Author: KarinsDad
Date: 21:13:18 05/17/99
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On May 17, 1999 at 23:08:33, Dann Corbit wrote: >On May 17, 1999 at 22:56:18, KarinsDad wrote: >[snip] >>This 174 does not include promotions. >> >>Actually, the 174 bits in the other posts came from a different scheme: >> >>100 bits 30 pieces and pawns packed >>12 bits kings and castling >>61 bits (62 remaining squares bitboard - last one not needed) >>1 bit side to move >> >>or something to this affect (but I do not know where ep fits into this, maybe >>into the kings structure). > >OK, stupid question time: > >Why do we need to store promotions for a position? After all, who cares how I >got there. And if the piece information must be retrieved from this format, I >could just consider the delta between this position and the previous one. > >There seems to be something major that I am missing here... Dann, I guess it depends on what you are using the structure for. If you are using the schema in your previous post Dann (virtually identical to the schema in my other post), then it does not keep track of promotions beyond the number of original pieces. For example, you could in a game not take any pieces, have 4 pawns on the board taken, and promote the remaining 12 pawns (not that this would exactly happen in a real game). Well, this would take an up an additional 16 or so bits, depending on the piece type (queens are 6 bits, other pieces are 5, pawns are only 3 bits, about 2 more bytes than is in the structure). The schema above (in this post) does keep track of promotions since it keeps track of all piece types where a pawn has the same number of bits as any other piece (with the exception of the kings). So, it doesn't matter if you have a pawn in the structure or a piece, they are the same size, so promotions are handled automatically. Now, if you are using the structure for a position which could be based on an opening book transformation, you would not necessarily know the previous move (you may, you may not, depending of how you are using it). If you used the structure from position to position, you would have state information that the structure does not save (such as the 50 move rule or draw by repetition). I did not know why you posted your original message on this, so I did not know why you wanted to use it. KarinsDad :)
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