**Exercise 1.18:** Using the results of exercises 1.16 and 1.17, devise a procedure that
generates an iterative process for multiplying two integers in terms of adding, doubling,
and halving and uses a logarithmic number of steps.

```
(define (double x) (+ x x))
(define (halve x) (/ x 2))
(define (fast-mult-iter a b n)
(cond ((= b 0) n)
((even? b) (fast-mult-iter (double a) (halve b) n))
(else
(fast-mult-iter a (- b 1) (+ a n)))))
```