Add fma to math.h

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

@@ -136,6 +136,37 @@ template<auto R, typename Rep>
   return {static_cast<Rep>(abs(q.numerical_value_ref_in(q.unit))), R};
 }
 
+/**
+ * @brief Computes the fma of 3 quantities
+ *
+ * @param a: Multiplicand
+ * @param x: Multiplicand
+ * @param b: Addend
+ * @return Quantity: The nearest floating point representable to ax+b
+ */
+template<auto R, auto S, auto T, typename Rep1, typename Rep2, typename Rep3>
+[[nodiscard]] constexpr QuantityOf<common_quantity_spec(get_quantity_spec(R) * get_quantity_spec(S),
+                                                        get_quantity_spec(T))> auto
+fma(const quantity<R, Rep1>& a, const quantity<S, Rep2>& x, const quantity<T, Rep3>& b) noexcept
+  requires requires { common_quantity_spec(get_quantity_spec(R) * get_quantity_spec(S), get_quantity_spec(T)); } &&
+           (get_unit(R) * get_unit(S) == get_unit(T)) &&
+           (
+             requires {
+               fma(a.numerical_value_ref_in(a.unit), x.numerical_value_ref_in(x.unit),
+                   b.numerical_value_ref_in(b.unit));
+             } ||
+             requires {
+               std::fma(a.numerical_value_ref_in(a.unit), x.numerical_value_ref_in(x.unit),
+                        b.numerical_value_ref_in(b.unit));
+             })
+{
+  using std::fma;
+  return quantity{
+    fma(a.numerical_value_ref_in(a.unit), x.numerical_value_ref_in(x.unit), b.numerical_value_ref_in(b.unit)),
+    common_reference(R * S, T)};
+}
+
+
 /**
  * @brief Returns the epsilon of the quantity
  *

test/unit_test/runtime/math_test.cpp

@@ -62,6 +62,17 @@ TEST_CASE("'cbrt()' on quantity changes the value and the dimension accordingly"
   REQUIRE(cbrt(8 * isq::volume[m3]) == 2 * isq::length[m]);
 }
 
+TEST_CASE("'fma()' on quantity changes the value and the dimension accordingly", "[math][fma]")
+{
+  REQUIRE(fma(1.0 * isq::length[m], 2.0 * one, 2.0 * isq::length[m]) == 4.0 * isq::length[m]);
+}
+
+TEST_CASE("'fma()' returns a common reference.", "[math][fma]")
+{
+  REQUIRE(fma(isq::speed(10.0 * m / s), isq::time(2.0 * s), isq::height(42.0 * m)) == isq::length(62.0 * m));
+}
+
+
 TEST_CASE("'pow<Num, Den>()' on quantity changes the value and the dimension accordingly", "[math][pow]")
 {
   REQUIRE(pow<1, 4>(16 * isq::area[m2]) == sqrt(4 * isq::length[m]));

test/unit_test/static/math_test.cpp

@@ -40,6 +40,10 @@ template<typename T1, typename T2, typename... Ts>
 
 #if __cpp_lib_constexpr_cmath || MP_UNITS_COMP_GCC
 
+static_assert(compare(fma(2.0 * s, 3.0 * Hz, 1.0 * one), 7.0 * one));
+static_assert(compare(fma(2.0 * one, 3.0 * m, 1.0 * m), 7.0 * m));
+static_assert(compare(fma(2.0 * m, 3.0 * one, 1.0 * m), 7.0 * m));
+static_assert(compare(fma(2 * m, 3.0f * m, 1.0 * m2), 7.0 * m2));
 static_assert(compare(pow<0>(2 * m), 1 * one));
 static_assert(compare(pow<1>(2 * m), 2 * m));
 static_assert(compare(pow<2>(2 * m), 4 * pow<2>(m), 4 * m2));