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Subject: Re: typical nps on single cpus

Author: Dave Gomboc

Date: 23:03:28 02/14/00

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On February 15, 2000 at 01:53:43, Dan Newman wrote:

>On February 14, 2000 at 22:53:03, Dave Gomboc wrote:
>
>>On February 14, 2000 at 22:18:18, Dan Newman wrote:
>>
>>>On February 14, 2000 at 15:25:24, Dave Gomboc wrote:
>>>
>>>>On February 14, 2000 at 14:38:14, José de Jesús García Ruvalcaba wrote:
>>>>
>>>>>On February 14, 2000 at 03:16:33, Dave Gomboc wrote:
>>>>>
>>>>>[big snip]
>>>>>>
>>>>>>How much faster do you think a switch is than using virtual dispatch?
>>>>>>
>>>>>>Dave
>>>>>
>>>>>What is a virtual dispatch?
>>>>>José.
>>>>
>>>>What you get if you went OO-crazy and had a piece class with descendents for
>>>>pawn, knight, bishop, etc., then called a member function.
>>>>
>>>>Dave
>>>
>>>I've tried to go OO-crazy once or twice, but the one thing that seemed to
>>>get in the way and require some really hairy solution was pawn promotion.
>>>The only thing I could think of doing was to maintain a pool of extra
>>>promotion pieces and perhaps overload new and delete in the piece class to
>>>get the new piece from this pool.  But all that extra mechanism seemed like
>>>too much...
>>>
>>>-Dan.
>>
>>I'm not suggesting that going OO-crazy is a good idea (hence my name: OO-crazy
>>:-).  I'm just wondering how much longer do you think a virtual dispatch would
>>take than a standard switch statement.
>>
>>(Assuming there are no classes being loaded dynamically at run-time, there
>>doesn't seem to be a reason that it should be any slower at all, in this
>>particular case.  Do C++ compilers usually know that classes at the bottom of >an inheritance hierarchy are amenable to optimizations that would be unsafe on
>>classes that are higher up?)
>>
>>Dave
>
>Well, if you put the move generator into one function (and it does no function
>calls itself except those that are inlined) then you get the cost of one
>function call.

Okay.

>               But if you go the virtual function route, then you get a
>call for each piece.  I suppose the virtual function mechamism will cost a
>little extra too--maybe a couple of instructions.

You shouldn't get a function call for each piece -- that should all be inlined,
no?  I'm thinking that virtual dispatch in this situation should actually reduce
to a switch that is guaranteed to not have a default case -- thanks to the
wonders of static type checking.  Maybe I'm missing something.

Dave



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