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<html>
<head>
<title>factorial</title>
<link rel="stylesheet" type="text/css" media="all" href="../man.css">
</head>
<body bgcolor=#ffffff>
<h2 align=center>factorial</h2>
<h4 align=center>OS/161 Reference Manual</h4>
<h3>Name</h3>
<p>
factorial - compute factorials using execv
</p>
<h3>Synopsis</h3>
<p>
<tt>/testbin/factorial</tt> <em>N</em>
</p>
<h3>Description</h3>
<p>
<tt>factorial</tt> computes <em>N!</em>, for integer values
<em>N</em>.
It does the computation (in bignums) by recursively calling
<A HREF=../syscall/execv.html>execv</A> on itself and is thus useful
for stressing your exec implementation.
</p>
<p>
Note that <tt>factorial</tt> does not make exec calls with
<em>large</em> argv blocks; getting to numbers large enough that the
size is interesting requires prohibitively many iterations and is
exceedingly slow.
</p>
<h3>Requirements</h3>
<p>
<tt>factorial</tt> uses the following system calls:
<ul>
<li><A HREF=../syscall/write.html>write</A></li>
<li><A HREF=../syscall/execv.html>execv</A></li>
<li><A HREF=../syscall/_exit.html>_exit</A></li>
</ul>
</p>
<p>
<tt>factorial</tt> should work once you have implemented the basic
system calls, including of course execv.
(But it depends on little other than execv, making it useful in the
early stages.)
</p>
<h3>Restrictions</h3>
<p>
Be aware that until you do the VM assignment and replace dumbvm,
running a lot of execs will run the system out of memory very
rapidly.
</p>
</body>
</html>