peacekeeper

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Peacekeeper

Solitudinem faciunt, pacem appellant
They make a desert and call it peace
- Tacitus

A strong UCI Chess Engine written in C++17.

Achieved top 100 in CCRL Blitz and CCRL 40/15 with hand crafted evaluation (HCE).

Download / Compilation

Peacekeeper can be compiled from source with GNU C++ or Clang with g++ -Ofast -DNDEBUG -march=native -o peacekeeper src/*.cpp MSVC intrinsics are supported as well as C++20 bit intrinsics, so the engine can in theory be compiled on a large range of compilers.

Windows (and formerly linux) executables are provided to download for each release in the Releases section.

Ratings

* denotes a version which has not been tested on that rating list and does not have a rating.

Ratings prefixed with ~ have large error margins because of few games played.

Note that ratings from different rating lists are not comparable to each other.

Issues

Issues on github can be created for any bugs, other issues found, or questions.

Features

This is a list of features I have implemented so far in Peacekeeper. It may be incomplete or outdated at times.

• Board Representation and Move Generation
  • Bitboard-based
  • Redundant Mailbox Board
  • Make-Unmake
  • Fixed-shift Fancy Magic Bitboards for slider move generation
  • Fully legal move generation
  • Supports Fischer Random Chess (FRC) and Double Fischer Random Chess (DFRC)
• Search
  • Supports LazySMP, can use up to 256 threads in parallel
  • Negamax framework
  • Principal Variation Search (PVS)
  • Quiescence Search (QS)
    • QS SEE Pruning
  • Iterative Deepening
    • Aspiration Windows
  • Staged Move Generation
    • Hash move
    • Captures
    • Quiets
  • Time Management
    • Soft and Hard Bounds
    • More time for unstable bestmoves
  • Transposition Table
    • Incrementally updated Zobrist hash
    • Used in both QS and PVS
  • Selectivity
    • Check Extensions
    • Static Null Move Pruning/Reverse Futility Pruning (SNMP/RFP)
    • Null Move Pruning (NMP)
    • Late Move Reductions (LMR)
    • Late Move Pruning (LMP)
    • Futility Pruning
    • SEE Pruning
    • Internal Iterative Reductions (IIR)
  • Move Ordering
    • MVV-LVA for captures
    • Killer Heuristic
    • History Heuristic for quiet moves
    • Continuation and Countermoves History
• Evaluation
  • Efficiently Updatable Neural Network (NNUE)
    • Used in version 2.00 and after
    • Tuned using modified version of Slender's Carbon trainer
    • 768->512x2->1 architecture
      • Clipped ReLU (CReLU) activation function
      • Perspective network
    • Trained on selfplay DFRC data
  • Hand-Crafted
    • Used in version 1.71 and before
    • Texel Tuned using Gradient Descent tuner
      • ADAM algorithm
    • King-Relative Piece Square Tables
    • Pawn structure
      • Passed Pawns
      • Free Passed Pawns
      • Doubled Pawns
      • Isolated Pawns
      • Supported Pawns
      • Pawn Phalanxes
    • Mobility
      • Regular mobility
      • Forward mobility
    • Bishop Pair
    • Open and Semi-Open Files
    • Tapered Eval
    • Tempo Bonus
      • Phase dependent
    • Contempt
      • Phase dependent

Credits & Thanks

In no particular order.

• Pradu Kannan for magic multipliers
• CPW (and Sungorus) for zobrist hash pseudorandom number generator
• The Chess Programming Wiki for being a great resource for everything related to chess programming
• The Talkchess forum and the people on it for answering my more specific questions
• The Engine Programming Discord and the people on it
• Slender (@rafid-dev) especially for coinhabiting an OpenBench instance, contributing hardware mutually, and sharing SSS test results
• @Witek902 for tons of hardware and hosting an OpenBench instance, and @gab8192
• Andrew Zhuo (@StackFish5) for constantly looking over my code
• @albert-wastakentoomuch, @ccao25 for help in generating data
• PeSTO for starter piece square tables
• Desmos for making the logo (lol)
• Chess cache (Dusan Stamenkovic) and Graham from CCRL for other logos that you can use
• Some engines which I got inspiration from (in alphabetical order) along with their authors:
  • Altair
  • Blunder
  • Leorik
  • Midnight
  • Pedantic
  • Polaris
  • Rice
  • Stockfish
  • Sunfish
  • Willow
• Rating list testers for testing my engine