[libcxx-commits] [libcxx] [libc++][math] Add `constexpr` for `std::signbit()` (PR #105946)

[Robin Caloudis via libcxx-commits]

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@@ -0,0 +1,83 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// bool signbit(floating-point-type x); // constexpr since C++23
+
+// We don't control the implementation on windows
+// UNSUPPORTED: windows
+
+// These compilers don't support constexpr `__builtin_signbit` yet.
+// UNSUPPORTED: clang-17, clang-18, clang-19, apple-clang-16, apple-clang-17
+
+#include <cassert>
+#include <cmath>
+#include <limits>
+
+#include "test_macros.h"
+#include "type_algorithms.h"
+
+struct TestFloat {
+  template <class T>
+  static TEST_CONSTEXPR_CXX23 bool test() {
+    assert(!std::signbit(T(0)));
+    assert(!std::signbit(std::numeric_limits<T>::min()));
+    assert(!std::signbit(std::numeric_limits<T>::denorm_min()));
+    assert(!std::signbit(std::numeric_limits<T>::max()));
+    assert(!std::signbit(std::numeric_limits<T>::infinity()));
+    assert(!std::signbit(std::numeric_limits<T>::quiet_NaN()));
+    assert(!std::signbit(std::numeric_limits<T>::signaling_NaN()));
+    assert(std::signbit(-T(0)));
+    assert(std::signbit(-std::numeric_limits<T>::infinity()));
+    assert(std::signbit(std::numeric_limits<T>::lowest()));
+
+    return true;
+  }
+
+  template <class T>
+  TEST_CONSTEXPR_CXX23 void operator()() {
+    test<T>();
+#if TEST_STD_VER >= 23
+    static_assert(test<T>());
+#endif
+  }
+};
+
+struct TestInt {
+  template <class T>
+  static TEST_CONSTEXPR_CXX23 bool test() {
+    assert(!std::signbit(std::numeric_limits<T>::max()));
+    assert(!std::signbit(T(0)));
+    if (std::is_unsigned<T>::value) {
+      assert(!std::signbit(std::numeric_limits<T>::lowest()));
+    } else {
+      assert(std::signbit(std::numeric_limits<T>::lowest()));
+    }
+
+    return true;
+  }
+
+  template <class T>
+  TEST_CONSTEXPR_CXX23 void operator()() {
+    test<T>();
+#if TEST_STD_VER >= 23
+    static_assert(test<T>());
+#endif
+  }
+};
+
+template <typename T>
+struct ConvertibleTo {
+  operator T() const { return T(); }
+};
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robincaloudis wrote:

Good catch! Done.

https://github.com/llvm/llvm-project/pull/105946