NEWS of GNU Chess
Copyright (C) 2001-2020 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
Version 6.2.7 (May 2020)
- Minor fixes in the build system.
Version 6.2.6 (April 2020)
- Fix buffer overflow on load EPD file.
- Fix move validation when cleaning up moves, e.g. accepting '0-0'
for O-O'.
- More consistent use of period in translatable texts.
- Minor fixes on compilation warnings.
- New and updated translations.
Version 6.2.5 (July 2017)
- Command history based on readline.
- New commands: coords/nocoords to enable/disable coordinates
when printing the board.
- Command pgnsave will prompt the user to overwrite or not an existing
file instead of appending the current game to the file.
- New languages.
- Bug fixes.
Version 6.2.4 (October 2016)
- Print error for invalid move.
- Truncate user input if longer than 128 characters.
Version 6.2.3 (September 2016)
- Quit after compiling book with option -a (--addbook).
- Updated translations.
Version 6.2.2 (October 2015)
- More robust program exit concerning threads.
- Detailed error messages for bad FEN syntax.
Version 6.2.1 (January 2015)
- Man page in English.
Version 6.2.0 (January 2015)
- "Tighter connection" with XBoard by means of an engine file and a
logo, as expected by XBoard (>= 4.6.0).
- Some cleanup (typos in info and removed trailing spaces in sources).
- Uppercase chars only for piece names, as Fruit doesn't like lowercase.
- A man page based on help2man.
Version 6.1.2 (July 2014)
- CFLAGS replaced by CPPFLAGS in info.
- Fix for correct handling of castling moves.
- Include translations to other languages.
Version 6.1.1 (November 2013)
- Include translations to other languages.
- Minor corrections in translatable strings.
- Migrate frontend to C++.
- Use autoconf 2.69 and require it in configure.ac.
- Use automake 1.14.
Version 6.1.0 (November 2013)
- Add support for package internationalization based on GNU gettext.
- Include first translations provided by the Translation Team.
- Graphic mode, a new board shape based on the unicode characters
for chess.
- pgnreplay command, similar to pgnload, with the capability of
manually showing a saved game step by step and moving backwards.
- Fix bug in setboard.
- Avoid using 100% CPU in UCI mode.
- Rename the small book.bin as smallbook.bin.
Version 6.0.93 (October 2013, pretest version of v6.1.0)
- Fix gettext support.
Version 6.0.92 (August 2013, pretest version of v6.1.0)
- Fix gettext support.
Version 6.0.91 (August 2013, pretest version of v6.1.0)
- Fix gettext support.
Version 6.0.90 (August 2013, pretest version of v6.1.0)
- Add support for package internationalization based on GNU gettext.
- Graphic mode, a new board shape based on the unicode characters
for chess.
- pgnreplay command, similar to pgnload, with the capability of
manually showing a saved game step by step and moving backwards.
- Fix bug in setboard.
- Avoid using 100% CPU in UCI mode.
- Rename the small book.bin as smallbook.bin.
Version 6.0.3 (March 2013)
- Run autoreconf and configure based on autoconf 2.69 and automake 1.13
to get rid of these vulnerabilies:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2009-4029
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2012-3386
- Update configure.ac to automake 1.13.
- If in manual mode, keep it after undo.
- Remove some unused code.
- Avoid crashing when importing book_1.01.pgn
Version 6.0.2 (March 2012)
- New option --addbook to compile a book.
- Maximum file name length of EPD files extended to 127 characters.
- Book file allowed to be read only unless the BookLearn option is set.
Version 6.0.1 (August 2011)
- Allow kibitz for solve command.
- If gnuchess.ini is not found, report error before prompt.
- Fix 'book on' command.
- Fix 'book add' command.
- Insert sleep(0) in adapter thread - prevents from crash for
solveepd with st 30.
- Typo in info file: 'book.dat' replaced by 'book.bin'.
- Correct INSTALL: 'cd src' before './gnuchess'
- Remove some unused code.
