Author: jonathan Baxter
Date: 20:47:15 06/13/98
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On June 13, 1998 at 10:13:55, Steven J. Edwards wrote: >On June 13, 1998 at 02:05:23, jonathan Baxter wrote: > >>Does anyone have a short description of the format of the tablbase >>files distributed with crafty? I have looked in the code but that >>part is pretty horrendous to read. > >That bad, eh? > >The values stored, one per byte, in a tablebase file are documented in >the epddefs.h file and give the mate-N, loss-in-N, etc. position >valuations. > >Each TB file is indexed by N subscripts where N is the number of men in >the class. The subscripts are applied in reverse name order; the white >king subscript varies fastest (its the first piece in the class name), >with each successive piece varying less fast. > >There are three flavors of subscripts: full, half, and triangle. > >The full flavor runs from 0 to 63 following the squares a1 to h8 and it >is the default flavor. (a1 b1 c1 d1 e1 f1 g1 h1 a2 b2 ... g8 h8) > >The second flavor runs from 0 to 31 following the squares on the >queenside. >(a1 b1 c1 d1 a2 b2 ... c8 d8). > >The third flavor runs from 0 to 10 following the squares a1 b1 c1 d1 b2 >c2 d2 c3 d3 d4. > >The rules are: > >1) In an N man class, exactly (N - 1) subscripts are full flavor. > >2) If there is at least own pawn in the class, then the last pawn in the >class name uses the second (32 square) flavor subscript > >3) If there are no pawns in the class, then the very last man in the >class name uses the third (triangle 10 square) flavor subscript. > >A position is folded via one or more of X, Y, and x=y rotations until >the non-default flavor subscript man is in the restricted (32 or 10) >square field. Do you mean *reflections* rather than rotations? >The index is comuputed and forms the file offset for the byte of >interest. > >Now that you know this, then maybe the code won't seem so bad. Thanks! Its a big help. If you are interested, I am trying to train an evaluation function directly using the tablebases. Jon > >-- Steven (sje@mv.mv.com)
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