From 82128a64451fb314f31786580d4268619f973eb0 Mon Sep 17 00:00:00 2001
From: Felix Martin <mail@felixm.de>
Date: Sun, 21 Mar 2021 09:35:06 -0400
Subject: [PATCH] Implement till 5.6

---
 ex-5_01-xx.scm => ex-5_01-06.scm | 74 ++++++++++++++++++++++++++++++++
 ex-5_07-xx.scm                   |  8 ++++
 2 files changed, 82 insertions(+)
 rename ex-5_01-xx.scm => ex-5_01-06.scm (67%)
 create mode 100644 ex-5_07-xx.scm

diff --git a/ex-5_01-xx.scm b/ex-5_01-06.scm
similarity index 67%
rename from ex-5_01-xx.scm
rename to ex-5_01-06.scm
index ea010a8..1bfc43c 100644
--- a/ex-5_01-xx.scm
+++ b/ex-5_01-06.scm
@@ -161,4 +161,78 @@
         (expt-iter 3 4))
 
 (display "\nex-5.5 - hand-simulate-fib\n")
+(display "[answered]\n")
+
+; begin
+; n = 2 ; val = ? ; continue = fib-done
+; stack = []
+
+; fib-loop
+; n = 1 ; val = ? ; continue = afterfib-n-1
+; stack = [2, fib-done]
+
+; fib-loop
+; immediate-answer
+; n = 1 ; val = 1 ; continue = afterfib-n-1
+; stack = [2, fib-done]
+
+; afterfib-n-1
+; n = 0 ; val = 1 ; continue = afterfib-n-2
+; stack = [1, fib-done]
+
+; fib-loop
+; n = 0 ; val = 0 ; continue = afterfib-n-2
+; stack = [1, fib-done]
+
+; afterfib-n-2
+; n = 0 ; val = 1 ; continue = fib-done
+; stack = []
+
+; fib-done
+; val = 1
+
+(display "\nex-5.6 - slightly-improved-fib\n")
+
+(define fib-machine
+  (make-machine
+    '(n val continue)
+    (list (list '< <) (list '- -) (list '= +) (list '+ +))
+    '(controller
+        (assign continue (label fib-done))
+      fib-loop
+        (test (op <) (reg n) (const 2))
+        (branch (label immediate-answer))
+        ;; set up to compute Fib(n - 1)
+        (save continue)
+        (assign continue (label afterfib-n-1))
+        (save n)                           ; save old value of n
+        (assign n (op -) (reg n) (const 1)); clobber n to n - 1
+        (goto (label fib-loop))            ; perform recursive call
+      afterfib-n-1                         ; upon return, val contains Fib(n - 1)
+        (restore n)
+        ;(restore continue)
+        ;; set up to compute Fib(n - 2)
+        (assign n (op -) (reg n) (const 2))
+        ;(save continue)
+        (assign continue (label afterfib-n-2))
+        (save val)                         ; save Fib(n - 1)
+        (goto (label fib-loop))
+      afterfib-n-2                         ; upon return, val contains Fib(n - 2)
+        (assign n (reg val))               ; n now contains Fib(n - 2)
+        (restore val)                      ; val now contains Fib(n - 1)
+        (assign val                        ;  Fib(n - 1) +  Fib(n - 2)
+                (op +) (reg val) (reg n))
+        (restore continue)
+        (goto (reg continue))              ; return to caller, answer is in val
+      immediate-answer
+        (assign val (reg n))               ; base case:  Fib(n) = n
+        (goto (reg continue))
+      fib-done)))
+
+(set-register-contents! fib-machine 'n 8)
+(start fib-machine)
+(assert (get-register-contents fib-machine 'val) 21)
+
+; restore and save of continue in afterfib-n-1 is not needed
+(display "[answered]\n")
 
diff --git a/ex-5_07-xx.scm b/ex-5_07-xx.scm
new file mode 100644
index 0000000..af52201
--- /dev/null
+++ b/ex-5_07-xx.scm
@@ -0,0 +1,8 @@
+(load "util.scm")
+(load "misc/sicp-regsim.scm")
+
+
+(display "\nex-5.7\n")
+
+
+(display "\nex-5.8\n")