------------------------------------- -----------------

‎libcxx/docs/ReleaseNotes/18.rst

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@@ -75,6 +75,7 @@ Implemented Papers
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- P2909R4 - Fix formatting of code units as integers (Dude, where’s my ``char``?)
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- P2821R5 - ``span.at()``
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- P0521R0 - Proposed Resolution for CA 14 (``shared_ptr`` ``use_count/unique``)
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- P0543R3 - Saturation arithmetic
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- P1759R6 - Native handles and file streams
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- P2868R3 - Remove Deprecated ``std::allocator`` Typedef From C++26
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- P2517R1 - Add a conditional ``noexcept`` specification to ``std::apply``

‎libcxx/docs/Status/Cxx2cPapers.csv

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"`P2714R1 <https://wg21.link/P2714R1>`__","LWG","Bind front and back to NTTP callables","Varna June 2023","","",""
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"`P2630R4 <https://wg21.link/P2630R4>`__","LWG","``submdspan``","Varna June 2023","","",""
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"","","","","","",""
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"`P0543R3 <https://wg21.link/P0543R3>`__","LWG","Saturation arithmetic","Kona November 2023","","",""
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"`P0543R3 <https://wg21.link/P0543R3>`__","LWG","Saturation arithmetic","Kona November 2023","|Complete|","18.0",""
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"`P2407R5 <https://wg21.link/P2407R5>`__","LWG","Freestanding Library: Partial Classes","Kona November 2023","","",""
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"`P2546R5 <https://wg21.link/P2546R5>`__","LWG","Debugging Support","Kona November 2023","","",""
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"`P2905R2 <https://wg21.link/P2905R2>`__","LWG","Runtime format strings","Kona November 2023","|Complete|","18.0","|format| |DR|"

‎libcxx/include/CMakeLists.txt

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@@ -569,6 +569,7 @@ set(files
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__numeric/pstl_reduce.h
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__numeric/pstl_transform_reduce.h
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__numeric/reduce.h
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__numeric/saturation_arithmetic.h
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__numeric/transform_exclusive_scan.h
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__numeric/transform_inclusive_scan.h
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__numeric/transform_reduce.h

‎libcxx/include/__numeric/saturation_arithmetic.h

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// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___NUMERIC_SATURATION_ARITHMETIC_H
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#define _LIBCPP___NUMERIC_SATURATION_ARITHMETIC_H
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#include <__concepts/arithmetic.h>
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#include <__config>
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#include <__utility/cmp.h>
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#include <limits>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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#if _LIBCPP_STD_VER >= 26
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template <__libcpp_integer _Tp>
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_LIBCPP_HIDE_FROM_ABI constexpr _Tp add_sat(_Tp __x, _Tp __y) noexcept {
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if (_Tp __sum; !__builtin_add_overflow(__x, __y, &__sum))
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return __sum;
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// Handle overflow
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if constexpr (__libcpp_unsigned_integer<_Tp>) {
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return std::numeric_limits<_Tp>::max();
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} else {
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// Signed addition overflow
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if (__x > 0)
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// Overflows if (x > 0 && y > 0)
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return std::numeric_limits<_Tp>::max();
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else
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// Overflows if (x < 0 && y < 0)
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return std::numeric_limits<_Tp>::min();
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}
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}
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template <__libcpp_integer _Tp>
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_LIBCPP_HIDE_FROM_ABI constexpr _Tp sub_sat(_Tp __x, _Tp __y) noexcept {
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if (_Tp __sub; !__builtin_sub_overflow(__x, __y, &__sub))
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return __sub;
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// Handle overflow
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if constexpr (__libcpp_unsigned_integer<_Tp>) {
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// Overflows if (x < y)
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return std::numeric_limits<_Tp>::min();
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} else {
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// Signed subtration overflow
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if (__x >= 0)
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// Overflows if (x >= 0 && y < 0)
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return std::numeric_limits<_Tp>::max();
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else
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// Overflows if (x < 0 && y > 0)
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return std::numeric_limits<_Tp>::min();
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}
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}
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template <__libcpp_integer _Tp>
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_LIBCPP_HIDE_FROM_ABI constexpr _Tp mul_sat(_Tp __x, _Tp __y) noexcept {
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if (_Tp __mul; !__builtin_mul_overflow(__x, __y, &__mul))
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return __mul;
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// Handle overflow
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if constexpr (__libcpp_unsigned_integer<_Tp>) {
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return std::numeric_limits<_Tp>::max();
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} else {
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// Signed multiplication overflow
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if ((__x > 0 && __y > 0) || (__x < 0 && __y < 0))
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return std::numeric_limits<_Tp>::max();
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// Overflows if (x < 0 && y > 0) || (x > 0 && y < 0)
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return std::numeric_limits<_Tp>::min();
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}
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}
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template <__libcpp_integer _Tp>
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_LIBCPP_HIDE_FROM_ABI constexpr _Tp div_sat(_Tp __x, _Tp __y) noexcept {
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_LIBCPP_ASSERT_UNCATEGORIZED(__y != 0, "Division by 0 is undefined");
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if constexpr (__libcpp_unsigned_integer<_Tp>) {
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return __x / __y;
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} else {
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// Handle signed division overflow
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if (__x == std::numeric_limits<_Tp>::min() && __y == _Tp{-1})
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return std::numeric_limits<_Tp>::max();
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return __x / __y;
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}
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}
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template <__libcpp_integer _Rp, __libcpp_integer _Tp>
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_LIBCPP_HIDE_FROM_ABI constexpr _Rp saturate_cast(_Tp __x) noexcept {
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// Saturation is impossible edge case when ((min _Rp) < (min _Tp) && (max _Rp) > (max _Tp)) and it is expected to be
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// optimized out by the compiler.
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// Handle overflow
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if (std::cmp_less(__x, std::numeric_limits<_Rp>::min()))
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return std::numeric_limits<_Rp>::min();
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if (std::cmp_greater(__x, std::numeric_limits<_Rp>::max()))
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return std::numeric_limits<_Rp>::max();
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// No overflow
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return static_cast<_Rp>(__x);
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}
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#endif // _LIBCPP_STD_VER >= 26
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___NUMERIC_SATURATION_ARITHMETIC_H