Version 6.0.0 (27 April 2011)
- First official release of GNU Chess version 6!
- iq6.epd no longer included in the distribution - stored in Subversion.
Version 5.9.92 (24 April 2011)
- Implement 'book *' commands as in v5.
(Implemented by extending the protocol messages between frontend and
adapter. Engine book options uncontrollable, since I am more reluctant
to modify the protocol between adapter and engine (UCI), but it could
be done.)
- Implement v5 command 'hash on/off'.
(UseTrans to be variable and driven by new option.)
- Implement v5 command 'null on/off'.
(UCI option NullMove Pruning)
- Implement v5 command memory.
(UCI option UseTrans)
- Implement v5 command memory N.
(UCI option Hash)
- Remove v5 commands hashsize/hashsize N. Memory command replaces them.
- Hard mode at startup.
- Implement v5 command-line options not working in the previous version:
--post
--easy
--manual
--memory
- All pieces of text doc transformed into texinfo.
- Include v5 script gnuchessx for xboard mode.
- Implement script gnuchessu for UCI mode, similar to gnuchessx.
- Set writing to adapter.log to false by default.
- Default config so that the config file gnuchess.ini is not mandatory.
Version 5.9.91 (14 January 2011)
- Relax dependency on config file gnuchess.ini
New in gnuchess 5.9.90 (10 January 2011, first pretest version of v6.0.0)
- Fruit 2.1 engine, by Fabien Letouzy
- Polyglot 1.4 adapter, by Fabien Letouzy
- Three decoupled components: frontend, engine and adapter
- UCI mode, providing UCI interface, through -u/--uci command-line option.
New in gnuchess 5.07:
- New PGN parser handles annotated PGN when creating opening book
- Additional command line options
- gnuchessx script added
New in gnuchess 5.06:
- Added code for pondering and analysis mode
- Added white/black commands for use with icsDrone
- Command line options now follow GNU standards (./gnuchess --help)
- Some optimisations added
- Book may be stored in /usr/share/games/gnuchess/book.dat
- Program no longer starts search from scratch every move
New in gnuchess 5.05:
- Fixed a potential buffer overflow in pgn.c.
- General code cleanups, bug fixes, and probably introduction
of new bugs, especially in pondering related code
- The opening book is now looked for in
/usr/lib/games/gnuchess/book.dat if it is not found in the
working directory.
- Changes for easing compilation with MSVC
- Removed support for the Novag Universal Board. The recommended
alternative is to use the winboard driver for this board, which
is linked to on http://www.tim-mann.org/extensions.html
New in gnuchess 5.04:
- Bug fixes (as always)
New in gnuchess 5.03:
- Bug fixes (The infamous "illegal move" bug should be dead by now.)
- Architecture independent binary book. Yes, you may now move your
binary book around between little and big endian, 32 and 64 bit
machines and it should not break.
- Build system is now automake/autoconf, should ease porting gnuchess
to your favorite strange architecture. (Hell, what about gnuchess on
cellphones...?)
Version 5.03
Book handling rewritten, and other major changes collected and applied
by Stuart Cracraft before use of CVS. Book need to be remade from PGN.
List of Grandmasters we "trust" in generating the opening book was
extended.
Contributed Bug fixes - various.
Code placed under CVS after some minor changes to 5.02.
Opening book not placed under CVS - too large.
Other changes managed under CVS
Installation instructions corrected "book create" to "book add".
Makefile modified to work with OpenBSD make.
Use of C++ reserved words as variable names removed for ease of reuse.
The C Macro i386 replaced with Endianness test for portability.
Lots of unreachable code removed to make it more readable.
"#ifdef debug" and "#ifdef never" code removed.
Removed problem with "space" on the end of filenames.
Handle XBoard SIGINT gracefully (Caused Solaris Xboard problem).
Reduced default hashtable size.
Deleted Crafty style bad trade code as it was incorrect.
The calculations for hung and pinned pieces were using stale
information in the calculations. All relevant code was removed
from the position evaluation routine.
