From recursion to iteration.

Exercise 1.16 of 1.2.4 Exponentation in SICP.

Recursion.

(define (fast-expt b n)
  (cond ((= n 0) 1)
        ((even? n) (square (fast-expt b (/ n 2))))
        (else (* b (fast-expt b (- n 1))))))

(define (even? n)
  (= (remainder n 2) 0))

(define (square n)
  (* n n))

How do I rewrite this code to iterative process?