anchor.diff:  	    ((null (%array-header-info array))
   	     ;; Normal array, must be backed by a simple array.
   	     (setf (%simple-array-aref (%array-header-storage array) index) value))
  -	    ((integerp (%array-header-info array))
  +	    ((fixnump (%array-header-info array))
   	     ;; Displaced array.
   	     (setf (row-major-aref (%array-header-storage array) (+ index (%array-header-info array))) value))
   	    (t ;; Direct memory access array.
  
positive.code: 	    ((null (%array-header-info array))
  	     ;; Normal array, must be backed by a simple array.
  	     (%simple-array-aref (%array-header-storage array) index))
  	    ((integerp (%array-header-info array))
  	     ;; Displaced array.
  	     (row-major-aref (%array-header-storage array) (+ index (%array-header-info array))))
  	    (t ;; Direct memory access array.
  
negative.code: 
  (defun vectorp (object)
    (or (and (%array-header-p object)
  	   (fixnump (%array-header-dimensions object)))
        (%simple-array-p object)))
  (setf (get 'vector 'type-symbol) 'vectorp)
  
  