Fixed loop bound error that allowed King to remain in check!!!
Made input buffers consistent to stop crash on long commands.
Correct hashtable handling of En Passant.
Fixed EPD output when loading a game from file with Black to move.
Fixed file handling problem extending opening book.
Various modifications to SortMove to encourage examination of
pushing passed pawns, centralisation, before other moves. Some
modification have little effect, as the calling of sorting routines
is quite complex.
Added various EPD files for developer testing. These files cannot be
included in the released tar file until copyright issues are resolved.
Removed Outside passed pawn bonus from Evaluate as it was
incorrectly in the pawn hash section.
Removed the chess_faq.html file from the distribution, as this
belongs on the GNU web site.
Version 5.02
Various bug fixes.
Version 5.01
Sun Mar 4 11:02:52 EST 2001 - book/book.*
Stuart Cracraft <cracraftt@gnu.org>
Expanded opening book
Sun Dec 12 11:42:10 EST 1999 - src/version.c
Patrick Gundlach <gundlach@irb.cs.uni-dortmund.de>
fflush stdout in Xboard startup (i.e. "Chess" herald)
Version 5.00 *** RELEASE *** (September 30, 1999 - cracraft)
o Found that after first ^C interrupt to running program a second one would
exit it. Added a new signal (..) call in EndSearch. Okay now.
o Structure the tree (doc, book, src, etc.)
o Rename the tree from gnuchess5.0 to chess-5.00
o Revise version.h.
o Revised copywrite.
o Revised COPYING (update FSF address).
o Default to post mode (statistics) if not xboard.
Version 5.00j
- integrated 1.21k from Kong.
- added
traditional anti-computer locked pawn structure penalty
traditional anti-computer stonewall pawn structure penalty
crafty's eight pawns penalty
old cobalt's ahopen traditional anti-computer edge-of-board attack
center pawns
shortened time until queen penalty (4 moves instead of 8)
EICS 5/31/99
Games: 83
Ave.opp: 1882
Percent: 77
Result: 63W + 4D + 16L = 77 %
Rating: 2093
FICS 6/15/99
Games: 125
Ave.opp: 1766
Percent: 81
Result: 100W + 10D + 15L = 81 %
Rating: 2017
Version 5.00i
- use GNU 4.0 eval instead. toss out evaluation.
- Win-at-Chess test: 229/300 at 5 seconds per move. 10,949,825 nodes
1507 seconds
- Add Queen+Piece threat extension from Kong.
- WAC: 235/300 at 5 seconds per move. 9,656,161 nodes. 1525 seconds.
- Add the whole GNU 4.0 style calling sequence in Evaluate (lazy,
single lone king, etc.)
- WAC: 213/300 at 5 seconds per move, 17,911,670 nodes. 1437 seconds.
- FICS result:
Games: 34
Ave.opp: 1836
Percent: 85
Result: 28W + 4D + 2L = 85 %
Rating: 2132
Version 5.00h
- book.c: when in XBOARD mode, the book needs to be quiet without status.
- eval.c: some formatting
- Win-at-Chess test: 219/300 at 5 seconds per move. 11,864,883 nodes.
1441.7 seconds (out of 1500 permitted).
- eval.c: penalize knight on rim even more.
up undevelopment penalty.
Version 5.00g
- Add Crafty-style bad-trade code for bad piece exchange penalty.
Version 5.00f
- Kong contributed rotated bitboards move generator.
It tests 21% faster than the old move generator,
yet overall program speed is about 8% slower based
on testing.
- Added ROOKTRAPPED code for rook trapped by king.
