Author: Ulrich Tuerke
Date: 09:45:43 05/18/03
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On May 18, 2003 at 11:48:40, Robert Hyatt wrote: >On May 17, 2003 at 14:35:43, Ulrich Tuerke wrote: > >>> >>>BTW. I started to change for one counter as an experiment (the normal node >>>counter), and used unsigned long long and double. The funny result: with both >>>methods, the program ran reproducably 0.5% faster ... >>> >>Are you telling when replacing "unsigned long" for the type of the node-count >>variable by "long long" or "double", then your program would run faster ? >> >>I guess, I got this wrong. Did I, Dieter ? >> >>Uli > > >This sometimes happens. Because of some serendipity thrown into the equation >by additional instructions needed to handle the extra 32 bits + the carry >operation. It is not uncommon to simply move a piece of code around and notice >a change in speed (sometimes faster, sometimes slower). This seems to be true. Nevertheless, I am a bit surprised in this case. Switching to 64 bit variables probably means that extra code will be required on assembler level (because of the 32 bit word size). So, it's not just "moving a piece of code around" but having additional code (as you have already mentioned). It seems more difficult on modern architectures to predict the influence of a code change on performance - perhaps because of thinks like pipelining, done by the processors. Uli
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