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Tantabus

Tantabus is a WIP hobby Chess and Chess960 engine.
It is a "rewrite" of Lunatic.
The code is restructured and a bit cleaner, and it also uses my own cozy-chess library in place of chess.
Play me on lichess: https://lichess.org/@/TantabusEngine.

Features

Movegen

  • Fixed shift fancy black magic bitboards using cozy-chess

Search

  • Principal variation search
  • Aspiration windows
  • Transposition table
    • "Always replace" replacement scheme
  • Quiescence search
  • Extensions
    • Check extensions
  • Reductions
    • Late move reductions
    • History reductions
    • Internal iterative reductions
  • Pruning
    • Null move pruning
    • Futility pruning
    • Reverse futility pruning
    • Late move pruning
    • Negative SEE moves pruned in QSearch
  • Move ordering
    • Hash move
    • Capture moves
      • Sorted with static exchange evaluation with capture history for tiebreaks
      • Losing captures delayed to last
    • Killer moves
    • History heuristic
  • Lazy SMP
    • Extremely simple implementation where the TT is shared among N search threads
    • Lockless transposition table implemented using relaxed atomics and the XOR trick
    • 4 threads measured as approximately 148 Elo stronger than 1 thread in 10,000 games

Evaluation

  • HCE
    • No longer exists, used to train NNUE
    • Automatically tuned with currently private tuner on the lichess-big3-resolved dataset
    • King relative symmetric piece-square tables
      • Dedicated passed pawn tables
    • Mobility evaluation (simple pseudo-legal counting)
    • Bishop pair bonus
    • Rook on open file bonus
    • Rook on semiopen file bonus
    • Basic king safety using "virtual queen mobility" and attacked squares around the king
    • Tapered/phased evaluation (using Fruit-like method)
  • NNUE
    • Simple (768 -> 128)x2 -> 1 network architecture
    • Data generated using custom program
    • Network trained using MarlinFlow
    • Two halves ordered by side to move and side not to move
    • Network quantized into integers for inference
    • Inference accelerated by custom SIMD code

Time management

  • Uses a fixed percentage of time left
  • Aborts after an iteration completes when a "soft limit" is exceeded
  • Aborts during an iteration when a "hard limit" is exceeded

Thanks

A (potentially incomplete) list of very useful resources:

Many engines have been very useful resources in the development of Tantabus.
A (potentially incomplete) list of citations is listed in the code, annotated with // CITE comments.
A (potentially incomplete) list of special thanks in no particular order:

  • Pali (Black Marlin author), for assisting me with various things during the development of Tantabus on top of being like, cool and stuff.
  • Jay (Berserk author) for having hosted the OpenBench instance that Tantabus developed on, as well as suggesting various improvements.
  • Andrew (OpenBench and Ethereal author) for OpenBench. OpenBench has been an immensely helpful tool for engine development. Ethereal is also a very influential engine.
  • MinusKelvin (Cold Clear and Frozenight author), for being like, really cool and stuff.
  • Anyone who donated CPU time to instance that hosts Tantabus.
  • Other people I probably forgot about.