Home * Engines * Floyd

an UCI compliant open source chess engine for study purposes and prototyping of new ideas by Marcel van Kervinck, written in C, and first released in October 2015 [1] with a permissive license [2] . Floyd can be build to run under Windows, Linux and Mac OS. Floyd had its over the board tournament debut at the IGT 2016 with a 50% score.
Hurricane Floyd [3]


Board Representation

Floyd uses an 8x8 Board, agnostic to square indexing, in the sense that it can be adapted to any of the eight possible board geometries with just a local change [4] . It uses an attack table, for each side an array of 64 bytes, with following one- or two-bit attack counters per square ...
|   Pawns   |   Minors  |   Rooks   |Queen|King |
     7..6        5..4        3..2      1     0
... as used in move generation, SEE and evaluation.


The search is a classical PVS iterative deepening approach with Zobrist key transposition table, quiescence search, null move pruning and mate distance pruning. Move ordering considers SEE and a simple killer heuristic.


Floyd's evaluation employs a vector of feature and weight pairs to calculate a score as weighted sum. In conjunction with a draw model [5] using sigmoid functions, the score is mapped to winning probabilities, suited for logistic regression tuning.
def evaluate(board, wiloVector, drawVector):
        wiloScore = ...snip... // a weighted sum of board features
        drawScore = ...snip... // another weighted sum of board features
        return sigmoid(drawScore) * 0.5
             + sigmoid(wiloScore)
             - sigmoid(wiloScore) * sigmoid(drawScore)


Floyd provides a Python API for search and evaluation functions [6] , i.e. for automated tuning [7] . It generates a compact KPK tablebase to deal with perfect knowledge, also available as stand alone project [8] [9] .

See also

Forum Posts

External Links

Chess Engine



  1. ^ Floyd 0.5 released by Marcel van Kervinck, CCC, October 11, 2015
  2. ^ floyd/LICENSE at master · kervinck/floyd · GitHub
  3. ^ Hurricane Floyd near peak intensity on September 14, 1999 at 2030 UTC. This image was produced from data from NOAA-14, provided by NOAA, Wikimedia Commons, Hurricane Floyd from Wikipedia
  4. ^ floyd/geometry.h at master · kervinck/floyd · GitHub
  5. ^ floyd/drawModel.txt at master · kervinck/floyd · GitHub
  6. ^ floyd/README.md at master · kervinck/floyd · GitHub
  7. ^ floyd/tune.py at master · kervinck/floyd · GitHub
  8. ^ Yet another KPK endgame table generator: pfkpk by Marcel van Kervinck, CCC, September 05, 2015
  9. ^ kervinck/pfkpk · GitHub

What links here?

Up one Level