Version 5.00f
- BUGFIX: Kong provided a fix to prevent segmentation faults in
certain rare positions:
6Q1/8/8/4K3/8/8/p7/1k1 w - - bm 1; id 1;
- based on analysis of 7 lost games last night it was
noted that 6 of these were in positions where the program
played other than double king-pawn or double queen-pawn
instead opting for non-classical openings, so...
fix to always play double-pawn as long as the evaluation resolves
to that order of moves once book has been scored.
this is done by having the program choose from between the
top 2 moves for white's first move (excluding Nf3, but including
e4 and d4) and only the top 1 move for black's first move
(excluding non-kp/qp replies to KP/QP by white). For odd
openings like Reti or Nc3, fairly good moves are picked with
the above algorithm, that may be preferable to just having
only kp/kp or qp/qp for this algorithm).
- BUGFIX: fix problem that resulted in friendly king not being
penalized enough for being far from enemy passed pawns.
- FEATURE: Add DistMap[m][n] array. This array has all
bits turned on that are n squares away from the m square where
m is A1..H8. Aids in rapid diagnosis of distances.
- FEATURE: Add penalty for every enemy pawn within 3 squares
of the friendly king in the opening and middlegame: KINGNEARENEMYPAWN.
- FEATURE: Add penalty for no friendly minors or queen within
3 squares of king in opening or middlegame: KINGNOSUPPORT.
Games: 27
Ave.opp: 1631
Percent: 96
Result: 26W + 0D + 1L = 96 %
Rating: 2132
Version 5.00e (beginning of March)
- try increasing pawncover values -- no good.
- try diminishing underattack values -- seems good.
- add pawn majority/minority calculation
- add in better connected passed pawn evaluator
- double penalty for open files adjacent to or on king's file if
enemy queen present.
Games: 91
Ave.opp: 1763
Percent: 87
Result: 79W + 2D + 10L = 87 %
Rating: 2085
Version 5.00d (late February)
- cleaned up version prior to all the mods to get rating back.
- one night result:
Games: 29
Ave.opp: 1616
Percent: 89
Result: 25W + 2D + 2L = 89 %
Rating: 1967
- fix up PGN save-to-file routine. Was putting black in result.
- ScoreDev returns only if fully developed.
- Diminish connected passed pawn penalty.
Games: 104
Ave.opp: 1797
Percent: 77
Result: 80W + 2D + 22L = 77 %
Rating: 2008
Version 5.00b (late January)
search.c - Razoring. This applies at depth == 3. If we are more
than a Q behind and there is no extension, then reduce
the depth by 1. Extended futility pruning. At depth == 2,
if we are more than 600 points behind and there is no
extension, then we only look at checking moves & captures
which bring the material score back to alpha. Everything
else is pruned away. This is an extension of the basic
futility pruning which applies at depth == 1.
cmd.c - modify so that all games go to game.nnn and the
log of their searches go to log.nnn where the two
nnn's match.
version.c - split off VERSION/etc info into version.h
Makefile - make version.c depend on version.h
pgn.c - have PGNSaveGame record player's names based on "name" command
common.h - adjust knight and bishop values
iterate.c - was not taking up to 2 x nominal time per move when in
bad situations. fixed.
book.c - for random choice amongst top N moves of preferred book
now sorts all moves by stored book score and picks
randomly amongst N based. Previous algorithm was flawed.
eval.c - add penalties for attacks against ones king in
- add OPENGAME heuristic (1/4 pawn reward for positions
in which root position either side has more than 6 pawns
and in the leaf position both sides have <= 6
(idea due to Larry Kaufman and Don Dailey of Socrates)
- lots of work on development scoring.
- Win-at-Chess test: 233/300 at 5 seconds per move. 14,940,780 nodes.
- Rating went to FICS 2050 with all the positional changes on 1/31/99.
- make king attacks per piece to reward multiple attacks to
same square by multiple pieces
- anti-stonewall
- credit protectors in front of king and penalize attackers.
- penalize repeat pawn moves before development complete.
- rating maintained at FICS 2049.
Version 5.00a (13 Dec 98)
- integrated with WinBoard 4.0 / Xboard
- post/nopost (show iterative deepening)
- time controls (level, fischer, sudden-death, time, otim, etc.)
- works properly with FICS (Free Internet Chess Server)
- added opening book capability.
