183 lines
7.7 KiB
HTML
183 lines
7.7 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the GNU Assembler "as".
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Copyright (C) 1991-2016 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled "GNU Free Documentation License".
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-->
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Using as: If</title>
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<meta name="description" content="Using as: If">
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<meta name="keywords" content="Using as: If">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops">
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<link href="Incbin.html#Incbin" rel="next" title="Incbin">
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<link href="Ident.html#Ident" rel="prev" title="Ident">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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-->
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</style>
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="If"></a>
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<div class="header">
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<p>
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Next: <a href="Incbin.html#Incbin" accesskey="n" rel="next">Incbin</a>, Previous: <a href="Ident.html#Ident" accesskey="p" rel="prev">Ident</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="g_t_002eif-absolute-expression"></a>
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<h3 class="section">7.41 <code>.if <var>absolute expression</var></code></h3>
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<a name="index-conditional-assembly"></a>
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<a name="index-if-directive"></a>
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<p><code>.if</code> marks the beginning of a section of code which is only
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considered part of the source program being assembled if the argument
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(which must be an <var>absolute expression</var>) is non-zero. The end of
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the conditional section of code must be marked by <code>.endif</code>
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(see <a href="Endif.html#Endif"><code>.endif</code></a>); optionally, you may include code for the
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alternative condition, flagged by <code>.else</code> (see <a href="Else.html#Else"><code>.else</code></a>).
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If you have several conditions to check, <code>.elseif</code> may be used to avoid
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nesting blocks if/else within each subsequent <code>.else</code> block.
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</p>
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<p>The following variants of <code>.if</code> are also supported:
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</p><dl compact="compact">
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<dd><a name="index-ifdef-directive"></a>
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</dd>
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<dt><code>.ifdef <var>symbol</var></code></dt>
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<dd><p>Assembles the following section of code if the specified <var>symbol</var>
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has been defined. Note a symbol which has been referenced but not yet defined
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is considered to be undefined.
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</p>
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<a name="index-ifb-directive"></a>
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</dd>
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<dt><code>.ifb <var>text</var></code></dt>
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<dd><p>Assembles the following section of code if the operand is blank (empty).
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</p>
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<a name="index-ifc-directive"></a>
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</dd>
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<dt><code>.ifc <var>string1</var>,<var>string2</var></code></dt>
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<dd><p>Assembles the following section of code if the two strings are the same. The
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strings may be optionally quoted with single quotes. If they are not quoted,
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the first string stops at the first comma, and the second string stops at the
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end of the line. Strings which contain whitespace should be quoted. The
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string comparison is case sensitive.
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</p>
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<a name="index-ifeq-directive"></a>
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</dd>
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<dt><code>.ifeq <var>absolute expression</var></code></dt>
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<dd><p>Assembles the following section of code if the argument is zero.
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</p>
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<a name="index-ifeqs-directive"></a>
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</dd>
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<dt><code>.ifeqs <var>string1</var>,<var>string2</var></code></dt>
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<dd><p>Another form of <code>.ifc</code>. The strings must be quoted using double quotes.
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</p>
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<a name="index-ifge-directive"></a>
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</dd>
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<dt><code>.ifge <var>absolute expression</var></code></dt>
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<dd><p>Assembles the following section of code if the argument is greater than or
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equal to zero.
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</p>
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<a name="index-ifgt-directive"></a>
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</dd>
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<dt><code>.ifgt <var>absolute expression</var></code></dt>
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<dd><p>Assembles the following section of code if the argument is greater than zero.
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</p>
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<a name="index-ifle-directive"></a>
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</dd>
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<dt><code>.ifle <var>absolute expression</var></code></dt>
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<dd><p>Assembles the following section of code if the argument is less than or equal
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to zero.
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</p>
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<a name="index-iflt-directive"></a>
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</dd>
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<dt><code>.iflt <var>absolute expression</var></code></dt>
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<dd><p>Assembles the following section of code if the argument is less than zero.
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</p>
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<a name="index-ifnb-directive"></a>
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</dd>
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<dt><code>.ifnb <var>text</var></code></dt>
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<dd><p>Like <code>.ifb</code>, but the sense of the test is reversed: this assembles the
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following section of code if the operand is non-blank (non-empty).
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</p>
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<a name="index-ifnc-directive"></a>
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</dd>
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<dt><code>.ifnc <var>string1</var>,<var>string2</var>.</code></dt>
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<dd><p>Like <code>.ifc</code>, but the sense of the test is reversed: this assembles the
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following section of code if the two strings are not the same.
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</p>
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<a name="index-ifndef-directive"></a>
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<a name="index-ifnotdef-directive"></a>
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</dd>
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<dt><code>.ifndef <var>symbol</var></code></dt>
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<dt><code>.ifnotdef <var>symbol</var></code></dt>
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<dd><p>Assembles the following section of code if the specified <var>symbol</var>
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has not been defined. Both spelling variants are equivalent. Note a symbol
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which has been referenced but not yet defined is considered to be undefined.
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</p>
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<a name="index-ifne-directive"></a>
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</dd>
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<dt><code>.ifne <var>absolute expression</var></code></dt>
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<dd><p>Assembles the following section of code if the argument is not equal to zero
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(in other words, this is equivalent to <code>.if</code>).
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</p>
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<a name="index-ifnes-directive"></a>
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</dd>
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<dt><code>.ifnes <var>string1</var>,<var>string2</var></code></dt>
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<dd><p>Like <code>.ifeqs</code>, but the sense of the test is reversed: this assembles the
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following section of code if the two strings are not the same.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Incbin.html#Incbin" accesskey="n" rel="next">Incbin</a>, Previous: <a href="Ident.html#Ident" accesskey="p" rel="prev">Ident</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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