Misc/abrash-black-book
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James Gregory 2013-12-30 12:25:34 +11:00
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@ -109,7 +109,7 @@ main(int argc, char *argv[]) {
</PRE>
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<P>Table 1.1 shows the time taken for Listing 1.1 to generate a checksum of the WordPerfect version 4.2 thesaurus file, TH.WP (362,293 bytes in size), on a 10 MHz AT machine of no special parentage. Execution times are given for Listing 1.1 compiled with Borland and Microsoft compilers, with optimization both on and off; all four times are pretty much the same, however, and all are much too slow to be acceptable. Listing 1.1 requires over two and one-half minutes to checksum <I>one</I> file!</P>
<TABLE WIDTH="100%"><TD WIDTH="5%" VALIGN="TOP"><IMG SRC="images/01-02i.jpg"><TD WIDTH="95%"><SMALL><I>Listings 1.2 and 1.3 form the C/assembly equivalent to Listing 1.1, and Listings 1.6 and 1.7 form the C/assembly equivalent to Listing 1.5.</I></SMALL>
<TABLE WIDTH="100%"><TD WIDTH="5%" VALIGN="TOP"><IMG SRC="images/i.jpg"><TD WIDTH="95%"><SMALL><I>Listings 1.2 and 1.3 form the C/assembly equivalent to Listing 1.1, and Listings 1.6 and 1.7 form the C/assembly equivalent to Listing 1.5.</I></SMALL>
</TABLE>
<P>These results make it clear that it&#146;s folly to rely on your compiler&#146;s optimization to make your programs fast. Listing 1.1 is simply poorly designed, and no amount of compiler optimization will compensate for that failing. To drive home the point, conListings 1.2 and 1.3, which together are equivalent to Listing 1.1 except that the entire checksum loop is written in tight assembly code. The assembly language implementation is indeed faster than any of the C versions, as shown in Table 1.1, but it&#146;s less than 10 percent faster, and it&#146;s still unacceptably slow.
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