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[libc++] Use saturation builtins directly for {add,sub}_sat #165228

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Nov 4, 2025
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[libc++] Use saturation builtins directly for {add,sub}_sat #165228

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8 changes: 8 additions & 0 deletions libcxx/include/__numeric/saturation_arithmetic.h
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,9 @@ _LIBCPP_BEGIN_NAMESPACE_STD

template <__signed_or_unsigned_integer _Tp>
_LIBCPP_HIDE_FROM_ABI constexpr _Tp __add_sat(_Tp __x, _Tp __y) noexcept {
# if defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER >= 2101
return __builtin_elementwise_add_sat(__x, __y);
# else
if (_Tp __sum; !__builtin_add_overflow(__x, __y, std::addressof(__sum)))
return __sum;
// Handle overflow
Expand All @@ -44,10 +47,14 @@ _LIBCPP_HIDE_FROM_ABI constexpr _Tp __add_sat(_Tp __x, _Tp __y) noexcept {
// Overflows if (x < 0 && y < 0)
return std::numeric_limits<_Tp>::min();
}
# endif
}

template <__signed_or_unsigned_integer _Tp>
_LIBCPP_HIDE_FROM_ABI constexpr _Tp __sub_sat(_Tp __x, _Tp __y) noexcept {
# if defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER >= 2101
return __builtin_elementwise_sub_sat(__x, __y);
# else
if (_Tp __sub; !__builtin_sub_overflow(__x, __y, std::addressof(__sub)))
return __sub;
// Handle overflow
Expand All @@ -63,6 +70,7 @@ _LIBCPP_HIDE_FROM_ABI constexpr _Tp __sub_sat(_Tp __x, _Tp __y) noexcept {
// Overflows if (x < 0 && y > 0)
return std::numeric_limits<_Tp>::min();
}
# endif
}

template <__signed_or_unsigned_integer _Tp>
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