forked from felipap/sicp-code
-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy path9A.scm
130 lines (101 loc) · 2.03 KB
/
9A.scm
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
; Lecture: 9A
; Lecturer: Harold Abelson
;# BOARD 0:03:00
(define (gcd a b)
(if (= b 0)
a
(gcd b (remainder a b))))
;# END BOARD
;# BOARD 0:15:15
(define-machine gcd
(registers a b t)
(controller
loop (branch (zero? (fetch b)) done)
(assign t (remainder (fetch a) (fetch b)))
(assign a (fetch b))
(assign b (fetch t))
(goto loop)
done))
;# END BOARD
;# SLIDE 0:22:50
(define-machine gcd
(registers a b t)
(controller
main (assign a (read))
(assign b (read))
loop (branch (zero? (fetch b)) done)
(assign t (remainder (fetch a) (fetch b)))
(assign a (fetch b))
(assign b (fetch t))
(goto loop)
done (perform (print (fetch a)))
(goto main)))
;# END SLIDE
;# BOARD 0:25:10
(define-machine (remainder n d)
(if (< n d)
n
(remainder (- n d) d)))
;# END BOARD
;;;
;;; BREAK 0:28:10
;;;
;# BOARD 0:29:10
(define (fact n)
(if (= n 1)
1
(* n (fact (- n 1)))))
;# END BOARD
;# BOARD 0:39:30
(assign continue done)
loop (branch (= 1 (fetch n)) base)
(save continue)
(save n)
(assign n (-1+ (fetch n)))
(assign continue aft)
(goto loop)
aft (restore n)
(restore continue)
(assign val (* (fetch n) (fetch val)))
(goto (fetch continue))
base (assign val (fetch n))
(goto (fetch continue))
done
;# END BOARD
;;;
;;; BREAK 0:50:50
;;;
;# BOARD 0:52:30
(define (fib n)
(if (< n 2)
n
(+ (fib (- n 1) (- n 2)))))
;# END BOARD
;# BOARD 0:54:00
(assign continue fib-done)
fib-loop ; n contains arg, continue is recipient
(branch (< (fetch n) 2) immediate-ans)
(save continue)
(assign continue after-fib-n-1)
(save n)
(assign n (- (fetch n) 1))
(goto fib-loop)
after-fib-n-1
(restore n)
; (restore continue)
(assign n (- (fetch n) 2))
; (save continue)
(assign continue after-fib-n-2)
(save val)
(goto fib-loop)
after-fib-n-2
(assign n (fetch val)); fib(n-2)
(restore val)
(restore continue)
(assign val (+ (fetch val) (fetch n)))
(goto (fetch continue))
immediate-ans
(assign val (fetch n))
(goto (fetch continue))
fib-done
;# END BOARD