Author: Andrew Dados
Date: 08:36:18 05/15/99
Go up one level in this thread
On May 15, 1999 at 10:20:48, KarinsDad wrote:
>Well, got some sleep. Figured out that I was wrong.
>
>The 168 bit maximum (175 bit maxium with 50 move rule) is not really the
>maximum.
>
>For example, white could have a pawn on f3, g4, and h4. Black could have a pawn
>on f4, g5, and h5.
>
>White could play hg. Black could then unopposed promote his h pawn with h4.
>White could now unopposed promote both of his g pawns. So, the worse case
>scenario is 12 promotions (no pawns left) and every original piece still on the
>board. All pieces would have to be on the 2nd to 7th rows and so we have gained
>2 bits per promotion or 24 bits, 3 whole bytes. A nightmare position to be sure.
>
>And unlike the position I set up here, a lot of the pawn promotions in a scheme
>of 12 promotions would not be unopposed.
>
>Now since we gain at most 2 bits per promotion, I doubt that there has every
>been such a situation where EVERY other piece is still on the board and pawns
>were in a configuration anywhere on the board such as the one I discribed
>without the pawn promotions being stopped by the other pieces (or pawns).
>
>So, this is fantasy positions. However, a purist WILL say, "Hey, you screwed up,
>I can set up a LEGAL position that your format will not support" (although not
>one that would ever show up in a game). However, I'm not sure it is worth it to
>worry about it.
>
>Opinions?
>
>KarinsDad :)
>
>PS. I also figured out something else important to this discussion, but I forgot
>it when I fell asleep. I hate when that happens.
Ok.. let's summarize.. Your format ends up with 22 bytes and does not
support all legal positions.. Now let's check way easier schema:
64 bits locations = 8 bytes
32x4 bits piece+color flag =16 bytes
50 move + ep+ castling rights+ side to move = 2 bytes
total gets to 26 but *any* 32 piece position is supported and way easier/faster
to code..
As usual - trade off....
-regards -
Andrew
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