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[libc++] Workaround for a bug of overloads in MS UCRT's <math.h> (#149234)
MS UCRT seems confused on the status of LWG1327, and still provides pre-LWG1327 overload set the related math functions, which can't handle integer types as required. It is probably that UCRT won't fixed this in a near future, per https://developercommunity.visualstudio.com/t/10294165. Before C++20, libc++ worked around this bug by relying on `-fdelayed-template-parsing`. However, this non-conforming option is off by default since C++20. I think we should use `requires` instead. --------- Co-authored-by: Louis Dionne <[email protected]>
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‎libcxx/include/__math/traits.h

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@@ -189,6 +189,82 @@ template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_ar
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return __builtin_isunordered((type)__x, (type)__y);
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}
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// MS UCRT incorrectly defines some functions in a way not working with integer types. Until C++20, this was worked
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// around by -fdelayed-template-parsing. Since C++20, we can use standard feature "requires" instead.
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// TODO: Remove the workaround once UCRT fixes these functions. Note that this doesn't seem planned as of 2025-07 per
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// https://developercommunity.visualstudio.com/t/10294165.
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#if defined(_LIBCPP_MSVCRT) && _LIBCPP_STD_VER >= 20
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namespace __ucrt {
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template <class _A1>
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requires is_integral_v<_A1>
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[[nodiscard]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isfinite(_A1) noexcept {
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return true;
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}
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template <class _A1>
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requires is_integral_v<_A1>
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[[nodiscard]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isinf(_A1) noexcept {
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return false;
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}
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template <class _A1>
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requires is_integral_v<_A1>
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[[nodiscard]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnan(_A1) noexcept {
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return false;
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}
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template <class _A1>
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requires is_integral_v<_A1>
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[[nodiscard]] inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(_A1 __x) noexcept {
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return __x != 0;
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}
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template <class _A1, class _A2>
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requires is_arithmetic_v<_A1> && is_arithmetic_v<_A2>
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[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool isgreater(_A1 __x, _A2 __y) noexcept {
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using type = __promote_t<_A1, _A2>;
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return __builtin_isgreater((type)__x, (type)__y);
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}
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template <class _A1, class _A2>
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requires is_arithmetic_v<_A1> && is_arithmetic_v<_A2>
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[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool isgreaterequal(_A1 __x, _A2 __y) noexcept {
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using type = __promote_t<_A1, _A2>;
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return __builtin_isgreaterequal((type)__x, (type)__y);
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}
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template <class _A1, class _A2>
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requires is_arithmetic_v<_A1> && is_arithmetic_v<_A2>
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[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool isless(_A1 __x, _A2 __y) noexcept {
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using type = __promote_t<_A1, _A2>;
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return __builtin_isless((type)__x, (type)__y);
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}
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template <class _A1, class _A2>
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requires is_arithmetic_v<_A1> && is_arithmetic_v<_A2>
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[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool islessequal(_A1 __x, _A2 __y) noexcept {
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using type = __promote_t<_A1, _A2>;
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return __builtin_islessequal((type)__x, (type)__y);
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}
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template <class _A1, class _A2>
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requires is_arithmetic_v<_A1> && is_arithmetic_v<_A2>
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[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool islessgreater(_A1 __x, _A2 __y) noexcept {
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using type = __promote_t<_A1, _A2>;
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return __builtin_islessgreater((type)__x, (type)__y);
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}
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template <class _A1, class _A2>
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requires is_arithmetic_v<_A1> && is_arithmetic_v<_A2>
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[[nodiscard]] inline _LIBCPP_HIDE_FROM_ABI bool isunordered(_A1 __x, _A2 __y) noexcept {
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using type = __promote_t<_A1, _A2>;
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return __builtin_isunordered((type)__x, (type)__y);
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}
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} // namespace __ucrt
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#endif
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} // namespace __math
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_LIBCPP_END_NAMESPACE_STD

‎libcxx/include/math.h

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@@ -429,6 +429,25 @@ using std::__math::isnormal;
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using std::__math::isunordered;
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# endif // _LIBCPP_MSVCRT
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# if defined(_LIBCPP_MSVCRT) && _LIBCPP_STD_VER >= 20
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// MS UCRT incorrectly defines some functions in a way not working with integer types. Until C++20, this was worked
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// around by -fdelayed-template-parsing. Since C++20, we can use standard feature "requires" instead.
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// TODO: Remove the workaround once UCRT fixes these functions. Note that this doesn't seem planned as of 2025-07 per
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// https://developercommunity.visualstudio.com/t/10294165.
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using std::__math::__ucrt::isfinite;
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using std::__math::__ucrt::isgreater;
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using std::__math::__ucrt::isgreaterequal;
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using std::__math::__ucrt::isinf;
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using std::__math::__ucrt::isless;
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using std::__math::__ucrt::islessequal;
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using std::__math::__ucrt::islessgreater;
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using std::__math::__ucrt::isnan;
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using std::__math::__ucrt::isnormal;
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using std::__math::__ucrt::isunordered;
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# endif // defined(_LIBCPP_MSVCRT) && _LIBCPP_STD_VER >= 20
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// We have to provide double overloads for <math.h> to work on platforms that don't provide the full set of math
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// functions. To make the overload set work with multiple functions that take the same arguments, we make our overloads
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// templates. Functions are preferred over function templates during overload resolution, which means that our overload

‎libcxx/test/libcxx/fuzzing/random.pass.cpp

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//
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//===----------------------------------------------------------------------===//
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// This doesn't work on Windows because in the MSVC UCRT headers the math.h is
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// actually intended to implement the full C++ spec requirements. For details
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// see https://github.com/llvm/llvm-project/issues/70225#issuecomment-1992528828
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// XFAIL: msvc
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// UNSUPPORTED: c++03, c++11
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#include <cassert>

‎libcxx/test/std/depr/depr.c.headers/math_h.pass.cpp

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//
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//===----------------------------------------------------------------------===//
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// This doesn't work on Windows because in the MSVC UCRT headers the math.h is
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// actually intended to implement the full C++ spec requirements. For details
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// see https://github.com/llvm/llvm-project/issues/70225#issuecomment-1992528828
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// XFAIL: msvc
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// <math.h>
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// GCC warns about signbit comparing `bool_v < 0`, which we're testing

‎libcxx/test/std/numerics/c.math/cmath.pass.cpp

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//
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//===----------------------------------------------------------------------===//
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// This doesn't work on Windows because in the MSVC UCRT headers the math.h is
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// actually intended to implement the full C++ spec requirements. For details
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// see https://github.com/llvm/llvm-project/issues/70225#issuecomment-1992528828
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// XFAIL: msvc
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// <cmath>
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#include <cmath>

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