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Subject: Re: C or C++ for Chess Programming?

Author: Larry Griffiths

Date: 17:22:08 08/21/00

Go up one level in this thread

On August 20, 2000 at 06:54:22, Dan Newman wrote:

>On August 19, 2000 at 09:39:02, Larry Griffiths wrote:
>>On August 19, 2000 at 05:17:56, Dan Newman wrote:
>>>On August 18, 2000 at 20:13:23, Dann Corbit wrote:
>>>>On August 18, 2000 at 05:07:09, Dan Newman wrote:
>>>>>OTOH, I have occasionally considered attempting a full blown OPP chess
>>>>>program complete with pools of chess pieces with overloaded new so that
>>>>>(for instance) on pawn promotion I could delete the pawn and new a queen...
>>>>Dumb as a box o' rocks observation:
>>>>Since the absolute "max" of posible chessmen is known, why hot just preallocate
>>>>a "box" of chess pieces with enough spares for either side.  Captured
>>>>pieces/pawns go into the box and promoted pieces are pulled from it.
>>>>At the start of a game, it contains:
>>>>White rooks: 8
>>>>White knights: 8
>>>>White bishops: 8
>>>>White queens: 8
>>>>White pawns: 0
>>>>No White king slot
>>>>Black rooks: 8
>>>>Black knights: 8
>>>>Black bishops: 8
>>>>Black queens: 8
>>>>Black pawns: 0
>>>>No Black king slot
>>>>If you wanted to carry the metaphor further, you could have all the starting
>>>>chess men in the box to start with and construct the board by pulling pieces and
>>>>pawns out of the box.
>>>>Each piece could have a bit that means in use/in box to use for error checking.
>>>>Sounds like bizarre overkill, perhaps.  But if your evaluation removes hundreds
>>>>of pieces or promotes hundreds of pieces during a search, it might be useful to
>>>>do it that way.
>>>This is more or less what I had in mind with the pool idea.  When, frex,
>>>"new WhiteQueen" gets executed, the overloaded new would find an unused
>>>white queen and return a pointer to it.  This would be a lot faster than
>>>going through the memory allocator...
>>>A neat thing about this scheme (of making a class for each piece type) is
>>>that you can put the move generator code into those classes and then simply
>>>iterate through the piece lists calling the virtual move generator functions
>>>to generate the moves.  OTOH, this is also going to add a lot of function
>>>call overhead to the program.
>>>If you are doing bitboards though, this isn't really an option.  Instead of
>>>pieces being relatively heavyweight objects, they are grouped together in
>>>bitboards by type...
>>>I think it may be a mistake (when deciding what classes are needed to do a
>>>chess progam in C++) to identify the physical objects involved in the game
>>>and make classes for them.  (That's the first thing I thought of when first
>>>attempting this a few years back.  The first two sorts of object I though of
>>>were the pieces and the board.  Beyond that what else is there?
>>>I quickly decided *that* was a mistake when I didn't see an easy way to turn
>>>pawns into queens.)  Instead (I think) you really need to look at what
>>>"things" are needed to play the game (like search, eval, moves, state info,
>>>etc.) and encapsulate those things instead--when it makes sense to do so.
>>>In my current chess program I've only haphazardly OOP'ed stuff in a few
>>>places where it helped.  For instance, my move is a class, and I get at its
>>>from and to-square coords via member functions so that I can experiment
>>>with move representation without having to do massive changes to the code.
>>>But for the most part I just use C++ as a "better" C.
>>Hi Dan,
>>My programs has a base class Piece and all my pieces are derived from it.  The
>>move genereate, makemove, and unmake move are also in the piece class along with
>>updating my bitboards.  I have a piece pool manager to get pieces and assigning
>>them to the board.  Pawn promotion flags the pawn in the piece list as inactive
>>and gets a queen from the piece pool when it gets promoted.
>>My program is just as fast as it always was when I did not do it this way.
>That's interesting.  It sounds like you have a sort of hybrid program, if
>you have bitboards *and* separate pieces in piece lists.  Actually, I guess
>I have pieces too (in a way) since I have a "board" array with byte sized
>entries which store the piece type and color--much as Crafty has.  But I
>don't have piece lists now that I use bitboards...  In fact that's the main
>reason I like bitboards; I always found piece lists problematical :).

I keep a list of black pieces and a list of white pieces.  When a ply has to
generate moves for the pieces, it loops thru the piece list.  I guess this was
the quickest way to generate moves without scanning thru the entire boards
squares looking for black pieces.

for(int i=0;i<blackpiecelist->Count;i++)
      {  // The piece is not captured (or promoted)

When a piece is captured or a pawn is promoted, then its state is set to
CAPTURED.  (probably should have used MIA or something instead of CAPTURED :)

>I've always wondered where make()/unmake() ought to go in an object oriented
>program.  I think I'd have a move class and that's where they'd go, but then
>how do you give the move's member functions access to all the state data
>that they need: 1) pass the board and so forth into make(), 2) have the
>board (and other state) be static members of the move class, or 3) make the
>board, etc., global?  Each choice seems to have its drawbacks.  1) makes
>the code cost more cycles that it needs to, 2) begs the question as to how
>other parts of the code are to get to the board, 3) seems to be contrary
>to the OOP paradigm...  I think 1) is probably the best choice.  Just
>pass a pointer to the state data into make().  I guess you end up having
>to do something like this anyway if you want to have a parallel search...

Very good questions Dan :)   My pieces have an OwnerBoard field in case it needs
to access something in the board class.  My Make/UnMake call is in my SearchTree
method which is part of my Board class. It calls the Make/UnMake in my Piece
class.  I am still moving the methods and objects around to see where they fit
best.  I also have a lot of globals (bitboards, squares etc.) that need to go
somewhere.  I really need to get rid of all my globals so that I could do some
parallel tasking with my SMP pc.

I do agree that there is some loss of performance when I have to start pointer
chains like Board->Piecelist->State etc.  I currently have inline assembler with
MMX and the pointer chains make the assembler sections harder to code.

I am try to keep the data closest to the objects that use them the most so that
I do not have long chains of pointers.

I still have a long way to go, but it has made the code so much simpler compared
to my previous chess program.


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