‎libcxx/include/libcxx.imp

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{ include: [ "<__numeric/pstl_reduce.h>", "private", "<numeric>", "public" ] },
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{ include: [ "<__numeric/pstl_transform_reduce.h>", "private", "<numeric>", "public" ] },
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{ include: [ "<__numeric/reduce.h>", "private", "<numeric>", "public" ] },
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{ include: [ "<__numeric/saturation_arithmetic.h>", "private", "<numeric>", "public" ] },
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{ include: [ "<__numeric/transform_exclusive_scan.h>", "private", "<numeric>", "public" ] },
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{ include: [ "<__numeric/transform_inclusive_scan.h>", "private", "<numeric>", "public" ] },
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{ include: [ "<__numeric/transform_reduce.h>", "private", "<numeric>", "public" ] },

‎libcxx/include/module.modulemap.in

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export *
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}
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module std_private_numeric_reduce [system] { header "__numeric/reduce.h" }
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module std_private_numeric_saturation_arithmetic [system] { header "__numeric/saturation_arithmetic.h" }
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module std_private_numeric_transform_exclusive_scan [system] { header "__numeric/transform_exclusive_scan.h" }
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module std_private_numeric_transform_inclusive_scan [system] { header "__numeric/transform_inclusive_scan.h" }
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module std_private_numeric_transform_reduce [system] { header "__numeric/transform_reduce.h" }

‎libcxx/include/numeric

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template<class T>
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constexpr T* midpoint(T* a, T* b); // C++20
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// [numeric.sat], saturation arithmetic
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template<class T>
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constexpr T add_sat(T x, T y) noexcept; // freestanding, Since C++26
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template<class T>
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constexpr T sub_sat(T x, T y) noexcept; // freestanding, Since C++26
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template<class T>
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constexpr T mul_sat(T x, T y) noexcept; // freestanding, Since C++26
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template<class T>
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constexpr T div_sat(T x, T y) noexcept; // freestanding, Since C++26
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template<class T, class U>
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constexpr T saturate_cast(U x) noexcept; // freestanding, Since C++26
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} // std
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*/
@@ -160,6 +172,7 @@ template<class T>
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#include <__numeric/pstl_reduce.h>
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#include <__numeric/pstl_transform_reduce.h>
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#include <__numeric/reduce.h>
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#include <__numeric/saturation_arithmetic.h>
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#include <__numeric/transform_exclusive_scan.h>
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#include <__numeric/transform_inclusive_scan.h>
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#include <__numeric/transform_reduce.h>

‎libcxx/include/version

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// # define __cpp_lib_out_ptr 202311L
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# define __cpp_lib_ratio 202306L
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// # define __cpp_lib_rcu 202306L
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// # define __cpp_lib_saturation_arithmetic 202311L
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# define __cpp_lib_saturation_arithmetic 202311L
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// # define __cpp_lib_smart_ptr_owner_equality 202306L
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# define __cpp_lib_span_at 202311L
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# define __cpp_lib_span_initializer_list 202311L

‎libcxx/modules/std/numeric.inc

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// [numeric.ops.midpoint], midpoint
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using std::midpoint;
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#if _LIBCPP_STD_VER >= 26
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// [numeric.sat], saturation arithmetic
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using std::add_sat;
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using std::div_sat;
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using std::mul_sat;
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using std::saturate_cast;
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using std::sub_sat;
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#endif
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} // namespace std

‎libcxx/test/std/language.support/support.limits/support.limits.general/numeric.version.compile.pass.cpp

