[libc++][math] Provide overloads for cv-unqualified floating point types for std::isnormal

[robincaloudis]

Why

Currently, the following does not work when compiled with clang:

#include <cmath>

struct ConvertibleToFloat {
    operator float();
};

bool test(ConvertibleToFloat x) {
    return std::isnormal(x);
}

See https://godbolt.org/z/5bos8v67T for differences with respect to msvc, gcc or icx. It fails for float, double and long double (all cv-unqualified floating-point types).

What

Test and provide overloads as expected by the ISO C++ standard. The classification/comparison function isnormal is defined since C++11 until C++23 as

bool isnormal( float num );
bool isnormal( double num );
bool isnormal( long double num );

and since C++23 as

constexpr bool isnormal( /* floating-point-type */ num );

for which "the library provides overloads for all cv-unqualified floating-point types as the type of the parameter num". See §28.7.1/1 in the ISO C++ standard or check cppreference.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Robin Caloudis (robincaloudis)

Changes

Why

Currently, the following does not work when compiled with clang:

#include <cmath>

struct ConvertibleToFloat {
    operator float();
};

bool test(ConvertibleToFloat x) {
    return std::isnormal(x);
}

See https://godbolt.org/z/5bos8v67T for differences with respect to msvc, gcc or icx. If fails for double and long double as well. As the classification/comparison function isnormal is defined since C++11 until C++23 as

bool isnormal( float num );
bool isnormal( double num );
bool isnormal( long double num );

and since C++23 as

constexpr bool isnormal( /* floating-point-type */ num );

for which "the library provides overloads for all cv-unqualified floating-point types as the type of the parameter num", it is actually expected that convertibles types work due to the present of the overloads for all cv-unqualified floating point types. See §28.7.1/1 in the ISO C++ standard or check cppreference.

What

Test and provide overloads as expected by the ISO C++ standard.

---

Full diff: https://github.com/llvm/llvm-project/pull/104773.diff

2 Files Affected:

• (modified) libcxx/include/__math/traits.h (+12)
• (modified) libcxx/test/std/numerics/c.math/isnormal.pass.cpp (+14)

diff --git a/libcxx/include/__math/traits.h b/libcxx/include/__math/traits.h
index 35c283cc9e21ce..9fe1de66a80985 100644
--- a/libcxx/include/__math/traits.h
+++ b/libcxx/include/__math/traits.h
@@ -137,6 +137,18 @@ _LIBCPP_NODISCARD _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnor
   return __x != 0;
 }
 
+_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(float __x) _NOEXCEPT {
+  return __builtin_isnormal(__x);
+}
+
+_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(double __x) _NOEXCEPT {
+  return __builtin_isnormal(__x);
+}
+
+_LIBCPP_NODISCARD inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool isnormal(long double __x) _NOEXCEPT {
+  return __builtin_isnormal(__x);
+}
+
 // isgreater
 
 template <class _A1, class _A2, __enable_if_t<is_arithmetic<_A1>::value && is_arithmetic<_A2>::value, int> = 0>
diff --git a/libcxx/test/std/numerics/c.math/isnormal.pass.cpp b/libcxx/test/std/numerics/c.math/isnormal.pass.cpp
index c3b8f31359f988..76c3d13520d996 100644
--- a/libcxx/test/std/numerics/c.math/isnormal.pass.cpp
+++ b/libcxx/test/std/numerics/c.math/isnormal.pass.cpp
@@ -62,9 +62,23 @@ struct TestInt {
   }
 };
 
+template <typename T>
+struct ConvertibleTo {
+  operator T() const { return T(1); }
+};
+
 int main(int, char**) {
   types::for_each(types::floating_point_types(), TestFloat());
   types::for_each(types::integral_types(), TestInt());
 
+  // Make sure we can call `std::isnormal` with convertible types. This checks
+  // whether overloads for all cv-unqualified floating-point types are working
+  // as expected.
+  {
+    assert(std::isnormal(ConvertibleTo<float>()));
+    assert(std::isnormal(ConvertibleTo<double>()));
+    assert(std::isnormal(ConvertibleTo<long double>()));
+  }
+
   return 0;
 }

[philnik777]

The is_floating_point constrained overload is now unused, right? In that case it should be removed.

[robincaloudis]

Absolutely. You are right. Corrected it. In addition, I opened #106224 that removes the constrained overloads for std::{isinf,isfinite,isnan} too. Feel free to review both.