- futility pruning according to Kong.
- weak back rank handling for kings
- canned attacks against computer's king (via opening A/H file)
- penalize early minor piece repeat moves.
- wingpawn advance before castling penalty.
- Win-at-Chess test: 233/300 at 5 seconds per move. 14,977,757 nodes.
- Convert it to properly run on a standard Unix system, not just PC's.
- Make it work with "configure".
- Distribute to beta-testers
- eval.c - PawnSq[], make penalty for d2/e2/d7/e7 pawns
KingSq, KnightSq, PawnSq improved
eval.h - PINNED* worsened
- BISHOP_PAIR from 40 to 25. beta tester input.
- iterate.c - disable Hyatt more-time-after-book algorithm
disable Chua's dont-start-every-new-iteration
- this version made a 115 point rating jump (to FICS 2030).
****************** BEGIN GNU 5 (Stuart Cracraft) ********************
Version 1.19 (18 Jul 98)
a. Found problems when PV not updated when best >= beta; changed this
in both Quiesce() and Search().
b. A ValidateBoard() function.
c. Bug fix in SwapOff(). In Evaluate(), position with KNN with no
pawns wasn't being scored as 0; done.
d. More accurate & faster hung piece evaluation.
e. We skip null search when MATERIAL+ValueP <= beta instead of alpha.
This makes more sense as we are only interested in beta. Also if
the hash table returns an upper bound, the score < beta, so forget
about doing the null test. This both gives about 6% reduction in
nodes searched.
f. In Search(), when doing TTGet, g0 is destroyed even though we use it
in the null test later. This is fixed. Passed pawns made less
valuable; increased CONNECTEDPP from 450 to 650 to compensate.
g. One-reply extensions should be checked before probing the hash table
otherwise, such a probe will take place at a lesser depth than it
should. The algorithm to prune if no faster mate is found is
also brought forward to before the hash probe.
h. When all root-moves fail low, it is still a good idea to try the
best move found at the last iteration first.
i. Sometimes pawn-to-7th rank extensions wasn't being carried out.
This is fixed; also these extensions are only done at the leaf only.
If a root move is a recapture, it is extended as well.
j. Bonus/penalties for rook behind/in front of passed pawn. For ending
don't give bonus for rook on open files as rook behind passed pawns
are stronger.
k. SwapOff() wasn't handling promotion moves at all; this is now fixed.
Some of the sort algorithm has to be changed to take into account
the update to SwapOff. Also minor bug fix to AddXrayPiece().
l. Penalize side where a pawn base is under attack by opponent's pawn.
m. At SearchRoot() we don't need to do any extensions. For recapture
extensions, we only extend if it is capture of equal or more
material so as to follow sacrifices (e.g QxP+ KxQ etc).
n. Bonus for pawn on c6/f6 if opponent king is in the appropriate
corner.
o. Extension for useless interposing moves. Limit recapture extensions
to below Idepth+2.
p. For PV's we no longer back it up from the root. Now the whole
PV is taken from the hash table except for the first move. This
is a much cleaner way of managing it, saving code in search.
Otherwise, the PV that is return isn't always correct and its
really very difficult to fix.
q. There were some bugs with HashKey calculation in move.c, init.c
and hash.c. These have been fixed. The idea is that for ALL
positions in a game, the HashKey must be equal to the HashKey
calculated if the positions are epd-loaded. Got rid of CptrCnt[]
array; I no longer use it for capture extensions.
r. King position is now stored in the variable board; we no longer
need to run leadz (board.b[side][king]) anymore, which takes place
in quite a number of places!
s. An AttackXTo() routine which generates a bitboard of all pieces
of side which attack a square. This includes x-rays. Bug in
GenCheckEscapes() whereby a pawn capturing a checking piece is
not checked for promotion. When Idepth <= 3, we don't do null
move. This allows us to catch some mates in 2 which would
otherwise be pruned away by the null move.
t. Added in threat extension code. A mate at any depth is better
than a non-mate score, so it will replace it in the ttable.
