Edwards' Tablebases

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Edwards' Tablebases, are three-, four and some five-piece tablebases constructed by Steven Edwards in the early 90s, initially for his chess program Spector. Edwards' Tablebases rely on Depth to Mate and the complete coverage for both sides, using one byte per position, with evaluations of the forms "mate in N", "lose (get mated) in N", "draw", and "illegal". Values for the number N (measured in fullmoves, not ply) for mates range from mate in 1 upto mate in 126 and for losses in 0 (lose in 0 means checkmated) to lose in 125 moves. Each file is for a given class (e.g., KBNK) and for a given side to move (e.g., White). After finishing the construction procedure in 1994, Steven Edwards made the whole data, documentation and a test program written in C|ANSI-C publicly available on the Internet. Until the advent of the compressed Nalimov Tablebases, Edwards' Tablebases were quite popular and used in several chess programs, such as Crafty, Gromit, and the commercial MChess Pro, to name a few.

=Index Scheme= The index scheme for pawn-less endgames exploits the fourfold symmetry of the chessboard to restrict the last identified piece to the a1-d1-d4 triangle by horizontal, vertical, or diagonal reflections, and features vertical symmetry by confining one pawn to the queen-side flank for endgames with one pawn. Other schemes as applied for instance in Thompson's Databases, enumerating all legal positions of both kings as combined index and considering pawns can't reside on the first or eighth rank, feature denser index ranges than Edwards'.

=See also=
 * Bitbases
 * Gaviota Tablebases
 * Lomonosov Tablebases
 * Nalimov Tablebases
 * Scorpio Bitbases
 * Syzygy Bases
 * Thompson's Databases

=Publications=
 * Steven Edwards and the Editorial Board (1995). An Examination of the Endgame KBNKN. ICCA Journal, Vol. 18, No. 3, pdf
 * Steven Edwards (1996). An Examination of the Endgame KBBKN. ICCA Journal, Vol. 19, No. 1

=Forum Posts=

1990 ...

 * Announcing forced mates: a poll by Steven J. Edwards, rgc, July 21, 1994
 * KBBK tablebases: attempt #2 by Steven J. Edwards, rgc, August 13, 1994
 * Updated tablebase documentation by Steven J. Edwards, rgc, October 14, 1994
 * KPK tablebases now available via ftp by Steven J. Edwards, rgc, October 14, 1994

1995 ...

 * Re: FICS vs. ICS: No, really, which is better? by Steven J. Edwards, alt.chess.ics, June 01, 1995
 * MCP6 Endgame Tablebase. Thanks mr.Hirsch! by H.Pieters, rgcc, November 11, 1996
 * Steve Edward's Endgame Tablebase generator is now available for WIN95 by Mike Byrne, CCC, November 01, 1997
 * EGTB by Frank Phillips, CCC, February 10, 1998

2000 ...

 * Tablebases Edwards by RR, Winboard Forum, July 25, 2001

2010 ...

 * A different tablebase encoding format by Steven Edwards, CCC, August 10, 2014

=Downloads=
 * [[File:tbgen.zip]]
 * [[File:Spector.zip]]

=References= Up one level