anchor.diff:      (decf (atomic-integer-cell atomic-integer) delta)))
   
   (defun atomic-integer-incf (atomic-integer &optional (delta 1))
  +  "Increments the value of `ATOMIC-INTEGER` by `DELTA`.
  +
  +Returns the new value of `ATOMIC-INTEGER`."
     (declare (type atomic-integer atomic-integer)
              (type %atomic-integer-value delta)
              (optimize (safety 0) (speed 3)))
  
positive.code:   (signal-not-implemented 'make-atomic-integer))
  
  (defun atomic-integer-cas (atomic-integer old new)
    (declare (type atomic-integer atomic-integer)
             (type %atomic-integer-value old new)
             (optimize (safety 0) (speed 3)))
  
negative.code:       (t nil))))
  
  (defun atomic-integer-decf (atomic-integer &optional (delta 1))
    "Decrements the value of `ATOMIC-INTEGER` by `DELTA`.
  
  Returns the new value of `ATOMIC-INTEGER`."
    (declare (type atomic-integer atomic-integer)
             (type %atomic-integer-value delta)
             (optimize (safety 0) (speed 3)))
  