Changelog

2017-07-30: Version 1.12 (Maven Port)

Don’t use aspiration window when mate score has been found.
Optimized the legal move generator. This has minimal effect on playing strength, but improves perft speed a lot.
Added bishop back rank penalty.
Don’t LMR reduce captures more than one ply.
Avoid array index out of bounds exception if the engine is asked to search a position where there are no legal moves.
Optimized piece values using CLOP.
Store razoring results in the transposition table.
Use SEE sign and MVV/LVA to order moves in non-q-search nodes.
Try equal captures before non-captures in non-q-search nodes.
Update killer moves when a transposition table hit gives a beta cutoff.
Implemented signSEE function that can be used when only the sign of SEE is needed.
Ignore squares attacked by enemy pawns when computing mobility.
Added evaluation of KRKP end games, based on statistics gathered from EGTB information.
Skip null-move search if the static score is below beta.
Update hash entry “generation” value after a transposition table hit.
Optimized bishop pair bonus using CLOP.
Optimized futility margins using CLOP.

Speeded up the SEE function by using bitboard techniques.
Use a lookup table to speed up castle bonus calculations.
Implemented specialized move generator function for check evasions.
Some speed optimizations.
Implemented specialized make/unmake move functions used by SEE.
Allow more time to resolve fail lows at the root.
Bug fix. Reset en passant square when making a null move.
Don’t allow too much time to resolve a fail low if too close to the next time control.
Stop searching immediately after a ponder hit if only one legal move.
Store successful null-move prunings in the transposition table.
Give extra bonus to passed pawns if enemy king is outside “the square”.
Only try two hash slots when inserting in the transposition table.
Try harder to keep PV nodes in the transposition table.
Use a hash table to speed up king safety evaluation.
Adjusted the knight piece square tables.
Added code to dump the search tree to a binary file, and code to browse and search the dump file.

Speed optimizations.
Only apply the “drawish factor” for opposite colored bishops if the non-pawn material is balanced.
Added evaluation of KQKP end games.
Added evaluation term for two rooks on the 7th rank.
Implemented delta pruning in the q-search.
Improved reduction logic. Don’t allow reduction of hash moves and killer moves, but allow larger reductions for other moves.
Fixed bug related to stalemate traps and the 50-move rule.
Allow null moves and LMR also in PV nodes.
Don’t do futility pruning and LMR for passed pawn pushes to the 6th and 7th ranks.
Added bonus in end games for having king close to opponents passed pawn promotions squares.
Don’t allow null moves when side to move doesn’t have pawns. This fixes problems in KQKR end games.
Extend the search one ply when going into a pawn end game.
Reduced queen mobility bonus.
Increased the passed pawn bonus and made it non-linear.
King safety adjustment.
Added a threat bonus evaluation term.
Penalize unmoved d/e pawns.
Undo LMR if the threat move slides through the LMR move “from square”. Idea from Stockfish.
Ponder even if there is only one valid move.
Allow LMR also at the root.

Speed optimizations.
Implemented non-linear mobility scores.
Fixed bad interaction of futility pruning/hashing/fail soft.
Tweaked rook piece square table a little.
Order root moves according to search tree size on previous ply.
Don’t trust mate scores from null move searches.
Increased the bishop pair bonus.
Tweaked king safety a bit.
Removed mate threat extension.
Only extend recaptures if the recapture is reasonable according to SEE.
Use a built-in bitbase for KPK evaluation.
Reduced the aspiration window to 25 centipawns.
Prune checking moves with negative SEE score in q-search.
Allow reductions and pruning of losing (according to SEE) captures.
Added end game evaluation of rook pawn and wrong-colored bishop.
Added penalty for rook trapped behind non-castled king.
Don’t allow double null moves.
Allow null move search to go directly into q-search.
More depth reduction in IID at large depths.
Implemented null move threat detection, to be able to undo unsafe LMR reductions. Idea from Stockfish.
Don’t overwrite a transposition table hash entry with inferior information for the same position. Could happen in IID.
Added evaluation of unstoppable passed pawns in pawn end games.
Include attacked squares close to the king in king safety evaluation.
Implemented magic bitboard move generator.
Use bitboard techniques for evaluation.
Created specialized move generator functions to generate checks.
Correctly handle pseudo-legal but not legal en passant squares.

Speed optimizations.
Avoid dynamic memory allocations during search.
Don’t do mate threat extensions too deep down in the search tree. Fixes search tree explosion in WAC 21.
Incremental update of material scores.
Created specialized move generator functions to generate captures.
Created a function givesCheck that decides if making a move gives check to the opponent.
Implemented a pawn hash table.
Store static evaluation scores in the transposition table.
If there is only one legal move at the root, make that move immediately.