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Sjaak [1],
an open source engine under the GNU General Public Licence written in C by Evert Glebbeek as younger sibling of Jazz, but able to play chess variants on various board sizes compliant to the Chess Engine Communication Protocol. Sjaak was first released in January 2011, not to confused with Ronald de Man's older private engine with the same name [2] [3]. The further extended SjaakII, released in early 2015, supports even more variants and protocols , and runs best under XBoard/WinBoard, version 4.8 (or better) [4] .



Board Representation

Despite boards exceeding 64 squares, like 10x8, 12x8, and 10x10, Sjaak is a native bitboard engine, utilizing either GCC's __int128 [6] extenstion on 64-bit platforms such as x86-64 or 128 bit vectors of integers on 32-bit platforms, the latter supporting SSE2 if available. Sjaak applies Kindergarten Bitboards to determine sliding piece attacks [7].


Sjaak uses a fail-soft alpha-beta principal variation search with quiescence, null move pruning, late move reductions and check extensions inside an iterative deepening framework with transposition table [8]. Move ordering considers the killer, countermove and history heuristics. A modified version of a SEE routine from Jazz is used to evaluate captures .


Sjaak's static evaluation takes material balance, static piece-square tables derived from heuristics based on how pieces move, mobility and king safety into account, the latter only in chess variants with one king per side [9].


See also

Forum Posts

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2015 ...


External Links

Chess Engine



  1. ^ Sjaak - Dutch given name derived from Jacob, pronunciation similar to Schaak
  2. ^ ICGA: Losing Chess by Guy Haworth
  3. ^ Re: New Spartan-Chess engine: Sjaak by Vladimir Xern, CCC, January 21, 2011
  4. ^ SjaakII 1.0.0 by Evert Glebbeek, CCC, March 18, 2015
  5. ^ Shogi by Evert Glebbeek, CCC, October 20, 2014
  6. ^ __int128 - Using the GNU Compiler Collection (GCC)
  7. ^ Chess (Jazz & Sjaak) design
  8. ^ Chess (Jazz & Sjaak) search
  9. ^ Chess (Jazz & Sjaak) evaluation

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