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+#lang sicp
+(#%require (only racket/base print-as-expression print-mpair-curly-braces))
+(print-as-expression #f)
+(print-mpair-curly-braces #f)
+
+;; Chapter 5
+;; Computing with Register Machines
+
+;; 5.1
+;; Designing Register Machines
+
+(define (gcd a b)
+  (if (= b 0)
+    a
+    (gcd b (remainder a b))))
+
+#| 5.1 |#
+
+(define (factorial n)
+  (define (iter product counter)
+    (if (> counter n)
+      product
+      (iter
+        (* counter product)
+        (+ counter 1))))
+  (iter 1 1))
+
+;; A Language for Describing Register Machines
+
+(define gcd-data-paths
+  '(data-paths
+     (registers
+       ((name a)
+        (buttons ((name a<-b) (source (register b)))))
+       ((name b)
+        (buttons ((name b<-t) (source (register t)))))
+       ((name t)
+        (buttons ((name t<-r) (source (operation rem))))))
+     (operations
+       ((name rem)
+        (inpus (register a) (register b)))
+       ((name =)
+        (inputs (register b) (constant 0))))))
+
+(define gcd-controller
+  '(controller
+    test-b
+      (test =)
+      (branch (label gcd-done))
+      (t<-r)
+      (a<-b)
+      (b<-t)
+      (goto (label test-b))
+    gcd-done))
+
+(define gcd-succinct
+  '(controller
+    test-b
+      (test (op =) (reg b) (const 0))
+      (branch (label gcd-done))
+      (assign t (op rem) (reg a) (reg b))
+      (assign a (reg b))
+      (assign b (reg t))
+      (goto (label test-b))
+    gcd-done))
+
+#| 5.2 |#
+
+(define factorial-controller
+  '(controller
+      (assign product (const 1))
+      (assign counter (const 1))
+    test-counter
+      (test (op >) (reg counter) (reg n))
+      (branch (label fact-done))
+      (assign product (op *) (reg counter) (reg product))
+      (assign counter (op +) (reg counter) (const 1))
+      (goto (label test-counter))
+    fact-done))
+
+(define gcd-new
+  '(controller
+    gcd-loop
+      (assign a (op read))
+      (assign b (op read))
+    test-b
+      (test (op =) (reg b) (const 0))
+      (branch (label gcd-done))
+      (assign t (op rem) (reg a) (reg b))
+      (assign a (reg b))
+      (assign b (reg t))
+      (goto (label test-b))
+    gcd-done
+      (perform (op print) (reg a))
+      (goto (label gcd-loop))))
+
+;; Abstraction in Machine Design
+
+(define (remainder n d)
+  (if (< n d)
+    n
+    (remainder (- n d) d)))
+
+(define gcd-prim
+  '(controller
+    test-b
+      (test (op =) (reg b) (const 0))
+      (branch (label gcd-done))
+      (assign t (reg a))
+    rem-loop
+      (test (op <) (reg t) (reg b))
+      (branch (label rem-done))
+      (assign t (op -) (reg t) (reg b))
+      (goto (label rem-loop))
+    rem-done
+      (assign a (reg b))
+      (assign b (reg t))
+      (goto (label test-b))
+    gcd-done))
+
+#| 5.3 |#
+
+(define (sqrt x)
+  (define (square x) (* x x))
+  (define (average a b) (/ (+ a b) 2))
+  (define (good-enough? guess)
+    (< (abs (- (square guess) x)) 0.001))
+  (define (improve guess)
+    (average guess (/ x guess)))
