From bce17a8476b9c42468aa25765cfc2af29f81026a Mon Sep 17 00:00:00 2001
From: Mateusz Pusz <mateusz.pusz@gmail.com>
Date: Tue, 10 Sep 2019 21:20:32 +0200
Subject: [PATCH] Fractional dimension exponents support added

---
 src/include/units/dimension.h        | 30 ++++++++-----
 src/include/units/unit.h             | 16 +++----
 test/unit_test/CMakeLists.txt        |  1 +
 test/unit_test/test_custom_units.cpp | 64 ++++++++++++++++++++++++++++
 test/unit_test/test_dimension.cpp    |  3 ++
 5 files changed, 95 insertions(+), 19 deletions(-)
 create mode 100644 test/unit_test/test_custom_units.cpp

diff --git a/src/include/units/dimension.h b/src/include/units/dimension.h
index 47039cae..d78f8177 100644
--- a/src/include/units/dimension.h
+++ b/src/include/units/dimension.h
@@ -24,6 +24,8 @@
 
 #include <units/bits/type_list.h>
 #include <units/bits/downcasting.h>
+#include <units/ratio.h>
+#include <ratio>
 
 namespace std::experimental::units {
 
@@ -60,10 +62,11 @@ namespace std::experimental::units {
 
   // exp
 
-  template<const base_dimension& BaseDimension, int Value>
+  template<const base_dimension& BaseDimension, int Num, int Den = 1>
   struct exp {
     static constexpr const base_dimension& dimension = BaseDimension;
-    static constexpr int value = Value;
+    static constexpr int num = Num;
+    static constexpr int den = Den;
   };
 
   // is_exp
@@ -71,8 +74,8 @@ namespace std::experimental::units {
     template<typename T>
     inline constexpr bool is_exp = false;
 
-    template<const base_dimension& BaseDimension, int Value>
-    inline constexpr bool is_exp<exp<BaseDimension, Value>> = true;
+    template<const base_dimension& BaseDimension, int Num, int Den>
+    inline constexpr bool is_exp<exp<BaseDimension, Num, Den>> = true;
   }  // namespace detail
 
   template<typename T>
@@ -89,9 +92,9 @@ namespace std::experimental::units {
   template<Exponent E>
   struct exp_invert;
 
-  template<const base_dimension& BaseDimension, int Value>
-  struct exp_invert<exp<BaseDimension, Value>> {
-    using type = exp<BaseDimension, -Value>;
+  template<const base_dimension& BaseDimension, int Num, int Den>
+  struct exp_invert<exp<BaseDimension, Num, Den>> {
+    using type = exp<BaseDimension, -Num, Den>;
   };
 
   template<Exponent E>
@@ -131,6 +134,7 @@ namespace std::experimental::units {
   using dim_invert_t = dim_invert<typename D::base_type>::type;
 
 
+  // todo: force as the only user interface to create dimensions through modules
   // make_dimension
 
   namespace detail {
@@ -157,10 +161,14 @@ namespace std::experimental::units {
       using type = conditional<std::is_same_v<rest, dimension<>>, dimension<E1>, type_list_push_front<rest, E1>>;
     };
 
-    template<const base_dimension& D, int V1, int V2, typename... ERest>
-    struct dim_consolidate<dimension<exp<D, V1>, exp<D, V2>, ERest...>> {
-      using type = conditional<V1 + V2 == 0, dim_consolidate_t<dimension<ERest...>>,
-                               dim_consolidate_t<dimension<exp<D, V1 + V2>, ERest...>>>;
+    template<const base_dimension& D, int Num1, int Den1, int Num2, int Den2, typename... ERest>
+    struct dim_consolidate<dimension<exp<D, Num1, Den1>, exp<D, Num2, Den2>, ERest...>> {
+      // todo: provide custom implementation for ratio_add
+      using r1 = std::ratio<Num1, Den1>;
+      using r2 = std::ratio<Num2, Den2>;
+      using r = std::ratio_add<r1, r2>;
+      using type = conditional<r::num == 0, dim_consolidate_t<dimension<ERest...>>,
+                               dim_consolidate_t<dimension<exp<D, r::num, r::den>, ERest...>>>;
     };
 
   }  // namespace detail
diff --git a/src/include/units/unit.h b/src/include/units/unit.h
index c9ccb3d5..15e69e61 100644
--- a/src/include/units/unit.h
+++ b/src/include/units/unit.h
@@ -78,20 +78,20 @@ namespace std::experimental::units {
                                 typename get_ratio<BaseDimension, Rest...>::ratio>;
     };
 
-    template<typename Result, int UnitExpValue, typename UnitRatio>
+    template<typename Result, int UnitExpNum, int UnitExpDen, typename UnitRatio>
     struct ratio_op;
 
-    template<typename Result, typename UnitRatio>
-    struct ratio_op<Result, 0, UnitRatio> {
+    template<typename Result, int UnitExpDen, typename UnitRatio>
+    struct ratio_op<Result, 0, UnitExpDen, UnitRatio> {
       using ratio = Result;
     };
 
