-;;; Given a byte vector Vec and an index variable Index, read a variable
-;;; length integer and advance index.
+;;; Given a byte vector VEC and an index variable INDEX, read a
+;;; variable length integer and advance index.
+;;;
+;;; FIXME: This is called O(20) times. It should be reimplemented
+;;; with much of its logic in a single service function which can
+;;; be called by the macro expansion:
+;;; `(SETF ,INDEX (%READ-VAR-INTEGER ,VEC ,INDEX)).