+  (define (sqrt-iter guess)
+    (if (good-enough? guess)
+      guess
+      (sqrt-iter (improve guess))))
+  (sqrt-iter 1.0))
+
+(define sqrt-controller-1
+  '(controller
+      (assign guess (const 1.0))
+    test-guess
+      (test (op good-enough?) (reg guess))
+      (branch (label sqrt-done))
+      (assign guess (op improve) (reg guess))
+      (goto (label test-guess))
+    sqrt-done))
+
+(define sqrt-controller-2
+  '(controller
+      (assign guess (const 1.0))
+    test-guess
+      (test (op good-enough?) (reg guess))
+      (branch (label sqrt-done))
+      (assign t (op /) (reg x) (reg guess))
+      (assign guess (op average) (reg guess) (reg t))
+      (goto (label test-guess))
+    sqrt-done))
+
+(define sqrt-controller-3
+  '(controller
+      (assign guess (const 1.0))
+    test-guess
+      (test (op good-enough?) (reg guess))
+      (branch (label sqrt-done))
+      (assign t (op /) (reg x) (reg guess))
+      (assign t (op +) (reg t) (reg guess))
+      (assign guess (op /) (reg t) (const 2))
+      (goto (label test-guess))
+    sqrt-done))
+
+(define sqrt-controller-4
+  '(controller
+      (assign guess (const 1.0))
+    test-guess
+      (assign t (op *) (reg guess) (reg guess))
+      (assign t (op -) (reg t) x)
+      (assign t (op abs) (reg t))
+      (test (op <) (reg t) (const 0.001))
+      (branch (label sqrt-done))
+      (assign t (op /) (reg x) (reg guess))
+      (assign t (op +) (reg t) (reg guess))
+      (assign guess (op /) (reg t) (const 2))
+      (goto (label test-guess))
+    sqrt-done))
+
+;; Subroutines
+
+(define gcd-twice
+  '(controller
+    gcd-1
+      (test (op =) (reg b) (const 0))
+      (branch (label after-gcd-1))
+      (assign t (op rem) (reg a) (reg b))
+      (assign a (reg b))
+      (assign b (reg t))
+      (goto (label gcd-1))
+    after-gcd-1
+      ; ...
+    gcd-2
+      (test (op =) (reg b) (const 0))
+      (branch (label after-gcd-2))
+      (assign t (op rem) (reg a) (reg b))
+      (assign a (reg b))
+      (assign b (reg t))
+      (goto (label gcd-2))
+    after-gcd-2))
+
+(define gcd-sub
+  '(controller
+    gcd
+      (test (op =) (reg b) (const 0))
+      (branch (label gcd-done))
+      (assign t (op rem) (reg a) (reg b))
+      (assign a (reg b))
+      (assign b (reg t))
+      (goto (label gcd))
+    gcd-done
+      (test (op =) (reg continue) (const 0))
+      (branch (label after-gcd-1))
+      (goto (label after-gcd-2))
+      ; ...
+      (assign continue (const 0))
+      (goto (label gcd))
+    after-gcd-1
+      ; ...
+      (assign continue (const 1))
+      (goto (label gcd)
+    after-gcd-2)))
+
+(define gcd-sub-label
+  '(controller
+    gcd
+      (test (op =) (reg b) (const 0))
+      (branch (label gcd-done))
+      (assign t (op rem) (reg a) (reg b))
+      (assign a (reg b))
+      (assign b (reg t))
+      (goto (label gcd))
+    gcd-done
+      (goto (reg continue))
+      ; ...
+      (assign continue (label after-gcd-1))
+      (goto (label gcd))
+    after-gcd-1
+      ; ...
