Add dot product

src/quaternion.rs

@@ -33,6 +33,8 @@ pub trait Quaternion<T> {
     pure fn sub_q(other: &self) -> self;
     pure fn mul_q(other: &self) -> self;
     
+    pure fn dot(other: &self) -> T;
+    
     pure fn conjugate() -> self;
     pure fn inverse() -> self;
     pure fn length2() -> T;
@@ -122,6 +124,14 @@ pub impl<T:Copy Num NumCast Exp FuzzyEq> Quat<T>: Quaternion<T> {
                   self.w * other.z + self.z * other.w + self.x * other.y - self.y * other.x) 
     }
     
+    #[inline(always)]
+    pure fn dot(other: &Quat<T>) -> T {
+        self.w * other.w +
+        self.x * other.x +
+        self.y * other.y +
+        self.z * other.z
+    }
+    
     #[inline(always)]
     pure fn conjugate() -> Quat<T> {
         Quat::new(self.w, -self.x, -self.y, -self.z)