Implement floating point powi method.

Part of #11.
iliekturtles · Jun 18, 2017 · efdc9de · efdc9de
1 parent c40097e
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -21,6 +21,8 @@
    `max` and `min` for `Quantity`.
  * [#11](https://github.com/iliekturtles/uom/issues/11) Add floating point `mul_add` method for
    `Quantity`.
+ * [#11](https://github.com/iliekturtles/uom/issues/11) Add floating point `powi` method for
+   `Quantity`.
 
 ## [v0.14.0] — 2017-05-30
 

diff --git a/src/system.rs b/src/system.rs
@@ -587,6 +587,31 @@ macro_rules! system {
                         }
                     }
 
+                    /// Raises a quantity to an integer power.
+                    ///
+                    /// ```
+                    #[cfg_attr(feature = "f32", doc = " # use uom::si::f32::*;")]
+                    #[cfg_attr(not(feature = "f32"), doc = " # use uom::si::f64::*;")]
+                    /// # use uom::si::length::meter;
+                    /// let a: Area = Length::new::<meter>(3.0).powi(::uom::typenum::P2::new());
+                    /// ```
+                    #[cfg(feature = "std")]
+                    #[inline(always)]
+                    pub fn powi<E>(self, _e: E) -> Quantity<$crate::typenum::Prod<D, DN<E>>, U, $V>
+                    where
+                        D: $crate::stdlib::ops::Mul<DN<E>>,
+                        U: Units<$crate::typenum::Prod<D, DN<E>>, $V>,
+                        E: $crate::typenum::Integer,
+                        $crate::typenum::Prod<D, DN<E>>: Dimension,
+                    {
+                        Quantity {
+                            dimension: $crate::stdlib::marker::PhantomData,
+                            units: $crate::stdlib::marker::PhantomData,
+                            // TODO #29 value: self.value.powi(e), // if $V becomes V.
+                            value: self.value.powi(E::to_i32()),
+                        }
+                    }
+
                     /// Takes the square root of a number. Returns `NaN` if `self` is a negative
                     /// number.
                     ///

diff --git a/src/tests.rs b/src/tests.rs
@@ -365,6 +365,14 @@ macro_rules! test {
                 }
             }
 
+            quickcheck! {
+                #[cfg(feature = "std")]
+                #[allow(trivial_casts)]
+                fn powi(v: $V) -> bool {
+                    v.powi(3) == TLength::new::<meter>(v).powi(P3::new()).value
+                }
+            }
+
             quickcheck! {
                 #[cfg(feature = "std")]
                 #[allow(trivial_casts)]