# Pastebin o54Yop68
(defmacro with-cpring5 ((cpinternals cpindex) &body body)
  "Expose two SETF-able symbol-macros inside BODY:
     @5q   ⇔ (aref CPINTERNALS CPINDEX)
     @5phi ⇔ (aref CPINTERNALS (1+ CPINDEX))"
  (let ((vec (gensym "VEC-"))
        (idx (gensym "IDX-")))
    `(let ((,vec ,cpinternals)
           (,idx ,cpindex))
       (symbol-macrolet ((@5q   (aref ,vec ,idx))
                         (@5phi (aref ,vec (1+ ,idx))))
                  ,@body))))

(let ((v (make-array 10 :element-type 'double-float
                        :initial-contents '(0.0d0 1.0d0 2.0d0 3.0d0 4.0d0 5.0d0 6.0d0 7.0d0 8.0d0 9.0d0))))
  (with-cpring5 (v 3)
    #+(or)(setf @5q   1d0   ; v[3]  <- 1.0
          @5phi 2d0)  ; v[4]  <- 2.0
    (values @5q @5phi)))