Texel 1.12

2025-01-05: Texel 1.12 (ELO: +85)

Neural network improvements:

• Speed up matrix multiplication for AVX-512.
• New network based on new training data.
• Use 4 "heads" (all NN layers except the first) for evaluation. The active head depends on the number of pieces on the board.
• Increase NN layer 1 output size from 256 to 384.

Tablebases:

• Measure thinking time more accurately. Useful when TB files are on mechanical disks.
• Better handling of DTZ scores in search.
• Avoid expensive (wrong side to move) DTZ probes in search.
• Add UCI parameter to control required search depth for DTZ probes.
• Measure time required to perform a TB probe instead of guessing. This avoids time losses in fast games when TB files are on mechanical disks.
• Allow RTB WDL probes in some cases even if hmc > 0.
• Change TB swindle depth from 16 to "15+minProbeDepth", to avoid slowdown in late middlegame/early endgame when TB files are on mechanical disks.

Search:

• Implement the counter move heuristic.
• Implement multi-cut pruning based on singular search score.
• Adjust singular extension search parameters.
• Allow both extension and reduction in the same search node.
• Remove no longer useful "recapture" and "going into pawn endgame" extensions.
• Reduce aspiration window size.

Other:

• Use multiple threads to initialize the transposition table.
• Better handling of mate scores in the transposition table.
• Fix handling of empty strings in UCI string options.

Texel 1.11

2024-01-12: Texel 1.11 (ELO: +63)

Neural network improvements:

• Fewer non-incremental updates of the first layer state.
• Implement quantization aware training.
• Better GPU utilization by using separate data loading threads.
• Efficiently handle training data that is too large to fit in RAM.
• Train a new network based on new training data evaluated by Texel 1.10.
• Optionally use AVX-512 instructions.

Other:

• Re-calibrate UCI_Elo for NNUE.
• Fix a null-move verification problem.
• Update GoogleTest code to version 1.14 to fix warnings when using new CMake versions.
• Add state to the Square class, i.e. make it contain the square number.

Texel 1.10

2023-09-25: Texel 1.10 (ELO: +173)

Speed up evaluation:

• More handwritten code using compiler intrinsics.
• Switch from gcc to clang for Windows compiles.
• Cache-line align data for more efficient SIMD load/store.
• Avoid "horizontal adds" in matrix multiplication by re-arranging weight data
  ahead of time.

Better neural network:

• Train a new network based on new training data evaluated by Texel 1.09.
• Use both search scores and game results when generating training data.
• Compute quantized validation error during training.
• Set unused layer 1 weights to 0 during training, to reduce compressed network
  size.
• Print weight/bias statistics during net quantization, to make it possible to
  see if quantization parameters are reasonable.
• Permute the quantized net for more efficient sparse handling of the outputs
  from the first layer.

Compilation fixes:

• Fix Visual Studio debug compilation.
• Fix cygwin/msys2 compilation problems.
• Better SIMD support for 32-bit CPUs.

Other:

• Add source code for "syncengine" program.
• Allow MultiPV mode also when playing games.
• Re-introduce evaluation score reduction when the half-move clock is large.
  No strength improvement but avoids shuffling moves in some situations.

Texel 1.09

2023-07-30: Texel 1.09 (ELO: +252)

• Implement NNUE evaluation.

Texel 1.08

2023-06-10: Texel 1.08

New features:

• Allow arbitrary hash table sizes up to 1TiB of memory.
• Add "contempt" UCI parameter.
• Add automatic contempt depending on opponent name.
• Add support for 7 man syzygy tablebases.
• Add "runcmd" Windows program. Useful for GUIs that don't allow specifying command line arguments to the engine.

Bug fixes:

• Fix crash in Windows NUMA/CPU discovery code.
• Fixed rare crash when running in cluster mode.
• Changed default "ponder" UCI option value to false.

Time management:

• More dynamic time management.
• Better time allocation for ponder on games.

Search:

• Use depth-dependent singular extension threshold.
• Add tempo bonus.

