feat: compare.h header added with checks against zero

Resolves #487

src/utility/include/mp-units/compare.h

@@ -0,0 +1,95 @@
+// The MIT License (MIT)
+//
+// Copyright (c) 2018 Mateusz Pusz
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+#pragma once
+
+#include <compare>
+
+namespace mp_units {
+
+template<typename T>
+  requires requires {
+    {
+      T::zero()
+    } -> std::equality_comparable_with<T>;
+  }
+[[nodiscard]] constexpr bool is_eq_zero(T v)
+{
+  return v == T::zero();
+}
+
+template<typename T>
+  requires requires {
+    {
+      T::zero()
+    } -> std::equality_comparable_with<T>;
+  }
+[[nodiscard]] constexpr bool is_neq_zero(T v)
+{
+  return v != T::zero();
+}
+
+template<typename T>
+  requires requires {
+    {
+      T::zero()
+    } -> std::three_way_comparable_with<T>;
+  }
+[[nodiscard]] constexpr bool is_lt_zero(T v)
+{
+  return v < T::zero();
+}
+
+template<typename T>
+  requires requires {
+    {
+      T::zero()
+    } -> std::three_way_comparable_with<T>;
+  }
+[[nodiscard]] constexpr bool is_gt_zero(T v)
+{
+  return v > T::zero();
+}
+
+template<typename T>
+  requires requires {
+    {
+      T::zero()
+    } -> std::three_way_comparable_with<T>;
+  }
+[[nodiscard]] constexpr bool is_lteq_zero(T v)
+{
+  return v <= T::zero();
+}
+
+template<typename T>
+  requires requires {
+    {
+      T::zero()
+    } -> std::three_way_comparable_with<T>;
+  }
+[[nodiscard]] constexpr bool is_gteq_zero(T v)
+{
+  return v >= T::zero();
+}
+
+}  // namespace mp_units