Computer Chess Club Archives




Subject: Promotion frequency

Author: Russell Reagan

Date: 21:14:49 07/22/02

I am attempting to use an object-oriented approach in developing my engine, and
I have a problem and question about handling promotions.

My problem is that my object-oriented design prevents me from handling promotion
as efficiently as I'd like. I would like to handle it by storing the piece to
promote to in my move structure, then to promote it's simply a copy of the piece
type over the existing pawn type. Something like this:

squares[] = move.promotePiece;

That's nice and simple, and it probably doesn't get much faster. Using an
object-oriented approach, I have to do something like this:

if (move.isPromotion()) {
    if (move.isPromotionToQueen())
    else if (move.isPromotionToRook())
    else if // you get the idea

This isn't quite as simple, and not quite as fast, but it's not exactly huge or
complex either. I suppose that it's not a huge penalty since we usually promote
to queen anyway.

I really have two questions regarding this. Can anyone think of a better way to
handle this without the position class having to access the move class' private
data? I'd like to avoid those dependencies, since if I allow them that kind of
defeats the purpose of doing it object-oriented in the first place. Perhaps I'm
trying to force a non-OOP shape into the OOP shaped hole.

My second question is, is the case of promotion rare enough for this to not
really be an issue? I think it probably isn't, but I have nothing other than a
hunch to back that up. Then again, if promotion is there but it's still quite a
few plys away, the slightly less efficient method would increase that
inefficiency exponentially.

I also wonder if it even matters, since one side is about to promote and gain a
(usually) decisive advantage, it shouldn't matter if it slowed down horribly for
a breif time.

Any thoughts?


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