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Subject: Re: C and C++ --- NPS

Author: Dave Gomboc

Date: 01:17:34 12/25/02

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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.

Please excuse my ignorance, but where is the branch?  It's an indirect jump,
isn't it?  There's nothing optional about it, it must be followed.  Is it that I
am not familiar enough with the terminology?  e.g. I am thinking that by "branch
prediction" you may be including any operation that moves the program counter in
any way other than advancing sequentially to the next instruction.

In any case, I'm confident that if you have a serious inheritance hierarchy (as
opposed to a toy example) you're not going to lose any sleep over the virtual
function call.  Many if-then-elses aren't efficient either.

Dave



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