More "bug fixes", eg. sometimes null moves terminate the PV,
hopefully this is all fixed in this release.
u. A TTGetPV to pull the PV from the hash table. This works better
than TTGet which can sometimes miss the PV due to the way the
hash tables are managed.
v. Bonus for fianchetto bishops. Minor change to TTPut() whereby
occasionally the same position can occupy both slots but the 2nd
slot has a lower draft. The 2nd slot is wasted. This is changed
so that this waste will no longer occur.
Version 1.18 (18 Mar 98)
a. In MakeMove(), when a rook is captured, the castling flag has to be
updated too. This also means that in genmove.c, when generating
castling moves, it is not necessary to check if the rook is on its
original square. However this check hasn't been removed yet.
b. Add "epdsave/save" command.
c. Debug code in quiesce.c wasn't being activated; fixed.
d. In ttable.c, use & for calculating hashindex rather than the more
expensive modulo operation. Gain a couple of percent speedup.
Also fix the hashsize command so that it is also a power of 2.
Also get rid of modulo operation everywhere else in the code.
e. For connected pawns on 6th/7th rank only apply super bonus when
the enemy only has rooks.
When researching a fail high move & it fail low, immediately set
alpha to -INF and research it. This assumes that the original move
did not fail high.
f. PhasePick() was sometimes trying out the Hashmv twice resulting in
wasted time. Fixed by making Hashmv[] an array.
g. Bug in trade down code fixed. Also modified the way worstscore
was calculated resulting in a significant speedup in Evaluate().
Fine tune ScoreB().
h. Added a FindPins() function which returns a bitboard of all pinned
pieces. This is used in eval.c for evaluating pinned pieces.
i. Modify way in which sorting of captures was done. This led to a
reduction in the quiescent search speeding things up slightly.
j. For killers, only update them if best >= beta; this gives much
improved pruning. Remove killer updates in SearchRoot().
Remove transposition lookup & updates in SearchRoot(). Got rid of
pbest in SearchRoot().
k. In quiesce(), only update the PV if the score > alpha, not when
score > best. When a mate in N plies have been found, at the N-1
ply, we don't search the opponent moves; we only check to see if
he is mated. Simplify SearchRoot().
l. If the hash table returns an upperbound, then we don't want the
move that is returned, so set Hashmv=0. This improves pruning.
m. SquarePawnMask[] for pawns on 2nd rank is wrong; it is now set to
mask for pawns on 3rd rank as they can advance 2 square. SwapOff()
used to assume that the side to move is the one moving the piece.
This has been changed to that SwapOff() can be used for any side.
Bug fixed in evaluation of trapped bishop. Bug in GenCheckEscapes()
whereby an e.p. capture was allowed even if the pawn is pinned;
this is fixed. A nicer and bigger board.
n. For endings with opposite colour bishops, half the score as they
are mostly drawish. Instead of penalizing weak pawns, give bonus
to pieces which attack weak enemy pawns. Lots of evaluation tuning.
Commented out ShowThinking() resulting in faster search. All this
has improved the nodes per second by 50%! Fix bug in MakeMove()
whereby if a R captures another R, the castling flag for the
captured rook is not cleared.
o. Updated FindPins() to include more pin situations. Introduce a
variable called computer; this hold the colour that the program
plays. Make a trapped bishop part of lazy evaluation as it gives a
high penalty. Promotion weren't taken into account in SortRoot().
p. A basic KPK evaluation for certain positions. Another bug in
GenCheckEscape(); a promotion move to escape check isn't taken into
account. Introduced a board.pmaterial[] variable which holds the
pieces total value for a side. PHASE is now calculated using only
pieces values. In Quiesce(), when side is in check we don't prune
even if best >= beta; this is now fixed; when in check, we see if
we are checkmated, if not and there is a beta cut, do it saving
some branches. History was updated everytime best > alpha; now it is updated only when best >= beta, or when a score > alpha has been
found. All this gives rise to improved pruning about 2-3 %.
q. Some fine tuning of passed pawn eval. Add quiesce move to ttable
so that it can appear in the PV.
