Misc/abrash-black-book
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Retidy, removing align=left from headings and empty paragraphs

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James Gregory 2013-12-30 15:37:13 +11:00
commit a96a114403
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
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<center>
<table border="1">
<tr>
<td><a href="17-02.html">Previous</a></td>
<td>
<a href="17-02.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="17-04.html">Next</a></td>
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<a href="17-04.html">Next</a>
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</center>
<p><br /></p>
<h3 id="Heading5">Where Does the Time Go?</h3>
<p>How slow is Listing 17.1? Table 17.1 shows that even on a 486, Listing 17.1 does fewer than three 96x96 generations per second. (The times in Table 17.1 are for 1,000 generations of a 96x96 cell map with <b>seed=1, LIMIT_18_HZ=0, WRAP_EDGES=1,</b> and <b>magnifier=2,</b> running on a 33 MHz 486.) Since my target is 18 generations per second with a 200x200 cellmap on a 20 MHz 386, Listing 17.1 is too slow by a rather wide margin&mdash;75 times too slow, in fact. You might say we have a little optimizing to do.</p>
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<p>Having said that, let me hasten to add that algorithmic improvements can make a big difference even when working at a purely abstract level. For a large unordered data set, a high-level Quicksort will beat the pants off the best-implemented insertion sort you can imagine. Still, you can optimize your algorithm from here &rsquo;til doomsday, and if you have a fast algorithm running on top of a highly abstract programming model, you&rsquo;ll almost certainly end up with a slow program. In Listing 17.1, the abstraction that&rsquo;s killing us is that of looking at the eight neighbors with eight completely independent operations, requiring eight calls to <b>cell_state()</b> and eight calculations of cell address and cell mask. In fact, given the nature of cell storage, the eight neighbors are in a fixed relationship to one another, and the addresses and masks of all eight can generally be found very easily via hard-wired offsets and shifts once the address and mask of any one is known.</p>
<p><br /></p>
<center>
<table border="1">
<tr>
<td><a href="17-02.html">Previous</a></td>
<td>
<a href="17-02.html">Previous</a>
</td>
<td><a href="index.html">Table of Contents</a></td>
<td>
<a href="index.html">Table of Contents</a>
</td>
<td><a href="17-04.html">Next</a></td>
<td>
<a href="17-04.html">Next</a>
</td>
</tr>
</table>
</center>