anchor.diff:            (buffer-stream-start stream) (buffer-stream-start stream)))
     value)
   
  +(declaim (ftype (function (buffer-stream) (unsigned-byte 64))
  +                buffer-stream-start))
   (defun buffer-stream-start (stream)
     (buffer-stream-%start stream))
   
  
positive.code: 
  (defstruct (buffer-stream (:constructor %make-buffer-stream))
    vao
    (%start 0 :type unsigned-byte) ;; unsigned-byte ≡ (integer 0 *)
    (%start-byte (null-pointer) :type foreign-pointer)
    (length 1 :type unsigned-byte)
    (%index-type nil :type symbol)
    (%index-type-size 0 :type (unsigned-byte 8))
  
negative.code:         (type-size (buffer-stream-%index-type-size stream)))
      (when (%valid-index-type-p index-type)
        (setf (buffer-stream-%start-byte stream)
              (* value type-size))))
    value)
  
  (declaim (ftype (function (buffer-stream) (unsigned-byte 64))
                  buffer-stream-start-byte))
  (defun buffer-stream-start-byte (stream)
    (buffer-stream-%start-byte stream))
  
  (defun (setf buffer-stream-start-byte) (value stream)
    (declare (ignore value))
    (error "CEPL Internal Error: Do not set stream %start-byte directly~%~s"
           stream))
  
  