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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>3. Preprocessing</title>
<link rel="stylesheet" type="text/css" href="Frontpage.css">
<link rel="stylesheet" type="text/css" href="languages.css">
<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
<link rel="home" href="sleigh.html" title="SLEIGH">
<link rel="up" href="sleigh.html" title="SLEIGH">
<link rel="prev" href="sleigh_layout.html" title="2. Basic Specification Layout">
<link rel="next" href="sleigh_definitions.html" title="4. Basic Definitions">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<div class="navheader">
<table width="100%" summary="Navigation header">
<tr><th colspan="3" align="center">3. Preprocessing</th></tr>
<tr>
<td width="20%" align="left">
<a accesskey="p" href="sleigh_layout.html">Prev</a> </td>
<th width="60%" align="center"> </th>
<td width="20%" align="right"> <a accesskey="n" href="sleigh_definitions.html">Next</a>
</td>
</tr>
</table>
<hr>
</div>
<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="sleigh_preprocessing"></a>3. Preprocessing</h2></div></div></div>
<p>
SLEIGH provides support for simple file inclusion, macros, and other
basic preprocessing functions. These are all invoked with directives
that start with the &#8216;@&#8217; character, which must be the first character
in the line.
</p>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="sleigh_including_files"></a>3.1. Including Files</h3></div></div></div>
<p>
In general a single SLEIGH specification is contained in a single
file, and the compiler is invoked on one file at a time. Multiple
files can be put together for one specification by using
the <span class="bold"><strong>@include</strong></span> directive. This must
appear at the beginning of the line and is followed by the path name
of the file to be included, enclosed in double quotes.
</p>
<div class="informalexample"><code class="code">@include "example.slaspec"</code></div>
<p>
Parsing proceeds as if the entire line is replaced with the contents
of the indicated file. Multiple inclusions are possible, and the
included files can have their
own <span class="bold"><strong>@include</strong></span> directives.
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="idm140526920968368"></a>3.2. Preprocessor Macros</h3></div></div></div>
<p>
SLEIGH allows simple (unparameterized) macro definitions and
expansions. A macro definition occurs on one line and starts with
the <span class="bold"><strong>@define</strong></span> directive. This is
followed by an identifier for the macro and then a string to which the
macro should expand. The string must either be a proper identifier
itself or surrounded with double quotes. The macro can then be
expanded with typical &#8220;$(identifier)&#8221; syntax at any other point in the
specification following the definition.
</p>
<div class="informalexample"><pre class="programlisting">
@define ENDIAN "big"
<span class="weak">...</span>
define endian=$(ENDIAN);
</pre></div>
<p>
This example defines a macro identified as <span class="emphasis"><em>ENDIAN</em></span>
with the string &#8220;big&#8221;, and then expands the macro in a later SLEIGH
statement. Macro definitions can also be made from the command line
and in the &#8220;.spec&#8221; file, allowing multiple specification variations to
be derived from one file. SLEIGH also has
an <span class="bold"><strong>@undef</strong></span> directive which removes the
definition of a macro from that point on in the file.
</p>
<div class="informalexample"><code class="code">@undef ENDIAN</code></div>
<p>
</p>
</div>
<div class="sect2">
<div class="titlepage"><div><div><h3 class="title">
<a name="idm140526920961536"></a>3.3. Conditional Compilation</h3></div></div></div>
<p>
SLEIGH supports several directives that allow conditional inclusion of
parts of a specification, based on the existence of a macro, or its
value. The lines of the specification to be conditionally included are
bounded by one of the <span class="bold"><strong>@if...</strong></span>
directives described below and at the bottom by
the <span class="bold"><strong>@endif</strong></span> directive. If the
condition described by the <span class="bold"><strong>@if...</strong></span>
directive is true, the bounded lines are evaluated as part of the
specification, otherwise they are skipped. Nesting of these directives
is allowed: a
second <span class="bold"><strong>@if...</strong></span> <span class="bold"><strong>@endif</strong></span>
pair can occur inside an initial <span class="bold"><strong>@if</strong></span>
and <span class="bold"><strong>@endif</strong></span>.
