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James Gregory 2013-12-30 12:25:34 +11:00
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@ -170,7 +170,7 @@ SearchMaxLengthendp
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<P>How much difference? Listing 7.2 runs in 121 &#181;s&#151;40 percent faster than Listing 7.1, even though Listing 7.2 still uses <B>LOOP</B> rather than <B>DEC CX/JNZ.</B> (The loop in Listing 7.2 could be unrolled further, too; it&#146;s just a question of how much more memory you want to trade for ever-decreasing performance benefits.) That&#146;s typical of local optimization; it won&#146;t often yield the order-of-magnitude improvements that algorithmic improvements can produce, but it can get you a critical 50 percent or 100 percent improvement when you&#146;ve exhausted all other avenues.</P>
<TABLE WIDTH="100%"><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="5%"><IMG SRC="images/07-05i.jpg"><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="95%"><SMALL><I>The point is simply this: You can gain far more by stepping back a bit and thinking of the fastest overall way for the CPU to perform a task than you can by saving a cycle here or there using different instructions. Try to think at the level of sequences of instructions rather than individual instructions, and learn to treat x86 instructions as building blocks with unique characteristics rather than as instructions dedicated to specific tasks.</I></SMALL>
<TABLE WIDTH="100%"><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="5%"><IMG SRC="images/i.jpg"><TD ALIGN="LEFT" VALIGN="TOP" WIDTH="95%"><SMALL><I>The point is simply this: You can gain far more by stepping back a bit and thinking of the fastest overall way for the CPU to perform a task than you can by saving a cycle here or there using different instructions. Try to think at the level of sequences of instructions rather than individual instructions, and learn to treat x86 instructions as building blocks with unique characteristics rather than as instructions dedicated to specific tasks.</I></SMALL>
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