Fizbo is an original chess engine written by Youri Matiounine.
Current version is 1.9 and can be downloaded from the link
at the bottom of this page.
1. file "fizbo19x64" is the primary engine, and will only run under Windows and requires CPU with "popcount" instruction.
Changes in version 1.9, released December 31, 2016
Changes in version 1.8, released August 26, 2016
Changes in version 1.7, released March 23, 2016 (executables last changed April 4th 2016, to exclude illegal moves from PV, to add longer PV, seldepth/nps/currmove/hashfull/tbhits to the output, and to correct pondering bug):
Changes in version 1.6, released January 29, 2016 (executables last changed on January 31st to verify that SYZYGY files exist before using them):
1. fixed a timing bug - now engine should no longer time out.
2. fixed a bug in EGTB logic - now engine should work when only 4-piece (and not 5-piece) syzygy tables are present.
3. fixed a bug in main transposition table - now it can be made larger than 2Gb.
4. added option "UseEGTBInsideSearch": when set to false, engine will only use EGTB in root position, not inside search. This allows EGTBs to be used when they are stored on hard drive and not on SSD.
5. various small modifications to search and evaluation, resulting in approximately +30 ELO for 1 core play.6. multiple changes to parallel search, which now should work as intended. Estimated benefit from running on 4 cores is around +90 ELO.
Changes in version 1.5, released August 16, 2015 (executables last changed on August 29th to remove default SYZYGY path, and to correct a bug in parallel search; single CPU search is unchanged.):
1. engine is now using UCI protocol. This should make it more compatible with modern chess interfaces.
2. various small modifications, mostly to search, resulting in approximately +40 ELO.3. parallel search had a bug fixed, and should now work as intended. Estimated benefit from running on 4 cores is around 80 ELO.
Changes in version 1.4, released May 18, 2015:
1. various small modifications to search and evaluation, resulting in approximately +30 ELO.
2. engine can now change size of main transposition table on the fly, using Xboard protocol command "memory N". Size of TT is rounded to nearest power of 2.
3. engine can now use 3-4-5 piece syzygy endgame bit-bases and table-bases. Path of syzygy tables can be passed to the engine using Xboard protocol command "egbpath TYPE PATH". On engine start-up it is also taken from environmental variables DTZDIR and WDLDIR, for DTZ and WDL tables respectively.4. parallel search is now more advanced, allowing multiple active split-points at the same time. This should improve performance on 8 and more CPU cores (sadly, performance on 4 cores is mostly unchanged, aside from increased strength of single core engine).
Changes in version 1.31, released November 21, 2014:
corrected a bug that occasionally crashed the engine (sometimes castling move was made in a position where after castling king would be under attack by opponent's king). Also made some minor changes to evaluation, so that results of version 1.31 will not match results of version 1.3! But playing strength is mostly unchanged.
Changes in version 1.3, released November 12, 2014:
1. improved transposition table managementfixed a bug
reduce size of TT entry to 8 bytes
started using TT in Q search
2. added aspiration window
3. various small modifications to search and evaluation.
Single CPU improvement over version 1.2 is around +80 ELO (based on self-play at 1 sec/move).
Changes in version 1.2, released July 27, 2014:
1. improved search
more aggressive LMR
better time management
other misc search enhancements
single CPU improvement over version 1.1 is +70 ELO (based on self-play at 1 sec/move)
2. added parallel search
based on a version of enhanced PV splitting algorithm - only one split-point is active at a time
activated by Xboard command "cores N"
supports up to 8 cores, but scaling beyond 4 cores is very poor
estimated improvement on 4 CPU cores is +90 ELO (based on self-play at 1 sec/move)
Features of version 1.1:
released May 10, 2014uses Winboard protocol
no opening book
is compiled without "AVX" switch, so should run on any Intel "i" CPU
two versions. The one ending in "no_pc" does not require "popcount" CPU instruction