Misc/abrash-black-book
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James Gregory 2013-12-30 12:25:34 +11:00
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@ -38,7 +38,7 @@
<P><BR></P>
<P>And indeed it does. When the test program is modified to draw to a local buffer, both the C and assembly language versions get 0.29 seconds faster, that being a measure of the time taken by display memory wait states. With those wait states factored out, the assembly language version of <B>DrawHorizontalLineList</B> becomes almost three times as fast as the C code.</P>
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<TD WIDTH="5%" ALIGN="LEFT" VALIGN="TOP"><IMG SRC="images/39-02i.jpg"><TD WIDTH="90%" VALIGN="TOP" ALIGN="LEFT"><SMALL><I>There is a lesson here. An optimization has no fixed payoff; its value fluctuates according to the context in which it is used. There&#146;s relatively little benefit to further optimizing code that already spends half its time waiting for display memory; no matter how good your optimizations, you&#146;ll get only a two-times speedup at best, and generally much less than that. There is, on the other hand, potential for tremendous improvement when drawing to system memory, so if that&#146;s where most of your drawing will occur, optimizations such as Listing 39.3 are well worth the effort.</I></SMALL>
<TD WIDTH="5%" ALIGN="LEFT" VALIGN="TOP"><IMG SRC="images/i.jpg"><TD WIDTH="90%" VALIGN="TOP" ALIGN="LEFT"><SMALL><I>There is a lesson here. An optimization has no fixed payoff; its value fluctuates according to the context in which it is used. There&#146;s relatively little benefit to further optimizing code that already spends half its time waiting for display memory; no matter how good your optimizations, you&#146;ll get only a two-times speedup at best, and generally much less than that. There is, on the other hand, potential for tremendous improvement when drawing to system memory, so if that&#146;s where most of your drawing will occur, optimizations such as Listing 39.3 are well worth the effort.</I></SMALL>
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<TD VALIGN="TOP" ALIGN="LEFT"><SMALL><I>Know the environments in which your code will run, and know where the cycles go in those environments.</I></SMALL>