+      (assign continue (label after-gcd-2))
+      (goto (label gcd)
+    after-gcd-2)))
+
+;; Using a Stack to Implement Recursion
+
+(define (factorial-rec n)
+  (if (= n 1)
+    1
+    (* (factorial (- n 1)) n)))
+
+(define fact-controller
+  '(controller
+      (assign (continue (label fact-done)))
+    fact-loop
+      (test (op =) (reg n) (const 1))
+      (branch (label base-case))
+      (save continue)
+      (save n)
+      (assign n (op -) (reg n) (const 1))
+      (assign continue (label after-fact))
+      (goto (label fact-loop))
+    after-fact
+      (restore n)
+      (restore continue)
+      (assign val (op *) (reg n) (reg val))
+      (goto (reg continue))
+    base-case
+      (assign val (const 1))
+      (goto (reg continue))
+    fact-done))
+
+(define (fib n)
+  (if (< n 2)
+    n
+    (+ (fib (- n 1)) (fib (- n 2)))))
+
+(define fib-controller
+  '(controller
+      (assign continue (label fib-done))
+    fib-loop
+      (test (op <) (reg n) (const 2))
+      (branch (label immediate answer))
+      (save continue)
+      (assign continue (label afterfib-n-1))
+      (save n)
+      (assign n (op -) (reg n) (const 1))
+      (goto (label fib-loop))
+    afterfib-n-1
+      (restore n)
+      (restore continue)
+      (assign n (op -) (reg n) (const 2))
+      (save continue)
+      (assign continue (label afterfib-n-2))
+      (save val)
+      (goto (label fib-loop))
+    afterfib-n-2
+      (assign n (reg val))
+      (restore val)
+      (restore continue)
+      (assign val (op +) (reg val) (reg n))
+      (goto (reg continue))
+    immediate-answer
+      (assign val (reg n))
+      (goto (reg continue))
+    fib-done))
+
+#| 5.4 |#
+
+(define (expt b n)
+  (if (= n 0)
+    1
+    (* b (expt b (- n 1)))))
+
+(define expt-controller
+  '(controller
+      (assign (continue (label expt-done)))
+    expt-loop
+      (test (op =) (reg n) (const 0))
+      (branch (label base-case))
+      (save continue)
+      (save n)
+      (assign n (op -) (reg n) (const 1))
+      (assign continue (label after-expt))
+      (goto (label expt-loop))
+    after-expt
+      (restore n)
+      (restore continue)
+      (assign val (op *) (reg b) (reg val))
+      (goto (reg continue))
+    base-case
+      (assign val (const 1))
+      (goto (reg continue))
+    expt-done))
+
+(define (expt- b n)
+  (define (expt-iter counter product)
+    (if (= counter 0)
+      product
+      (expt-iter (- counter 1) (* b product))))
+  (expt-iter n 1))
+
+(define expt-iter-controller
+  '(controller
+      (assign counter (reg n))
+      (assign product (const 1))
+    test-counter
+      (test (op =) (reg counter) (const 0))
+      (branch (label expt-done))
+      (assign counter (op -) (reg counter) (const 1))
+      (assign product (op *) (reg b) (reg product))
+      (goto (label test-counter))
+    expt-done))
+
+#| 5.6 |#
+
+(define fib-controller-trimmed
+  '(controller
+      (assign continue (label fib-done))
+    fib-loop
+      (test (op <) (reg n) (const 2))
+      (branch (label immediate answer))
+      (save continue)
+      (assign continue (label afterfib-n-1))
+      (save n)
+      (assign n (op -) (reg n) (const 1))
+      (goto (label fib-loop))
+    afterfib-n-1
+      (restore n)
+      ;; (restore continue)
+      (assign n (op -) (reg n) (const 2))
+      ;; (save continue)
+      (assign continue (label afterfib-n-2))
+      (save val)
+      (goto (label fib-loop))
+    afterfib-n-2
+      (assign n (reg val))
+      (restore val)
+      (restore continue)
+      (assign val (op +) (reg val) (reg n))
+      (goto (reg continue))
+    immediate-answer
+      (assign val (reg n))
+      (goto (reg continue))
+    fib-done))
+
+;; Instruction Summary
+
+#| (assign [register-name] (reg [register-name])) |#
+#| (assign [register-name] (const [constant-value])) |#
+#| (assign [register-name] (op [operation-name]) [input-1] ... [input-n]) |#
+#| (perform (op [operation-name]) [input-1] ... [input-n]) |#
+#| (test (op [operation-name]) [input-1] ... [input-n]) |#
+#| (branch (label [label-name])) |#
+#| (goto (label [label-name])) |#
+
+#| (assign [register-name] (label [label-name])) |#
+#| (goto (reg [register-name])) |#
+
+#| (save [register-name]) |#
+#| (restore [register-name]) |#