From 3d832af911d96731cc669fdcedbe5134841ea9ed Mon Sep 17 00:00:00 2001
From: Felix Martin <mail@felixm.de>
Date: Fri, 16 Apr 2021 19:23:29 -0400
Subject: [PATCH] Answer 5.33

---
 ex-5_31-xx.scm | 56 +++++++++++++++++++++++++++++++++++---------------
 1 file changed, 40 insertions(+), 16 deletions(-)

diff --git a/ex-5_31-xx.scm b/ex-5_31-xx.scm
index 06160e4..39d4191 100644
--- a/ex-5_31-xx.scm
+++ b/ex-5_31-xx.scm
@@ -66,6 +66,7 @@ ev-appl-did-operator-no-restore
 (display "\nex-5.33 - compare-factorial-definitions\n")
 
 (define (compile-to-file code target linkage file-name)
+  (set! label-counter 0)
   (define (write-list-to-port xs port)
     (if (null? xs)
       '()
@@ -85,22 +86,22 @@ ev-appl-did-operator-no-restore
 ; Uncomment the following lines to write the assembly code for the to methods
 ; into files.
 
-;(compile-to-file
-; '(define (factorial n)
-;    (if (= n 1)
-;        1
-;        (* (factorial (- n 1)) n)))
-; 'val 'next "factorial.sicp-asm")
-;
-;; reset label counter to the same labels for diff
+(compile-to-file
+ '(define (factorial n)
+    (if (= n 1)
+        1
+        (* (factorial (- n 1)) n)))
+ 'val 'next "factorial.sicp-asm")
+
+;(define label-counter 0)
+
+(compile-to-file
+  '(define (factorial-alt n)
+    (if (= n 1)
+        1
+        (* n (factorial-alt (- n 1)))))
+ 'val 'next "factorial-alt.sicp-asm")
 ;(define label-counter 0)
-;
-;(compile-to-file
-;  '(define (factorial-alt n)
-;    (if (= n 1)
-;        1
-;        (* n (factorial-alt (- n 1)))))
-; 'val 'next "factorial-alt.sicp-asm")
 
 ; $ diff factorial.sicp-asm factorial-alt.sicp-asm
 ; 33,36c33,34
@@ -117,8 +118,31 @@ ev-appl-did-operator-no-restore
 ; > (restore env)
 ; > (assign val (op lookup-variable-value) (const n) (reg env))
 
+; The regular factorial needs an additional save-and-restore for argl before
+; the recursive call. Argl must be saved because it contains the value of n
+; before the recursive call.
+
+; The alternative factorial needs an additional save-and-restore for env before
+; the recursive call. Env must be saved for other the evaluation of the
+; remaining arguments. In this case, the look-up of n which comes second for
+; the alternative implementation.
+
+; Neither version executes more efficiently and they have the same number of
+; instructions.
+
+(display "[answered]\n")
+
+(display "\nex-5.34 - factorial-iter\n")
+(compile-to-file
+  '(define (factorial n)
+    (define (iter product counter)
+      (if (> counter n)
+          product
+          (iter (* counter product)
+                (+ counter 1))))
+    (iter 1 1))
+ 'val 'next "factorial-iter.sicp-asm")
 
-(display "\nex-5.34\n")
 
 (display "\nex-5.35\n")