Exercise 1.17 Multiplication by means of repeated addition
Sasha Mansurov

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    #| BEGIN (Write your solution here) |#
(define (double n)
  (* n 2))
(define (halve n)
  (/ n 2))
(define (even? n)
  (= (remainder n 2) 0))
(define (fast-mul a b)
  ; a * b + c
  (define (fast-mul-step a b c)
    (display a) (display ", ") (display b) (display ", ") (display c) (newline)
    (cond ((= b 0) c)
          ((even? b) (fast-mul-step (double a) (halve b) c))
          (else (fast-mul-step a (+ b -1) (+ c a)))))
  (fast-mul-step a b 0))

(fast-mul 8 10)
#| END |#

    #| BEGIN (Write your solution here) |#
(define (double n)
  (* n 2))
(define (halve n)
  (/ n 2))
(define (even? n)
  (= (remainder n 2) 0))
(define (fast-mul a b)
  (display a) (display ", ") (display b) (newline)
  (cond ((= b 0) 0)
        ((even? b) (double (fast-mul a (halve b))))
        (else (+ a (fast-mul a (+ b -1))))))

(fast-mul 8 10)
#| END |#

    #| BEGIN (Write your solution here) |#
(define (double n)
  (* n 2))
(define (halve n)
  (/ n 2))
(define (even? n)
  (= (remainder n 2) 0))
(define (fast-mul a b)
  ; a * b + c
  (define (fast-mul-step a b c)
    (display a) (display ", ") (display b) (display ", ") (display c) (newline)
    (cond ((= b 0) c)
          ((even? b) (fast-mul-step (double a) (halve b) c))
          (else (fast-mul-step a (+ b -1) (+ c a)))))
  (fast-mul-step a b 0))

(fast-mul 8 10)
#| END |#

    #| BEGIN (Write your solution here) |#
(define (double n)
  (* n 2))
(define (halve n)
  (/ n 2))
(define (even? n)
  (= (remainder n 2) 0))
(define (fast-mul a b)
  (display a) (display ", ") (display b) (newline)
  (cond ((= b 0) 0)
        ((even? b) (double (fast-mul a (halve b))))
        (else (+ a (fast-mul a (+ b -1))))))

(fast-mul 8 10)
#| END |#