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# endif
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# endif
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266-
# if !defined(_LIBCPP_VERSION)
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# ifndef __cpp_lib_saturation_arithmetic
268-
# error "__cpp_lib_saturation_arithmetic should be defined in c++26"
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# endif
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# if __cpp_lib_saturation_arithmetic != 202311L
271-
# error "__cpp_lib_saturation_arithmetic should have the value 202311L in c++26"
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# endif
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# else // _LIBCPP_VERSION
274-
# ifdef __cpp_lib_saturation_arithmetic
275-
# error "__cpp_lib_saturation_arithmetic should not be defined because it is unimplemented in libc++!"
276-
# endif
266+
# ifndef __cpp_lib_saturation_arithmetic
267+
# error "__cpp_lib_saturation_arithmetic should be defined in c++26"
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# endif
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# if __cpp_lib_saturation_arithmetic != 202311L
270+
# error "__cpp_lib_saturation_arithmetic should have the value 202311L in c++26"
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# endif
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#endif // TEST_STD_VER > 23

‎libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp

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# error "__cpp_lib_sample should have the value 201603L in c++26"
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# endif
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7170-
# if !defined(_LIBCPP_VERSION)
7171-
# ifndef __cpp_lib_saturation_arithmetic
7172-
# error "__cpp_lib_saturation_arithmetic should be defined in c++26"
7173-
# endif
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# if __cpp_lib_saturation_arithmetic != 202311L
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# error "__cpp_lib_saturation_arithmetic should have the value 202311L in c++26"
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# endif
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# else // _LIBCPP_VERSION
7178-
# ifdef __cpp_lib_saturation_arithmetic
7179-
# error "__cpp_lib_saturation_arithmetic should not be defined because it is unimplemented in libc++!"
7180-
# endif
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# ifndef __cpp_lib_saturation_arithmetic
7171+
# error "__cpp_lib_saturation_arithmetic should be defined in c++26"
7172+
# endif
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# if __cpp_lib_saturation_arithmetic != 202311L
7174+
# error "__cpp_lib_saturation_arithmetic should have the value 202311L in c++26"
71817175
# endif
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# ifndef __cpp_lib_scoped_lock

‎libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/add_sat.compile.pass.cpp

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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4+
// See https://llvm.org/LICENSE.txt for license information.
5+
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
7+
//===----------------------------------------------------------------------===//
8+
9+
// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
10+
11+
// <numeric>
12+
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// template<class T>
14+
// constexpr T add_sat(T x, T y) noexcept; // freestanding
15+
16+
#include <concepts>
17+
#include <numeric>
18+
19+
#include "test_macros.h"
20+
21+
template <typename T, typename U>
22+
concept CanDo = requires(T x, U y) {
23+
{ std::add_sat(x, y) } -> std::same_as<T>;
24+
};
25+
26+
template <typename T, typename U>
27+
constexpr void test_constraint_success() {
28+
static_assert(CanDo<T, T>);
29+
static_assert(!CanDo<U, T>);
30+
static_assert(!CanDo<T, U>);
31+
}
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33+
template <typename T>
34+
constexpr void test_constraint_fail() {
35+
using I = int;
36+
static_assert(!CanDo<T, T>);
37+
static_assert(!CanDo<I, T>);
38+
static_assert(!CanDo<T, I>);
39+
}
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41+
constexpr void test() {
42+
// Contraint success - Signed
43+
using SI = long long int;
44+
test_constraint_success<signed char, SI>();
45+
test_constraint_success<short int, SI>();
46+
test_constraint_success<signed char, SI>();
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test_constraint_success<short int, SI>();
48+
test_constraint_success<int, SI>();
49+
test_constraint_success<long int, SI>();
50+
test_constraint_success<long long int, int>();
51+
#ifndef TEST_HAS_NO_INT128
52+
test_constraint_success<__int128_t, SI>();
53+
#endif
54+
// Contraint success - Unsigned
55+
using UI = unsigned long long int;
56+
test_constraint_success<unsigned char, UI>();
57+
test_constraint_success<unsigned short int, UI>();
58+
test_constraint_success<unsigned int, UI>();
59+
test_constraint_success<unsigned long int, UI>();
60+
test_constraint_success<unsigned long long int, unsigned int>();
61+
#ifndef TEST_HAS_NO_INT128
62+
test_constraint_success<__uint128_t, UI>();
63+
#endif
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65+
// Contraint failure
66+
test_constraint_fail<bool>();
67+
test_constraint_fail<char>();
68+
#ifndef TEST_HAS_NO_WIDE_CHARACTERS
69+
test_constraint_fail<wchar_t>();
70+
#endif
71+
test_constraint_fail<char8_t>();
72+
test_constraint_fail<char16_t>();
73+
test_constraint_fail<char32_t>();
74+
test_constraint_fail<float>();
75+
test_constraint_fail<double>();
76+
test_constraint_fail<long double>();
77+
}

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