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<h4 class="section">Notes</h4>
<p>There is some trickery concerning the <code>mul</code> and <code>imul</code>
instructions that deserves mention. The 16-, 32-, 64- and 128-bit expanding
multiplies (base opcode <code>0xf6</code>; extension 4 for <code>mul</code> and 5
for <code>imul</code>) can be output only in the one operand form. Thus,
<code>imul %ebx, %eax</code> does <em>not</em> select the expanding multiply;
the expanding multiply would clobber the <code>%edx</code> register, and this
would confuse <code>gcc</code> output. Use <code>imul %ebx</code> to get the
64-bit product in <code>%edx:%eax</code>.
<p>We have added a two operand form of <code>imul</code> when the first operand
is an immediate mode expression and the second operand is a register.
This is just a shorthand, so that, multiplying <code>%eax</code> by 69, for
example, can be done with <code>imul $69, %eax</code> rather than <code>imul
$69, %eax, %eax</code>.
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