Add Mul implementation

Author: daalfox

src/source/amplify.rs

@@ -23,16 +23,28 @@ impl From<AmpFactor> for f32 {
     }
 }
 
-#[inline]
 fn decibels_to_linear(decibels: f32) -> f32 {
     f32::powf(10.0f32, decibels / 20.0)
 }
 
+fn linear_to_decibels(linear: f32) -> f32 {
+    20.0 * f32::log10(linear.abs())
+}
+
 impl Mul for AmpFactor {
     type Output = Self;
 
     fn mul(self, rhs: Self) -> Self::Output {
-        todo!()
+        match self {
+            AmpFactor::Linear(l1) => match rhs {
+                AmpFactor::Linear(l2) => Self::Linear(l1 * l2),
+                AmpFactor::Decibel(d2) => Self::Linear(l1 * decibels_to_linear(d2)),
+            },
+            AmpFactor::Decibel(d1) => match rhs {
+                AmpFactor::Linear(l2) => AmpFactor::Decibel(d1 * linear_to_decibels(l2)),
+                AmpFactor::Decibel(d2) => AmpFactor::Decibel(d1 * d2),
+            },
+        }
     }
 }