</p>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="idm140526920955392"></a>3.3.1. @ifdef and @ifndef</h4></div></div></div>
<p>
The <span class="bold"><strong>@ifdef</strong></span> directive is followed by a
macro identifier and evaluates to true if the macro is defined.
The <span class="bold"><strong>@ifndef</strong></span> directive is similar
except it evaluates to true if the macro identifier
is <span class="emphasis"><em>not</em></span> defined.
</p>
<div class="informalexample"><pre class="programlisting">
@ifdef ENDIAN
define endian=$(ENDIAN);
@else
define endian=little;
@endif
</pre></div>
<p>
This directive can only take a single identifier as an argument, any
other form is flagged as an error. For logically combining a test of
whether a macro is defined with other tests, use
the <span class="bold"><strong>defined</strong></span> operator in
an <span class="bold"><strong>@if</strong></span>
or <span class="bold"><strong>@elif</strong></span> directive (See below).
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="idm140526920949120"></a>3.3.2. @if</h4></div></div></div>
<p>
The <span class="bold"><strong>@if</strong></span> directive is followed by a
boolean expression with macros as the variables and strings as the
constants. Comparisons between macros and strings are currently
limited to string equality or inequality. But individual comparisons
can be combined arbitrarily using parentheses and the boolean
operators &#8216;&amp;&amp;&#8217;, &#8216;||&#8217;, and &#8216;^^&#8217;. These represent a <span class="emphasis"><em>logical
and</em></span>, a <span class="emphasis"><em>logical or</em></span>, and
a <span class="emphasis"><em>logical exclusive-or</em></span> operation respectively. It
is possible to test whether a particular macro is defined within the
boolean expression for an <span class="bold"><strong>@if</strong></span>
directive, by using the <span class="bold"><strong>defined</strong></span>
operator. This exists as a keyword and a functional operator only
within a preprocessor boolean
expression. The <span class="bold"><strong>defined</strong></span> keyword takes
as argument a macro identifier, and it evaluates to true if the macro
is defined.
</p>
<div class="informalexample"><pre class="programlisting">
@if defined(X_EXTENSION) || (VERSION == "5")
...
@endif
</pre></div>
<p>
</p>
</div>
<div class="sect3">
<div class="titlepage"><div><div><h4 class="title">
<a name="idm140526920942032"></a>3.3.3. @else and @elif</h4></div></div></div>
<p>
An <span class="bold"><strong>@else</strong></span> directive splits the lines
bounded by an <span class="bold"><strong>@if</strong></span> directive and
an <span class="bold"><strong>@endif</strong></span> directive into two
parts. The first part is included in the processing if the
initial <span class="bold"><strong>@if</strong></span> directive evaluates to
true, otherwise the second part is included.
</p>
<p>
The <span class="bold"><strong>@elif</strong></span> directive splits the
bounded lines up as with <span class="bold"><strong>@else</strong></span>, but
the second part is included only if the
previous <span class="bold"><strong>@if</strong></span> was false and the
condition specified in the <span class="bold"><strong>@elif</strong></span>
itself is true. Between one <span class="bold"><strong>@if</strong></span>
and <span class="bold"><strong>@endif</strong></span> pair, there can be
multiple <span class="bold"><strong>@elif</strong></span> directives, but only
one <span class="bold"><strong>@else</strong></span>, which must occur after all
the <span class="bold"><strong>@elif</strong></span> directives.
</p>
<div class="informalexample"><pre class="programlisting">
@if PROCESSOR == &#8220;mips&#8221;
@ define ENDIAN &#8220;big&#8221;
@elif ((PROCESSOR==&#8221;x86&#8221;)&amp;&amp;(OS!=&#8221;win&#8221;))
@ define ENDIAN &#8220;little&#8221;
@else
@ define ENDIAN &#8220;unknown&#8221;
@endif
</pre></div>
<p>
</p>
</div>
</div>
</div>
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<hr>
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<tr>
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<td width="20%" align="center"> </td>
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</td>
</tr>
<tr>
<td width="40%" align="left" valign="top">2. Basic Specification Layout </td>
<td width="20%" align="center"><a accesskey="h" href="sleigh.html">Home</a></td>
<td width="40%" align="right" valign="top"> 4. Basic Definitions</td>
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