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<h3 class="appendixsec">D.1 Adding New Functions</h3>

<p>The process of building the library is driven by the makefiles, which
make heavy use of special features of GNU <code>make</code>.  The makefiles
are very complex, and you probably don't want to try to understand them. 
But what they do is fairly straightforward, and only requires that you
define a few variables in the right places.

   <p>The library sources are divided into subdirectories, grouped by topic.

   <p>The <samp><span class="file">string</span></samp> subdirectory has all the string-manipulation
functions, <samp><span class="file">math</span></samp> has all the mathematical functions, etc.

   <p>Each subdirectory contains a simple makefile, called <samp><span class="file">Makefile</span></samp>,
which defines a few <code>make</code> variables and then includes the global
makefile <samp><span class="file">Rules</span></samp> with a line like:

<pre class="smallexample">     include ../Rules
</pre>
   <p class="noindent">The basic variables that a subdirectory makefile defines are:

     <dl>
<dt><code>subdir</code><dd>The name of the subdirectory, for example <samp><span class="file">stdio</span></samp>. 
This variable <strong>must</strong> be defined.

     <br><dt><code>headers</code><dd>The names of the header files in this section of the library,
such as <samp><span class="file">stdio.h</span></samp>.

     <br><dt><code>routines</code><dt><code>aux</code><dd>The names of the modules (source files) in this section of the library. 
These should be simple names, such as &lsquo;<samp><span class="samp">strlen</span></samp>&rsquo; (rather than
complete file names, such as <samp><span class="file">strlen.c</span></samp>).  Use <code>routines</code> for
modules that define functions in the library, and <code>aux</code> for
auxiliary modules containing things like data definitions.  But the
values of <code>routines</code> and <code>aux</code> are just concatenated, so there
really is no practical difference.

     <br><dt><code>tests</code><dd>The names of test programs for this section of the library.  These
should be simple names, such as &lsquo;<samp><span class="samp">tester</span></samp>&rsquo; (rather than complete file
names, such as <samp><span class="file">tester.c</span></samp>).  &lsquo;<samp><span class="samp">make&nbsp;tests</span></samp>&rsquo;<!-- /@w --> will build and
run all the test programs.  If a test program needs input, put the test
data in a file called <samp><var>test-program</var><span class="file">.input</span></samp>; it will be given to
the test program on its standard input.  If a test program wants to be
run with arguments, put the arguments (all on a single line) in a file
called <samp><var>test-program</var><span class="file">.args</span></samp>.  Test programs should exit with
zero status when the test passes, and nonzero status when the test
indicates a bug in the library or error in building.

     <br><dt><code>others</code><dd>The names of &ldquo;other&rdquo; programs associated with this section of the
library.  These are programs which are not tests per se, but are other
small programs included with the library.  They are built by
&lsquo;<samp><span class="samp">make&nbsp;others</span></samp>&rsquo;<!-- /@w -->.

     <br><dt><code>install-lib</code><dt><code>install-data</code><dt><code>install</code><dd>Files to be installed by &lsquo;<samp><span class="samp">make&nbsp;install</span></samp>&rsquo;<!-- /@w -->.  Files listed in
&lsquo;<samp><span class="samp">install-lib</span></samp>&rsquo; are installed in the directory specified by
&lsquo;<samp><span class="samp">libdir</span></samp>&rsquo; in <samp><span class="file">configparms</span></samp> or <samp><span class="file">Makeconfig</span></samp>
(see <a href="Installation.html#Installation">Installation</a>).  Files listed in <code>install-data</code> are
installed in the directory specified by &lsquo;<samp><span class="samp">datadir</span></samp>&rsquo; in
<samp><span class="file">configparms</span></samp> or <samp><span class="file">Makeconfig</span></samp>.  Files listed in <code>install</code>
are installed in the directory specified by &lsquo;<samp><span class="samp">bindir</span></samp>&rsquo; in
<samp><span class="file">configparms</span></samp> or <samp><span class="file">Makeconfig</span></samp>.

     <br><dt><code>distribute</code><dd>Other files from this subdirectory which should be put into a
distribution tar file.  You need not list here the makefile itself or
the source and header files listed in the other standard variables. 
Only define <code>distribute</code> if there are files used in an unusual way
that should go into the distribution.

     <br><dt><code>generated</code><dd>Files which are generated by <samp><span class="file">Makefile</span></samp> in this subdirectory. 
These files will be removed by &lsquo;<samp><span class="samp">make&nbsp;clean</span></samp>&rsquo;<!-- /@w -->, and they will
never go into a distribution.

     <br><dt><code>extra-objs</code><dd>Extra object files which are built by <samp><span class="file">Makefile</span></samp> in this
subdirectory.  This should be a list of file names like <samp><span class="file">foo.o</span></samp>;
the files will actually be found in whatever directory object files are
being built in.  These files will be removed by &lsquo;<samp><span class="samp">make&nbsp;clean</span></samp>&rsquo;<!-- /@w -->. 
This variable is used for secondary object files needed to build
<code>others</code> or <code>tests</code>. 
</dl>

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