Reduced strength:

• Add MaxNPS UCI parameter.
• Make reduced strength work for Threads > 1.
• Add UCI_LimitStrength and UCI_Elo support, range -625 - 2540.

Infrastructure:

• Use CMake instead of a handwritten Makefile.
• Use Google Test framework instead of CUTE.

texelutil:

• Use C++ threads instead of OpenMP.
• Build texelutil with reduced functionality even if Armadillo and GSL libraries are not found.
• Add a reverse move generator, "texelutil revmoves".
• Improve "texelutil proofgame" for random positions.
• Add "texelutil rndfen" to generate random positions.

Documentation:

• Document how to estimate number of legal chess positions.
• Document the Texel tablebase probing algorithm.

Texel 1.07

2017-09-30: Texel 1.07 (ELO: +35)

Search:

• More aggressive LMR in expected CUT nodes.
• Don't use history and killer heuristics for captures.
• Prevent q-search explosion in pathological cases.
• Allow LMR for checking moves with negative SEE value.
• Don't do internal iterative deepening when in check.
• Don't do razoring when in check.
• Don't check extend SEE<0 moves at depth<=3.
• More LMR/LMP reduction if the evaluation score is worse than it was two plies
  ago. Idea from stockfish.
• More aggressive reverse futility parameters.
• In hash replacement, prefer a deep bound over a shallow exact entry if the
  depth difference is larger than 3.
• Use history score to control LMR reductions.

Parallel search:

• Parallel search algorithm changed to hybrid lazy SMP / ABDADA.
• Removed code that on NUMA avoids probing the TT at depth 0 for nodes > 0.

Evaluation:

• Removed the piece trade bonus.
• Implemented fortress detection for KQvsKRM+pawns endgames.
• Added endgame correction for KQKNNNN which is generally won by the knights.

Speed:

• Support for large and huge page allocations for the transposition table.
• Added alpha/beta pruning to the SEE function.
• Added support for sliding move generation using the PEXT BMI2 machine code
  instruction.

Other:

• Include "hashfull" information in UCI output.
• Added UCI option to control whether the transposition table is aged when
  starting a new search in analysis mode.

Texel 1.06

2016-07-10: Texel 1.06 (ELO: +56)

Search:

• Don't use ply-2 killers for move ordering.
• Be more restrictive when extending losing (SEE<0) checks.
• Don't do check extensions for moves that are reduced by LMR.
• Don't do singular extensions if the unextended score is a mate score.
• Don't do LMR for the first 2 pseudo-legal moves.
• More aggressive LMR.
• More aggressive null move searches.
• Don't resolve a known loss score bound if there are other moves that are
  potentially not losing.

Parallel search:

• Allow a helper thread that fails high to interrupt the master thread.
• Changed MIN_SPLIT_DEPTH from 10 to 7 to make better use of multiple threads in
  short time control games.
• Changed maximum number of search threads to 512.
• Added support for windows NUMA systems having more than 64 cores.

Evaluation:

• Evaluation term to encourage "pawn breaks".
• Bonus for "latent" pawn attacks on enemy minor and major pieces.
• Bonus for safe queen contact checks.
• Only treat pawns on rank 2 and 3 as backwards pawns.
• King safety bonus for pieces (except bishops) on the same side of the board as
  the king.
• Parameter tuning.

Endgame:

• More patterns for fortress detection in bishop endings.
• On-demand tablebase generation for 4-men pawn-less positions.
• Knowledge about KRKBNN endgame, which is generally a draw.
• Better evaluation of KRBNKRB endgame.
• Larger evaluation score in KRRMKRR endgames
• Improved 50 move draw handling for TB probes.

Speed:

• Reduced TB probe overhead.
• Implemented a small (512KB) per-thread evaluation hash table.
• Removed support for fractional depth.
• Made the transposition table 4-way set associative.

