anchor.diff:  (defsubst slice-bounds (len start end)
     "Normalize START and END, which may be negative, to offsets
   acceptable to SUBSEQ."
  -  (declare (type signed-array-index start end)
  +  (declare (type signed-array-index start)
  +           (type signed-array-length end)
              (type array-index len))
     (values (if (minusp start)
                 (+ len start)
  
positive.code:                 (incf j))))
          ret)))
  
  (defsubst intersperse (new-elt seq)
    "Return a sequence like SEQ, but with NEW-ELT inserted between each
  element."
  
negative.code: 
  If N is negative, then |N| elements are taken (in their original
  order) from the end of SEQ."
    (check-type n signed-array-length)
    (seq-dispatch seq
      (if (minusp n)
          (last seq (abs n))
  