Author: Ron Murawski
Date: 08:42:54 01/17/03
Current version is: Horizon 4.0 (release date: January 17, 2003) The estimated strength increase over the previous version is about 25 points in Blitz. The search is 25% faster early in a game and up to four times faster in the endgame. Pawn hashing has forced a complete rewrite of the evaluator. With the advent of pawn hashing, pawn play has improved noticeably. Candidate passed pawn recognition and scoring was totally rewritten. King safety shuts off sooner and the engine is encouraged to move the king to the center sooner. Several bug-fix corrections were made as well. This version isn't quite as pressing in its king attacks compared to past versions; Pawn considerations are contributing to choosing the best move. Important: There is now a pawn hash table. To set a 4 MB pawn hash table, alter Horizon.cfg to the following: PAWNHASH 4 All previous advice as to "ideal" main hash table size has been retracted. Use as large a hash as practical. See instruct.txt for more information. Tech Note: 2003/01/17 version 4.0: Pawn hashing implemented and pawn evaluation code totally rewritten. Candidate passed pawn recognition/scoring totally revamped. Optimizations for faster search. Forcing hash move first in quiescent move ordering. King safety shuts off sooner and king-to-the-center bonuses start sooner as well. Rebalanced the values of 8th rank blockade penalties. Moved all initialization code into the initialization section. Tweaked time control code to think longer just after leaving the book. Book-reader and some WinBoard messaging improvements. Bugfixes: 1) In positions with more than 128 legal moves, memory was getting overwritten. Increased legal move limit to 192; 2) Trojan attack code was wrong for Black bishops; 3) White 7th rank pawns with opposing pieces in front of them were scored incorrectly; 4) Early queen penalty was wrong and could cause a crash under certain circumstances. http://www.horizonchess.com/
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