Author: Dieter Buerssner
Date: 04:43:51 12/24/03
Go up one level in this thread
On December 24, 2003 at 01:52:18, KarinsDad wrote: >Standard encoding for a position with no captures yet yields: > >62 bit piece/pawn location >12 bit kings and castling info >30 bits (max) piece or pawn >16 bits (max) pawn color >48 bits (max) piece type and color >1 bit side to move >3 bits e.p. (if necessary, the other e.p. bit isn't needed) > >So, we are at 172 bits max for the normal encoding. Capturing a pawn with >another pawn drops a pawn color bit and a piece/pawn bit, but there are now 3 >remaining pawns that could promote and change to pieces for a net gain of 4 more >bits (+6 - 2), etc. So already 176 bits for a general 31-men position, ..., 188 bits for 28 men (4 pawns captured, 12 promotions). In sight of this, the encoding of direct pieces looks more attractive. 30 pieces/pawns. 3 conveniently fit in 10 bit (10^^3 < 2^^10), so no long arithmetics is needed. We don't need the 30iest piece (there is only one legal material configuration with 32-men). Instead we could use it as ep column. 1 (stm) + 12 (KK/castling) + 62 (location) + 100 (pieces+ep) = 175 Perhaps an efficient enumeration would be possible, to save one bit for the location vector (less than half of all possible states are used, because a maximum of 30 bits are set). One could also save 2 bits for the ep. one ep-bit 3 for ep.column, one that means "there is an opponent pawn left of the ep-column", if not, there must be one right of it. There is no need to encode that pawn (also not in the location vector). Also, 2 squares behind the ep-pawn must be empty, which can be left out of the location vector. And then the pawn that just made a double step is neither needed in the location vector nor in the piece list. So we are down to 173 bits. (one ep bit instead of a bit more than 3). Perhaps one could find a method, to cleverly encode the ep-bit as an illegal position (only needed for 32 and 31 men). > There are ways to decrease this, but they are tricky. Are you refering to the problem with the promotions? Can you elaborate? Regards, Dieter
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.