-    template<typename Result, int UnitExpValue, typename UnitRatio>
+    template<typename Result, int UnitExpNum, int UnitExpDen, typename UnitRatio>
     struct ratio_op {
-      using calc_ratio = conditional<(UnitExpValue > 0), ratio_multiply<Result, UnitRatio>,
+      using calc_ratio = conditional<(UnitExpNum * UnitExpDen > 0), ratio_multiply<Result, UnitRatio>,
                                      ratio_divide<Result, UnitRatio>>;
-      static constexpr int value = UnitExpValue > 0 ? UnitExpValue - 1 : UnitExpValue + 1;
-      using ratio = ratio_op<calc_ratio, value, UnitRatio>::ratio;
+      static constexpr int value = (UnitExpNum * UnitExpDen > 0) ? (UnitExpNum - UnitExpDen) : (UnitExpNum + UnitExpDen);
+      using ratio = ratio_op<calc_ratio, value, UnitExpDen, UnitRatio>::ratio;
     };
 
     template<typename D, typename... Us>
@@ -106,7 +106,7 @@ namespace std::experimental::units {
     struct derived_ratio<dimension<E, Rest...>, Us...> {
       using rest_ratio = derived_ratio<dimension<Rest...>, Us...>::ratio;
       using e_ratio = get_ratio<E::dimension, Us...>::ratio;
-      using ratio = ratio_op<rest_ratio, E::value, e_ratio>::ratio;
+      using ratio = ratio_op<rest_ratio, E::num, E::den, e_ratio>::ratio;
     };
 
   }
diff --git a/test/unit_test/CMakeLists.txt b/test/unit_test/CMakeLists.txt
index 9637450e..cbb5f987 100644
--- a/test/unit_test/CMakeLists.txt
+++ b/test/unit_test/CMakeLists.txt
@@ -22,6 +22,7 @@
 
 # unit tests
 add_library(unit_tests
+    test_custom_units.cpp
     test_dimension.cpp
     test_quantity.cpp
     test_tools.cpp
diff --git a/test/unit_test/test_custom_units.cpp b/test/unit_test/test_custom_units.cpp
new file mode 100644
index 00000000..a7c8c77b
--- /dev/null
+++ b/test/unit_test/test_custom_units.cpp
@@ -0,0 +1,64 @@
+// 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.
+
+#include <units/dimensions/voltage.h>
+
+
+/* ************** DERIVED DIMENSIONS THAT INCLUDE UNITS WITH SPECIAL NAMES **************** */
+
+namespace {
+
+using namespace std::experimental::units;
+
+  // power spectral density
+  // todo: add support for make_dimension_t of non base units
+  //  struct power_spectral_density : make_dimension_t<exp<voltage, 2>, exp<frequency, -1>> {};
+  struct power_spectral_density
+      : make_dimension_t<exp<base_dim_mass, 2>, exp<base_dim_length, 4>, exp<base_dim_time, -6>, exp<base_dim_time, -1>> {
+  };
+  struct sq_volt_per_hertz : unit<power_spectral_density> {};
+
+  // amplitude spectral density
+  //  struct dimension_amplitude_spectral_density : make_dimension_t<exp<voltage, 1>, exp<frequency, -1, 2>> {};
+  struct amplitude_spectral_density
+      : make_dimension_t<exp<base_dim_mass, 1>, exp<base_dim_length, 2>, exp<base_dim_time, -3>, exp<base_dim_current, -1>, exp<base_dim_time, 1, 2>> {
+  };
+  // todo: add support for derived_unit
+  //struct volt_per_sq_hertz : derived_unit<amplitude_spectral_density, kilogram, metre, second, ampere > {};
+  struct volt_per_sqrt_hertz : unit<amplitude_spectral_density> {};
+}
+
+namespace std::experimental::units {
+
+template<> struct downcasting_traits<downcast_from<power_spectral_density>> : downcast_to<power_spectral_density> {};
+template<> struct downcasting_traits<downcast_from<sq_volt_per_hertz>> : downcast_to<sq_volt_per_hertz> {};
+
+template<> struct downcasting_traits<downcast_from<amplitude_spectral_density>> : downcast_to<amplitude_spectral_density> {};
+template<> struct downcasting_traits<downcast_from<volt_per_sqrt_hertz>> : downcast_to<volt_per_sqrt_hertz> {};
+
+}
+
+namespace {
+
+  //static_assert(sqrt(quantity<sq_volt_per_hertz>(4)) = quantity<volt_per_sqrt_hertz>(2));
+
+}
diff --git a/test/unit_test/test_dimension.cpp b/test/unit_test/test_dimension.cpp
index 8f4bb9bb..182c54b5 100644
--- a/test/unit_test/test_dimension.cpp
+++ b/test/unit_test/test_dimension.cpp
@@ -44,6 +44,9 @@ namespace {
   static_assert(std::is_same_v<make_dimension_t<exp<d1, 1>, exp<d0, 1>>, dimension<exp<d0, 1>, exp<d1, 1>>>);
   static_assert(std::is_same_v<make_dimension_t<exp<d1, 1>, exp<d1, 1>>, dimension<exp<d1, 2>>>);
   static_assert(std::is_same_v<make_dimension_t<exp<d1, 1>, exp<d1, -1>>, dimension<>>);
+  static_assert(std::is_same_v<make_dimension_t<exp<d1, 1>, exp<d1, 1, 2>>, dimension<exp<d1, 3, 2>>>);
+  static_assert(std::is_same_v<make_dimension_t<exp<d1, 1, 2>, exp<d1, 1, 2>>, dimension<exp<d1, 1>>>);
+  static_assert(std::is_same_v<make_dimension_t<exp<d1, 2>, exp<d1, 1, 2>>, dimension<exp<d1, 5, 2>>>);
 
   static_assert(std::is_same_v<make_dimension_t<exp<d0, 1>, exp<d1, 1>, exp<d0, 1>, exp<d1, 1>>, dimension<exp<d0, 2>, exp<d1, 2>>>);
   static_assert(