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107 lines
6.5 KiB
HTML
107 lines
6.5 KiB
HTML
4 years ago
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<html lang="en">
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<title>If - Using as</title>
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<meta name="description" content="Using as">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Pseudo-Ops.html#Pseudo-Ops" title="Pseudo Ops">
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<link rel="prev" href="Ident.html#Ident" title="Ident">
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<link rel="next" href="Incbin.html#Incbin" title="Incbin">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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This file documents the GNU Assembler "as".
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Copyright (C) 1991-2015 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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</head>
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<body>
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<div class="node">
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<a name="If"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Incbin.html#Incbin">Incbin</a>,
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Previous: <a rel="previous" accesskey="p" href="Ident.html#Ident">Ident</a>,
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Up: <a rel="up" accesskey="u" href="Pseudo-Ops.html#Pseudo-Ops">Pseudo Ops</a>
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<hr>
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</div>
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<h3 class="section">7.41 <code>.if </code><var>absolute expression</var></h3>
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<p><a name="index-conditional-assembly-356"></a><a name="index-g_t_0040code_007bif_007d-directive-357"></a><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>The following variants of <code>.if</code> are also supported:
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<a name="index-g_t_0040code_007bifdef_007d-directive-358"></a>
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<dl><dt><code>.ifdef </code><var>symbol</var><dd>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><a name="index-g_t_0040code_007bifb_007d-directive-359"></a><br><dt><code>.ifb </code><var>text</var><dd>Assembles the following section of code if the operand is blank (empty).
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<p><a name="index-g_t_0040code_007bifc_007d-directive-360"></a><br><dt><code>.ifc </code><var>string1</var><code>,</code><var>string2</var><dd>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><a name="index-g_t_0040code_007bifeq_007d-directive-361"></a><br><dt><code>.ifeq </code><var>absolute expression</var><dd>Assembles the following section of code if the argument is zero.
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<p><a name="index-g_t_0040code_007bifeqs_007d-directive-362"></a><br><dt><code>.ifeqs </code><var>string1</var><code>,</code><var>string2</var><dd>Another form of <code>.ifc</code>. The strings must be quoted using double quotes.
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<p><a name="index-g_t_0040code_007bifge_007d-directive-363"></a><br><dt><code>.ifge </code><var>absolute expression</var><dd>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><a name="index-g_t_0040code_007bifgt_007d-directive-364"></a><br><dt><code>.ifgt </code><var>absolute expression</var><dd>Assembles the following section of code if the argument is greater than zero.
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<p><a name="index-g_t_0040code_007bifle_007d-directive-365"></a><br><dt><code>.ifle </code><var>absolute expression</var><dd>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><a name="index-g_t_0040code_007biflt_007d-directive-366"></a><br><dt><code>.iflt </code><var>absolute expression</var><dd>Assembles the following section of code if the argument is less than zero.
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<p><a name="index-g_t_0040code_007bifnb_007d-directive-367"></a><br><dt><code>.ifnb </code><var>text</var><dd>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><a name="index-g_t_0040code_007bifnc_007d-directive-368"></a><br><dt><code>.ifnc </code><var>string1</var><code>,</code><var>string2</var><code>.</code><dd>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><a name="index-g_t_0040code_007bifndef_007d-directive-369"></a><a name="index-g_t_0040code_007bifnotdef_007d-directive-370"></a><br><dt><code>.ifndef </code><var>symbol</var><dt><code>.ifnotdef </code><var>symbol</var><dd>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><a name="index-g_t_0040code_007bifne_007d-directive-371"></a><br><dt><code>.ifne </code><var>absolute expression</var><dd>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><a name="index-g_t_0040code_007bifnes_007d-directive-372"></a><br><dt><code>.ifnes </code><var>string1</var><code>,</code><var>string2</var><dd>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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</dl>
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</body></html>
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