September Morn Update

Task/Fibonacci-sequence/Modula-3/fibonacci-sequence-2.mod3

@@ -0,0 +1,36 @@
+PROCEDURE IterFib(n: INTEGER): INTEGER =
+
+VAR
+
+  limit := ABS(n);
+  prev := 0;
+  curr, next: INTEGER;
+
+BEGIN
+
+  (* trivial case *)
+  IF n = 0 THEN RETURN 0; END;
+
+  IF n > 0 THEN (* positive case *)
+
+    curr := 1;
+    FOR i := 2 TO limit DO
+      next := prev + curr;
+      prev := curr;
+      curr := next;
+    END;
+
+  ELSE (* negative case *)
+
+    curr := -1;
+    FOR i := 2 TO limit DO
+      next := prev - curr;
+      prev := curr;
+      curr := next;
+    END;
+
+  END;
+
+  RETURN curr;
+
+END IterFib;