quaternion: improve comments

matrix/Quaternion.hpp

@@ -195,9 +195,10 @@ class Quaternion : public Vector<Type, 4>
         Quaternion &q = *this;
         Vector3<Type> cr = src.cross(dst);
         float dt = src.dot(dst);
-        /* If the two vectors are parallel, cross product is zero
-         * If they point opposite, the dot product is negative */
         if (cr.norm() < eps && dt < 0) {
+            // handle corner cases with 180 degree rotations
+            // if the two vectors are parallel, cross product is zero
+            // if they point opposite, the dot product is negative
             cr = src.abs();
             if (cr(0) < cr(1)) {
                 if (cr(0) < cr(2)) {
@@ -215,7 +216,7 @@ class Quaternion : public Vector<Type, 4>
             q(0) = Type(0);
             cr = src.cross(cr);
         } else {
-            /* Half-Way Quaternion Solution */
+            // normal case, do half-way quaternion solution
             q(0) = dt + sqrt(src.norm_squared() * dst.norm_squared());
         }
         q(1) = cr(0);