General

• Disabled interprocedural optimisation for tests.

Search

• Adjusted parameters in the history heuristic.
• Removed alpha parameter from search_zw.
• LMR is now enabled for all moves, regardless of whether or not they are quiet.
• Even more aggressive LMR for quiet moves.
• Enabled recursive null move pruning.
• More aggressive razoring, null move pruning, and static null move pruning.
• Removed internal iterative deepening in zero window search.
• Bad captures are now pruned at low depths.

Evaluation

• Moved dynamic pawn evaluation from pawns.cpp to eval.cpp
• Fixed an asymmetry in king safety evaluation
• Rook and Bishop piece square tables now use 4-way symmetry instead of just 2-way symmetry.
• Replaced a bunch of repeated code with loops.
• Implemented evaluation of threats and undefended pieces.
• Decoupled game phase evaluation from material evaluation.

Estimated strength gain is around 30 elo based on self play.