90 lines
2.9 KiB
HTML
90 lines
2.9 KiB
HTML
<!--
|
|
Copyright (c) 2015
|
|
The President and Fellows of Harvard College.
|
|
|
|
Redistribution and use in source and binary forms, with or without
|
|
modification, are permitted provided that the following conditions
|
|
are met:
|
|
1. Redistributions of source code must retain the above copyright
|
|
notice, this list of conditions and the following disclaimer.
|
|
2. Redistributions in binary form must reproduce the above copyright
|
|
notice, this list of conditions and the following disclaimer in the
|
|
documentation and/or other materials provided with the distribution.
|
|
3. Neither the name of the University nor the names of its contributors
|
|
may be used to endorse or promote products derived from this software
|
|
without specific prior written permission.
|
|
|
|
THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
|
|
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
ARE DISCLAIMED. IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
|
|
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
SUCH DAMAGE.
|
|
-->
|
|
<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>
|