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<html lang="en">
<head>
<title>Word - Using as</title>
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<p>
<a name="Word"></a>Next:&nbsp;<a rel="next" accesskey="n" href="Deprecated.html#Deprecated">Deprecated</a>,
Previous:&nbsp;<a rel="previous" accesskey="p" href="Weakref.html#Weakref">Weakref</a>,
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<h3 class="section">7.120 <code>.word </code><var>expressions</var></h3>
<p><a name="index-_0040code_007bword_007d-directive-499"></a>This directive expects zero or more <var>expressions</var>, of any section,
separated by commas.
<p>The size of the number emitted, and its byte order,
depend on what target computer the assembly is for.
<!-- on amd29k, i960, sparc the "special treatment to support compilers" doesn't -->
<!-- happen-32-bit addressability, period; no long/short jumps. -->
<p><a name="index-difference-tables-altered-500"></a><a name="index-altered-difference-tables-501"></a><blockquote>
<em>Warning: Special Treatment to support Compilers</em>
</blockquote>
<p>Machines with a 32-bit address space, but that do less than 32-bit
addressing, require the following special treatment. If the machine of
interest to you does 32-bit addressing (or doesn't require it;
see <a href="Machine-Dependencies.html#Machine-Dependencies">Machine Dependencies</a>), you can ignore this issue.
<p>In order to assemble compiler output into something that works,
<span class="command">as</span> occasionally does strange things to <span class="samp">.word</span> directives.
Directives of the form <span class="samp">.word sym1-sym2</span> are often emitted by
compilers as part of jump tables. Therefore, when <span class="command">as</span> assembles a
directive of the form <span class="samp">.word sym1-sym2</span>, and the difference between
<code>sym1</code> and <code>sym2</code> does not fit in 16 bits, <span class="command">as</span>
creates a <dfn>secondary jump table</dfn>, immediately before the next label.
This secondary jump table is preceded by a short-jump to the
first byte after the secondary table. This short-jump prevents the flow
of control from accidentally falling into the new table. Inside the
table is a long-jump to <code>sym2</code>. The original <span class="samp">.word</span>
contains <code>sym1</code> minus the address of the long-jump to
<code>sym2</code>.
<p>If there were several occurrences of <span class="samp">.word sym1-sym2</span> before the
secondary jump table, all of them are adjusted. If there was a
<span class="samp">.word sym3-sym4</span>, that also did not fit in sixteen bits, a
long-jump to <code>sym4</code> is included in the secondary jump table,
and the <code>.word</code> directives are adjusted to contain <code>sym3</code>
minus the address of the long-jump to <code>sym4</code>; and so on, for as many
entries in the original jump table as necessary.
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