[libcxx-commits] [libcxx] [libc++][math] Add `constexpr` to comparison functions (PR #210075)

[A. Jiang via libcxx-commits]

================
@@ -0,0 +1,92 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 isgreater(floating-point-type x, floating-point-type y); // constexpr since C++23
+
+#include <cassert>
+#include <cmath>
+#include <limits>
+#include <type_traits>
+
+#include "test_macros.h"
+#include "type_algorithms.h"
+
+struct TestFloat {
+  template <class T>
+  static TEST_CONSTEXPR_CXX23 bool test() {
+    assert(std::isgreater(std::numeric_limits<T>::max(), T(0)));
+    assert(!std::isgreater(T(0), std::numeric_limits<T>::max()));
+    assert(!std::isgreater(std::numeric_limits<T>::max(), std::numeric_limits<T>::max()));
+
+    assert(std::isgreater(std::numeric_limits<T>::infinity(), std::numeric_limits<T>::max()));
+    assert(!std::isgreater(-std::numeric_limits<T>::infinity(), std::numeric_limits<T>::lowest()));
+    assert(!std::isgreater(std::numeric_limits<T>::infinity(), std::numeric_limits<T>::infinity()));
+
+    assert(!std::isgreater(std::numeric_limits<T>::quiet_NaN(), T(0)));
+    assert(!std::isgreater(T(0), std::numeric_limits<T>::quiet_NaN()));
+    assert(!std::isgreater(std::numeric_limits<T>::quiet_NaN(), std::numeric_limits<T>::quiet_NaN()));
+    assert(!std::isgreater(std::numeric_limits<T>::signaling_NaN(), T(0)));
+
+    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::isgreater(std::numeric_limits<T>::max(), T(0)));
+    assert(!std::isgreater(T(0), std::numeric_limits<T>::max()));
+    assert(!std::isgreater(std::numeric_limits<T>::max(), std::numeric_limits<T>::max()));
+
+    assert(!std::isgreater(T(1), T(1)));
+    assert(!std::isgreater(std::numeric_limits<T>::lowest(), T(0)));
+
+    if (std::is_signed<T>::value) {
+      assert(std::isgreater(T(-1), std::numeric_limits<T>::lowest()));
+      assert(!std::isgreater(std::numeric_limits<T>::lowest(), T(-1)));
+    }
+
+    return true;
+  }
+
+  template <class T>
+  TEST_CONSTEXPR_CXX23 void operator()() {
+    test<T>();
+#if TEST_STD_VER >= 23
+    static_assert(test<T>());
+#endif
+  }
----------------
frederick-vs-ja wrote:

> I copied the exact same assertion behaviour from `signbit.pass.cpp` which is part of the PR of `constexpr` for `std::signbit`.

I don't think it's a good idea to be consistent with an old, inconsistent test. Let's refactor these into:
```c++
TEST_CONSTEXPR_CXX23 bool test() {
  // ...
  return true;
}

int main(int, char**) {
  test();
#if TEST_STD_VER >= 23
  static_assert(test());
#endif
}
```

I think it would be better to open another PR to refactor the test for `signbit`.

https://github.com/llvm/llvm-project/pull/210075