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Purple Haze

Do chess engines dream of electric guitar?

Synopsis

Purple Haze is a free chess engine compatible with the Xboard protocol. It is written by Vincent Ollivier and distributed under the terms of the GNU General Public License version 3.

The development of Purple Haze started in the winter of 2006-2007 as a pet project to learn the Java programming language by a student in Computer Science. It was terribly slow and rapidly put aside for two years before benefiting from a regained interest after much research and reading of papers on the subject.

A new version was written in C++11 between the summer of 2009 and the beginning of 2010 but it was full of bugs and not well engineered so a second major rewriting started during the winter of 2010-2011. This time it was only slightly faster but it would prove to be a lot easier to maintain and the overall code quality was enhanced by using a test-driven development practice. The goal is to end up with something reasonably good and free of bugs.

Most of its concepts or algorithms are inspired from scientific papers and Open Source engines, notably TSCP, CPW, Fruit, Crafty and Stockfish. A lot of the ideas used for the implementation of theses concepts also comes from reading the Computer Chess Club Forums and the Chess Programming Wiki. Without them Purple Haze would not be able to do more than moving the pieces around the board.

Installation

See INSTALL for detailed installation instructions or just type the following commands in a terminal:

$ git clone git://github.com/vinc/purplehaze.git
$ cd purplehaze
$ make

Features

Data Structures:

  • 0x88 Board Representation
  • Piece-Lists

Moves:

  • Lazy Move Generation
  • Best Move from Iterative Deepening or Transposition Table
  • Most Valuable Victim / Least Valuable Aggressor
  • Killer Moves

Search:

  • Principal Variation Search
  • Iterative Deepening
  • Transposition Table
  • Mate Pruning
  • Check Extension
  • Adaptive Null Move Pruning
  • Extended Futility Pruning
  • Late Move Reduction

Quiescence Search:

  • Standing Pat
  • Delta Pruning
  • Move Ordering (via MVV/LVA)

Evaluation:

  • Lazy Evaluation
  • Material Hash Table
  • Opening and Ending Piece-Square Tables
  • Tapered Evaluation

Debugging:

  • Perft
  • Divide
  • EPD Test Positions

Miscellaneous:

  • SAN output
  • FEN parsing
  • Zobrist hashing
  • Xboard protocol
  • Time Management

Usage

You are free to read it, run it and modify it. If you choose to do so, drop me an email at [email protected], it is not yet a mature project so any feedback will be really appreciated.