Fix wrong LOOP form: it contained FOR and UNTIL statements mixed in a…

…n invalid and undefined way, as per the ANSI standard: http://www.lispworks.com/documentation/HyperSpec/Body/06_aba.htm "The iteration control clauses for, as, and repeat must precede any other loop clauses, except initially, with, and named, since they establish variable bindings."

src/math.lisp

@@ -8,16 +8,16 @@ denominator."
            (type integer a b))
   (assert (and (>= a 0)
                (>= b 0)))
-  (loop
-     for c = a then (- d (* q c))
-     and d = b then c
-     for u_c = 1 then (- u_d (* q u_c))
-     and v_c = 0 then (- v_d (* q v_c))
-     and u_d = 0 then u_c
-     and v_d = 1 then v_c
-     until (= c 0)
-     for q = (floor d c)
-     finally (return (values d u_d v_d))))
+  (do ((q 0)
+       (c a (- d (* q c)))
+       (d b c)
+       (u_c 1 (- u_d (* q u_c)))
+       (v_c 0 (- v_d (* q v_c)))
+       (u_d 0 u_c)
+       (v_d 1 v_c))
+      ((= c 0)
+       (values d u_d v_d))
+   (setq q (floor d c))))
 
 (defconst +small-primes+
   (make-array 269