fixes #859

xml/chapter5/section1/section1.xml

@@ -202,6 +202,48 @@ function factorial(n) {
 }    
       </JAVASCRIPT>
     </SNIPPET>
+    <SOLUTION>
+      (Solution by GitHub user escolmebartlebooth)
+      In <JAVASCRIPTINLINE>factorial(n)</JAVASCRIPTINLINE>, the function
+      <JAVASCRIPTINLINE>iter(product, counter)</JAVASCRIPTINLINE> is seeded by the
+      arguments <JAVASCRIPTINLINE>(1, 1)</JAVASCRIPTINLINE> and runs until
+      <JAVASCRIPTINLINE>counter > n</JAVASCRIPTINLINE>, at which point the product is
+      returned. Unlike <JVASCRIPTINLINE>gcd(a, b)</JVASCRIPTINLINE>, the register
+      machine has no need of a temporary register assuming that the correct order of
+      register assignment is followed.
+
+      For the data path, we see three registers:
+      <JAVASCRIPTINLINE>product</JAVASCRIPTINLINE>,
+      <JAVASCRIPTINLINE>counter</JAVASCRIPTINLINE>, and
+      <JAVASCRIPTINLINE>n</JAVASCRIPTINLINE>. There are two operations:
+      <JAVASCRIPTINLINE>multiply</JAVASCRIPTINLINE> and
+      <JAVASCRIPTINLINE>plus</JAVASCRIPTINLINE> with two assignments.
+      There is one test: <JAVASCRIPTINLINE>greater than</JAVASCRIPTINLINE>.
+
+      <FIGURE src="img_javascript/ex5-1-solution-1.png">
+	<LABEL NAME= "ex:5-1"/>
+      </FIGURE>
+
+      For the controller, we start by filling the three registers with the desired
+      factorial <JAVASCRIPTINLINE>n</JAVASCRIPTINLINE> and the value
+      <JAVASCRIPTINLINE>1</JAVASCRIPTINLINE> (seeding
+      <JAVASCRIPTINLINE>product</JAVASCRIPTINLINE> and
+      <JAVASCRIPTINLINE>counter</JAVASCRIPTINLINE>). The function
+      <JAVASCRIPTINLINE>iter</JAVASCRIPTINLINE> runs and tests whether
+      <JAVASCRIPTINLINE>counter > n</JAVASCRIPTINLINE>. If
+      <JAVASCRIPTINLINE>counter &lt;= n</JAVASCRIPTINLINE>, then
+      <JAVASCRIPTINLINE>product</JAVASCRIPTINLINE> is updated to
+      <JAVASCRIPTINLINE>product * counter</JAVASCRIPTINLINE>, followed by counter being
+      updated to
+      <JAVASCRIPTINLINE>counter + 1</JAVASCRIPTINLINE> and the process is repeated until
+      <JAVASCRIPTINLINE>counter > n</JAVASCRIPTINLINE>. Once counter is > n, the product
+      is
+      <JAVASCRIPTINLINE>factorial(n)</JAVASCRIPTINLINE> and can be returned.
+
+      <FIGURE src="img_javascript/ex5-1-solution-2.png">
+	<LABEL NAME= "ex:5-1-2"/>
+      </FIGURE>
+    </SOLUTION>
   </EXERCISE>
 
   <INDEX>data paths for register machine<CLOSE/></INDEX>