Support negative exponent in power_of_unit (#227)

* Update units.h * Update main.cpp * fix typo Co-authored-by: Nic Holthaus <[email protected]>
nholthaus · Oct 10, 2020 · ea6d126 · ea6d126
1 parent 1e2c7ed
commit ea6d126
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Showing 2 changed files with 32 additions and 1 deletion.
diff --git a/include/units.h b/include/units.h
@@ -2756,14 +2756,30 @@ namespace units
 		/// recursive exponential implementation
 		template <int N, class U> struct power_of_unit
 		{
-			typedef typename units::detail::unit_multiply<U, typename power_of_unit<N - 1, U>::type> type;
+			template<bool isPos, int V> struct power_of_unit_impl;
+
+			template<int V> struct power_of_unit_impl<true, V>
+			{
+				typedef units::detail::unit_multiply<U, typename power_of_unit<N - 1, U>::type> type;
+			};
+
+			template<int V> struct power_of_unit_impl<false, V>
+			{
+				typedef units::inverse<typename power_of_unit<-N, U>::type> type;
+			};
+
+			typedef typename power_of_unit_impl<(N > 0), N>::type type;
 		};
 
 		/// End recursion
 		template <class U> struct power_of_unit<1, U>
 		{
 			typedef U type;
 		};
+		template <class U> struct power_of_unit<0, U>
+		{
+			typedef units::dimensionless::dimensionless type;
+		};
 	}
 	/** @endcond */	// END DOXYGEN IGNORE
 

diff --git a/unitTests/main.cpp b/unitTests/main.cpp
@@ -2817,6 +2817,21 @@ TEST_F(UnitMath, pow)
 	bool isSame;
 	meter_t value(10.0);
 
+	auto inv_sq = pow<-2>(value);
+	EXPECT_NEAR(0.01, inv_sq(), 5.0e-5);
+	isSame = std::is_same<decltype(inv_sq), unit_t<inverse<square_meter>>>::value;
+	EXPECT_TRUE(isSame);
+
+	auto inv = pow<-1>(value);
+	EXPECT_NEAR(0.1, inv(), 5.0e-4);
+	isSame = std::is_same<decltype(inv), unit_t<inverse<meter>>>::value;
+	EXPECT_TRUE(isSame);
+
+	auto scalar = pow<0>(value);
+	EXPECT_NEAR(1, scalar(), 5.0e-3);
+	isSame = std::is_same<decltype(scalar), scalar_t>::value;
+	EXPECT_TRUE(isSame);
+
 	auto sq = pow<2>(value);
 	EXPECT_NEAR(100.0, sq(), 5.0e-2);
 	isSame = std::is_same<decltype(sq), square_meter_t>::value;