Misc/abrash-black-book
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James Gregory 2013-12-30 12:25:34 +11:00
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06-02.html
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@ -132,7 +132,7 @@ add ebx,edx
<P>and would in either case require the destruction of the contents of another register.
</P>
<P>Multiplying a 32-bit value by a non-power-of-two multiplier in just 2 cycles is a pretty neat trick, even though it works only on a 386 or 486.</P>
<TABLE WIDTH="100%"><TD WIDTH="5%" VALIGN="TOP"><IMG SRC="images/06-01i.jpg"><TD WIDTH="95%"><SMALL><I>The full list of values that <B>LEA</B> can multiply a register by on a 386 or 486 is: 2, 3, 4, 5, 8, and 9. That list doesn&#146;t include every multiplier you might want, but it covers some commonly used ones, and the performance is hard to beat.</I></SMALL>
<TABLE WIDTH="100%"><TD WIDTH="5%" VALIGN="TOP"><IMG SRC="images/i.jpg"><TD WIDTH="95%"><SMALL><I>The full list of values that <B>LEA</B> can multiply a register by on a 386 or 486 is: 2, 3, 4, 5, 8, and 9. That list doesn&#146;t include every multiplier you might want, but it covers some commonly used ones, and the performance is hard to beat.</I></SMALL>
</TABLE>
<P>I&#146;d like to extend my thanks to Duane Strong of Metagraphics for his help in brainstorming uses for the 386 version of <B>LEA</B> and for pointing out the complications of 486 instruction timings.</P><P><BR></P>
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