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<h4 class="subsection">9.15.16 AT&T Syntax bugs</h4>
<p>The UnixWare assembler, and probably other AT&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're stuck
with it.
<p>For example
<pre class="smallexample"> fsub %st,%st(3)
</pre>
<p class="noindent">results in ‘<samp><span class="samp">%st(3)</span></samp>’ being updated to ‘<samp><span class="samp">%st - %st(3)</span></samp>’ rather
than the expected ‘<samp><span class="samp">%st(3) - %st</span></samp>’. This happens with all the
non-commutative arithmetic floating point operations with two register
operands where the source register is ‘<samp><span class="samp">%st</span></samp>’ and the destination
register is ‘<samp><span class="samp">%st(i)</span></samp>’.
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