Other:

• Removed "64-bit" from the engine name. 64 bit is now considered standard.
• UCI option to disable null moves.
• Made "BufferTime" a UCI parameter to control time handling safety margin.
• Don't start a new search iteration if it is unlikely that it can finish before
  the allocated thinking time is up.
• In analysis mode, don't age transposition table entries when starting a new
  search.

Texel 1.05

2015-01-24: Texel 1.05 (ELO: +57)

• Added support for Gaviota and Syzygy tablebases.
• Improved the built in opening book.
• Implemented UCI option "Clear Hash".
• Optimization for NUMA hardware.
• Earlier transposition table prefetch.
• Added evaluation of "semi-trapped" rooks.
• Removed the guarded passed pawn evaluation.
• Don't rely on the transposition table to communicate search results from helper to master thread.
• Use more time early in sudden death and increment games.
• Smaller delta in aspiration window loop.
• Optimized history heuristic update formula.
• Improved fortress detection for bishop and pawns vs pawns.
• Detection of "16 pawn fortress positions".
• Added bonus for pieces protected by pawns.
• Fixed incorrect draw scores in multipv mode.
• Made piece square tables have left/right asymmetry.
• Detection of KQKRP fortress positions.
• Disabled LMP in PV nodes.
• Only do check extension for negative SEE moves if the remaining depth is small.
• Implemented singular extensions.
• More aggressive LMR.
• Fixed makefile to make multi-threaded search work for Android.

Texel 1.04

2014-05-29: Texel 1.04 (ELO: +72)

• Added separate queen piece square tables for middle game and endgame.
• Added recognition of some drawn endgames involving bishops and pawns.
• Added evaluation corrections for QvsRR, QvsRM, RvsM, RvsMM.
• Made bishop pair bonus depend on number of opponent minor pieces.
• Added more evaluation terms for pawns (own and opponent) in front of the king.
• Added evaluation terms for king assisting passed pawns.
• Made king endgame piece square table contain 32 parameters.
• Made the isolated and doubled pawn penalties file dependent.
• Added file dependent passed pawn bonus.
• Only use the protected passed pawn bonus when the non-pawn material is balanced.
• Improved knight mobility evaluation.
• Added bonus for a piece blocking an opponent passed pawn.
• Added non-linear king safety and tuned other king safety parameters.
• Improved KRKP evaluation.
• Added evaluation of connected passed pawns.
• Added drawishness factor to rook endgame evaluation, based on white/black pawn asymmetry.
• Added endgame corrections for KRPKM.
• Added square-dependent bonus for pawns protecting/attacking other pawns.
• Added bonus for minor pieces protecting the king.
• Added penalty for semi-backward pawns.
• Reduce evaluation score when the halfmove clock is large.
• Added bonus for rook behind passed pawn.
• Optimized razor margins and delta pruning margin using CLOP.
• Improved the built in opening book.

Texel 1.03

2014-01-19: Texel 1.03 (ELO: +112)

• Multi-threaded (SMP) search.
• Remove moves before the last zeroing move from the repetition history list before starting search.
• Removed bogus transposition table store in Search::iterativeDeepening().
• Disable aspiration window logic when searching for a faster mate.
• Added null move verification search.
• Prefetch entries from the main transposition table.
• Bonus for candidate passed pawns.
• Skip move ordering after enough moves to trigger LMP have been searched.
• Implemented pawn storm bonus for opposite castling positions.
• Removed the Botvinnik-Markoff extension.
• More aggressive LMR.
• Added knowledge for KBpKB, KNpKB, KBpKN and KNpK endgames.
• Store endgame flag in material hash table.
• Optimized lots of evaluation function parameters.
• More consistent evaluation of different classes of pawnless endgames. KQK, KRK, KQKM, KBBK, KBNK, KQKR, KQKMM, KMMKM (M = B or N).
• MultiPV-support.
• Mate distance pruning.
• Evaluation correction for 7 knights vs 3 queens.
• Display engine evaluation using "info string" when starting search in analysis mode.
• Changed internal parameter handling to make it easier to switch between UCI parameters and compile-time constants.