#lang sicp

(define (square x) (* x x))
;(define (next x)
;  (if (= x 2)
;      3
;      (+ x 2)))
(define (next x) (+ x 1))

(define (smallest-divisor n)
  (find-divisor n 2))
(define (find-divisor n test-divisor)
  (cond ((> (square test-divisor) n) n)
        ((divides? test-divisor n) test-divisor)
        (else (find-divisor n (next test-divisor)))))
(define (divides? a b)
  (= (remainder b a) 0))

(define (time-sd n)
  (define start-time (runtime))
  (smallest-divisor n)
  (- (runtime) start-time))
; comparing (time-sd 100069) with the new and old versions
; it's roughly a 1.5 factor increase, likely because the if
; statement checking is slightly more expensive than simply increasing
; by one