Author: Gerd Isenberg
Date: 17:33:34 12/24/02
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On December 23, 2002 at 21:33:50, Matt Taylor wrote: >On December 23, 2002 at 21:29:08, Arshad F. Syed wrote: > >>Is there anyone here who has actually converted their C code to C++ while >>keeping the NPS the same or even managed to improve upon it? Sune did mention >>that he did so only at the cost of 15% degradation in speed. Why do people even >>bother wasting their time with C++ for a chess program when it inevitably leads >>to taking a hit in NPS? Regardless, of all the advice to simply inline the >>functions, I have yet to see a living example of chess program code which >>performed faster in C++. >> >>Regards, >>Arshad > >The biggest hit you take in C++ is virtual functions, and inevitably people use >them. The virtual functions are very damaging due to the fact that they're >implemented with a function pointer, and at the machine level it translates into >an indirect call. The indirect calls branch mispredict because the CPU can't >figure out ahead-of-time where you're calling to, and branch mispredicts are >expensive. Hi Matt, really? The vtable index of a virtual function is a compile time constant. Is an indirect call via register a mispredicted branch per se, even if the register was loaded with this->vptr->someVfunctionPointer an appropriate time before the indirect call occurs? What branch could be executed, other than the determined indirect call? > >Unfortunately, not using virtual functions (mostly) defeats the benefits you >would get from OO here. > >If you convert to C++ without using virtual functions, you probably won't take >much of a hit at all. Personally, I've never seen a -need- to convert to C++. I >can implement my OO in C, and it simplifies linking because C doesn't have name >mangling. But polymorphism is nice to have, even without virtual functions. I don't believe that name mangling affects the linker a lot ;-) Regards, Gerd > >-Matt
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