Orion UCI chess engine

Download Orion (64-bit version)

April 3, 2016

Orion v0.3 is now available !

I'm very happy to release this new version after several weeks of hard work. It (almost) consists in a complete rewrite of the previous version, in order to have a more readable and robust code, which should be a better basis for further enhancements. And code is not throwing anymore tons of warnings when compiling ;-)

Aside from rewriting, some features have been added, changed or suppressed :
  • Added : Late move pruning
  • Added : Reverse futility pruning
  • Changed : Smarter time management
  • Suppressed : Incremental move generation
  • Suppressed : Hash storage and usage in quiescence search
  • Suppressed : Automatic detection of the x86-64 'popcnt' instruction support by the host CPU
Evaluation is unchanged. The new pruning techniques allow smaller search trees while adding some search instability. It results in less reliable moves in shallow depths, but should increase strength for longer time controls. I'm very impatient to see how it will behave in tournaments !

Next version will focus on evaluation enhancement with a PBIL framework already implemented and ready to be played with !

July 19, 2014

New Orion v0.2 ratings :

SiteTC (*)RankEloGames
(*) Time control (40/4 means 40 moves in 4 minutes)

June 25, 2014

Orion v0.2 participated in its first tournament ("Special Stars", organized by CCRL team) and finished in 4th place !

As it was my goal to compete with other engines, I'm very proud of it ;-)

June 17, 2014

First feedback from testers with computers that don't support 'popcnt' instruction show that the engine may crash : this problem has been fixed and a patched version of Orion v0.2 has been repackaged in the zip file (see download section).

This shows that we never test enough ! Thanks to all testers for their patience...

Please report any new problem here.

June 15, 2014

I'm pleased to announce the release of Orion v0.2 !

This new version includes :
  • Incremental move generation
  • Killers heuristic (to avoid quiet move generation)
  • Hash storage and usage in quiescence search
  • Delta pruning and See pruning in quiescence search
  • KPK evaluation improved (pawn is now considered as passed)
  • Automatic detection of the x86-64 'popcnt' instruction support by the host CPU (successfully tested on Core i5 & i7, hope it will work on other platforms) : in case of problem, launch "Orion.exe -no-popcnt" to disable it
All these features should improve the engine speed :-)

Please enjoy !

June 7, 2014

The CEGT team tested intensively Orion v0.1... playing 1100 games ! Here is the rating obtained :

TC (*)RankEloGames
(*) Time control (40/4 means 40 moves in 4 minutes)

May 31, 2014

After the last CCRL update (many thanks to all testers !), these are the ratings of Orion v0.1 :

TC (*)RankEloGames
(*) Time control (40/4 means 40 moves in 4 minutes)

May 24, 2014

Orion v0.1 is now listed in CCRL (in the "complete list" only, because It played less than 200 games) !

After 30 games played, Orion has been evaluated at 2194 elo. The error margin is quite big (+/- 116), but totally normal since only a few games were played. I think its real level is closer to 2078 :-)

May 21, 2014

I'm very happy and proud to release the first version of my UCI chess engine : Orion v0.1 !

I started to work on it several years ago, as a hobby, but decided to rewrite it entirely (and more seriously) at the beginning of the year, switching from Java (easy for prototyping) to C (easiest to distribute).

It includes :
  • Alpha-beta with Principal Variation Search
  • Transposition table (configurable size via UCI option)
  • Iterative deepening, Quiescence search (captures and promotions)
  • Futility pruning, Adaptive null move pruning, Aspiration windows, Late move reduction
  • Very crude and basic endgame knowledge (3 and 4 pieces)
  • Basic evaluation function (mobility, passed/isolated pawns, etc.)
  • Plain magic bitboards used for rooks/bishops attacks
My long term goal is to reach 2500 elo (one day ?!), but for the moment, this version seems to have, let's say, some room for improvement :-)

It's an 100% original work (no fork/derivative), a lot inspired by chessprogramming.wikispaces.com, and ideas taken from the excellent blogs of Jonatan Pettersson (Mediocre) and Thomas Petzke (iCE).

In order to use Orion, you will need a GUI like Arena.

Last but not least, many thanks to Graham for accepting Orion to enter the CCRL competition !

Please enjoy !


Orion is free : you can download and use/test it without limitation. The zip contains a Windows executable and a personal logo (astronomy is another passion). You are allowed to redistribute it, on the absolute condition that you don't modify the executable and the logo. Sources are not included since development is in a too early stage.