Author: Gareth McCaughan
Date: 15:10:20 04/22/02
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On April 21, 2002 at 21:22:53, Russell Reagan wrote: > My specific question is about whether it's faster to use a struct > for your position, or to simply have some global variables. > Global variables seem like they would be faster because you > don't have to dereference the pointer. 1. All the people who have said that this is too small a difference to worry about, are absolutely right. 2. Global variables might be faster because you might save a pointer dereference. On the other hand, it'll be in cache all the time and shouldn't cost much. And if the pointer is in a register then you might have the same number of memory references either way. And global variables might be slower because constructing the address to look up might take a few instructions. All of these are small issues. 3. Global variables will make your program harder to parallelize. Don't worry about this. There are so many *real* difficulties with making a decent parallel program (the search, the hash tables, etc) that this sort of superficial thing will be lost in the noise. 4. When you have any optimization issue, there are three rules about optimizing code. a. "Jackson's First Rule": Don't do it. b. "Jackson's Second Rule" (for experts only): Don't do it yet. c. Profile your code. Measure, don't guess. -- g
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