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<a name="AT_0026T-Syntax-bugs"></a>
<h4 class="subsection">9.15.16 AT&amp;T Syntax bugs</h4>

<p>The UnixWare assembler, and probably other AT&amp;T derived ix86 Unix
assemblers, generate floating point instructions with reversed source
and destination registers in certain cases.  Unfortunately, gcc and
possibly many other programs use this reversed syntax, so we&rsquo;re stuck
with it.
</p>
<p>For example
</p>
<div class="smallexample">
<pre class="smallexample">        fsub %st,%st(3)
</pre></div>
<p>results in &lsquo;<samp>%st(3)</samp>&rsquo; being updated to &lsquo;<samp>%st - %st(3)</samp>&rsquo; rather
than the expected &lsquo;<samp>%st(3) - %st</samp>&rsquo;.  This happens with all the
non-commutative arithmetic floating point operations with two register
operands where the source register is &lsquo;<samp>%st</samp>&rsquo; and the destination
register is &lsquo;<samp>%st(i)</samp>&rsquo;.
</p>


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