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Topple

Topple is a UCI-compatible chess engine. Topple v0.7.5 is rated 3063 on CCRL 40/15 on 4 threads.

Download

Windows users should go to the Releases page, which hosts pre-built binaries. The modern binary should be preferred, but popcnt can be used for older systems. The legacy build does not use the popcount instruction and is slowest.

Compilation instructions for other platforms are available below.

Usage

Topple requires a GUI that supports the UCI protocol to be used comfortably, although it can be used from the command line.

A list of UCI-compatible chess interfaces is available on the Chess Programming Wiki.

Topple implements some extensions to the UCI protocol to make it easier to use from the command line.

  • eval returns a static evaluation of the position
  • print displays a textual representation of the board and previous moves
  • mirror flips the colours in the current position
  • position moves ... is stateful and can be used to continue an existing position
    • The UCI protocol normally requires each position command to specify all moves from a start position, e.g. position startpos moves e2e4 e7e5 g1f3 ...

Configuration

Five configuration options are made available: Hash, MoveOverhead, Threads, SyzygyPath and Ponder.

The Hash option sets the size of the main transposition table in MiB. If the size given is not a power of two, Topple will round it down to next lowest power of 2 to maximise probing efficiency. For example, if a value of 1000 is specified, Topple will only use a 512 MiB hash table. Hash does not control the value of the other tables in Topple, such as those used for move generation, evaluation and other data structures.

The MoveOverhead option sets the (network or GUI) delay that should be accounted for in time management. This can be used to prevent losses on time.

The Threads option sets the number of search threads that Topple will use. Topple may use additional threads for keeping track of inputs (such as the UCI stop command). Topple utilises additional threads by using Lazy SMP, so the Hash value should be increased to improve scaling with additional threads.

The SyzygyPath option sets the location in which Topple should search for Syzygy tablebases. These can be used to somewhat improve playing strength in the endgame. Multiple paths should be delimited by a semicolon on Windows and a colon on other operating systems.

The Ponder option has no effect, but is used to indicate that Topple has the ability to think during its opponent's time.

Compilation

Topple uses GCC extensions (e.g. __builtin_prefetch) and will need a GCC-compatible toolchain. Beyond that, the code is platform independent and has been tested on both x86 and ARM.

Install a toolchain and CMake (example commands given for Ubuntu):

sudo apt install build-essential cmake

Clone and build Topple:

git clone https://github.com/konsolas/ToppleChess
mkdir build
cd build
cmake ../ToppleChess
make Topple

Run unit tests: (optional)

make ToppleTest
ctest

Building a release: (optional)

cmake -DCMAKE_BUILD_TYPE=Release ../ToppleChess
make Release

The current Windows binaries are built with LLVM/clang.