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.

Version	CCRL Blitz	CCRL 40/15	CCRL FRC	CEGT 40/4	CEGT 40/20
v1.10	2385	2347	*	*	*
v1.20	2509	2450	*	*	*
v1.30	2600	2594	*	*	*
v1.40	2697	2694	*	*	*
v1.50	2790	2772	*	*	*
v1.60	3043	3013	*	2872	*
v1.7x	3095	3049	2996	2929	*
v2.00	*	3285	3529	3194	*
v2.10	3392	3337	3599	3274	3253
v2.20	3468	3393	3685	3337	*
v2.30	3521	3427	3754	*	3372

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 It may be incomplete or outdated at times.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