Initial version

src/include/units/bits/tools.h

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+// 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 <ratio>
+#include <type_traits>
+
+namespace mp {
+
+  // Requires
+
+  template<bool B>
+  using Requires = std::enable_if_t<B, bool>;
+
+  // static_sign
+
+  template<std::intmax_t Pn>
+  struct static_sign : std::integral_constant<std::intmax_t, (Pn < 0) ? -1 : 1> {
+  };
+
+  // static_abs
+
+  template<std::intmax_t Pn>
+  struct static_abs : std::integral_constant<std::intmax_t, Pn * static_sign<Pn>::value> {
+  };
+
+  // static_gcd
+
+  template<std::intmax_t Pn, std::intmax_t Qn>
+  struct static_gcd : static_gcd<Qn, (Pn % Qn)> {
+  };
+
+  template<std::intmax_t Pn>
+  struct static_gcd<Pn, 0> : std::integral_constant<std::intmax_t, static_abs<Pn>::value> {
+  };
+
+  template<std::intmax_t Qn>
+  struct static_gcd<0, Qn> : std::integral_constant<std::intmax_t, static_abs<Qn>::value> {
+  };
+
+  // is_ratio
+
+  template<typename T>
+  struct is_ratio : std::false_type {
+  };
+
+  template<intmax_t Num, intmax_t Den>
+  struct is_ratio<std::ratio<Num, Den>> : std::true_type {
+  };
+
+  // common_ratio
+
+  // todo: simplified
+  template<typename Ratio1, typename Ratio2>
+  struct common_ratio {
+    using gcd_num = static_gcd<Ratio1::num, Ratio2::num>;
+    using gcd_den = static_gcd<Ratio1::den, Ratio2::den>;
+    using type = std::ratio<gcd_num::value, (Ratio1::den / gcd_den::value) * Ratio2::den>;
+  };
+
+  template<typename Ratio1, typename Ratio2>
+  using common_ratio_t = typename common_ratio<Ratio1, Ratio2>::type;
+
+}  // namespace mp