Impl multiplication and division for frequency wrappers (#193)

This allows the following operations:

- T * u32 (T)
- T *= u32 (T)
- T / u32 (T)
- T /= u32 (T)
- T / T (u32)

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Extend the Pwm implementation to cover the full embedded_hal::Pwm API
 - Add `QeiOptions` struct to configure slave mode and auto reload value of QEI interface
+- Implement multiplication and division for frequency wrappers (#193)
 
 ### Changed
 

src/time.rs

@@ -27,6 +27,7 @@
 //! assert_eq!(freq_khz, freq_mhz);
 //! ```
 
+use core::ops;
 use cortex_m::peripheral::DWT;
 
 use crate::rcc::Clocks;
@@ -181,6 +182,50 @@ impl Into<Hertz> for MicroSeconds {
     }
 }
 
+/// Macro to implement arithmetic operations (e.g. multiplication, division)
+/// for wrapper types.
+macro_rules! impl_arithmetic {
+    ($wrapper:ty, $wrapped:ty) => {
+        impl ops::Mul<$wrapped> for $wrapper {
+            type Output = Self;
+            fn mul(self, rhs: $wrapped) -> Self {
+                Self(self.0 * rhs)
+            }
+        }
+
+        impl ops::MulAssign<$wrapped> for $wrapper {
+            fn mul_assign(&mut self, rhs: $wrapped) {
+                self.0 *= rhs;
+            }
+        }
+
+        impl ops::Div<$wrapped> for $wrapper {
+            type Output = Self;
+            fn div(self, rhs: $wrapped) -> Self {
+                Self(self.0 / rhs)
+            }
+        }
+
+        impl ops::Div<$wrapper> for $wrapper {
+            type Output = $wrapped;
+            fn div(self, rhs: $wrapper) -> $wrapped {
+                self.0 / rhs.0
+            }
+        }
+
+        impl ops::DivAssign<$wrapped> for $wrapper {
+            fn div_assign(&mut self, rhs: $wrapped) {
+                self.0 /= rhs;
+            }
+        }
+    }
+}
+
+impl_arithmetic!(Hertz, u32);
+impl_arithmetic!(KiloHertz, u32);
+impl_arithmetic!(MegaHertz, u32);
+impl_arithmetic!(Bps, u32);
+
 /// A monotonic non-decreasing timer
 #[derive(Clone, Copy)]
 pub struct MonoTimer {