Version 1.17 (9 Feb 98)
a. Added very elementary hanging piece evaluation.
b. For square of the pawn, instead of adding ValueQ - ValueP, we
a fraction of ValueQ based on how far advance the pawn is. This
is to encourage the pawn to advance and queen. Fix a bug in
IsLegalMove() whereby an en-passant was considered illegal.
c. More accurate hanging piece evaluation.
d. IsLegalMove() was missing out enpassant captures. Fixed.
e. Added a ptype[] variable to distinguish between pawn & bpawn;
f. In Search(), initialize PVlen before checking for draws. This fix
problems with illegal moves in the PV (e.g. GMG1.epd 42).
g. Renamed Pinned() to PinnedOnKing(). A new Pinned() function will
be written to be more generic. Minor change to SearchRoot(), the
first move is also moved within the main loop, making things tidy.
h. Xboard support.
i. In Search(), the first move is also moved into the main loop. This
is to make the code better suited for adding threat extensions.
Game50 variable wasn't being properly updated; fixed.
j. Trapped bishop at A7/H7/A2/H2. Rook moved before castling is now
penalized. Minor optimization in eval.c. More eval tuning.
k. Also promotion moves were not being sorted properly; this is fixed.
l. board.ep was initialized to 0; now its -1 fixing a bug when
promotion happens at A1 square (square 0).
m. Instead of storing the whole board HashKey into the ttable, we now
store the top 32 bits, saving memory. Same for Pawn table.
n. Fix bug in backward pawn detection. Fix bug in search whereby
sometimes the best move wasn't being properly set. Fortunately,
this happens quite deep in the tree, so not much improvement might
be seen. Change the way that scores are returned from the hash
table probe to improve pruning.
o. Trade down bonus implemented. Recaptures extensions modified so
that only recaptures of same value & square are extended.
p. In Quiesce(), check for mates as well.
q. Killers at ply-2 is also used for sorting. Reduced tree size
slightly (2-3%).
r. Moves in the Quiesce() search were not being recorded in the PV.
This is now fixed.
s. Bug fix in evaluation of square of the pawn whereby if the opponent
is on the move, the pawn isn't scored properly.
t. Phase pick is implemented. Code seems to be working. Also bug
fixes in IsLegalMove() and Evaluate().
Version 1.16 (26 Jan 98)
a. Added a Mvboard[] array which returns the number of times a piece
on [sq] have moved. Use it for penalizing early Q moves.
b. ScoreDev() returns only development of side-to-move instead of
white-black.
c. Separate Search() into a SearchRoot() which is called at ply==1
and Search(). Some modifications in search.
d. Added back GenAtaks() into evaluate when doing slow evaluation.
Modifications in the ScoreX() routines to make use of attack tables.
e. Fixed a bug in UnmakeNullMove whereby the board.ep variable wasn't
correctly restored.
f. Added the passed BitBoard into the pawn hash table allowing us
to save the passed pawn board into the table.
g. In evaluate, when one side has no mating material, make sure the
score is never > 0.
h. Added in Square of the pawn evaluation. Fix a bug in ScoreP whereby
passed pawns information was being changed. In EvaluateDraw(),
fix a bug whereby 2N vs 2N wasn't a draw.
i. Fix a bug which sometimes put an illegal move in the PV. This
was happening when an EXACTSCORE was returned, but the PVlen was
incorrectly set.
j. Lots of changes/tuning to eval.c.
k. Added in an IsLegalMove() function to test if a move is legal.
l. Added a Pinned() function to test if a piece is pinned against
the King.
m. Added a GenCheckEscape() routine to generate move when a king is
in check. In SearchRoot(), there is no need to check if a move
is legal as all root moves are legal.
n. If King is in check, generate check escapes only and if there is
only 1 move, extend by another move.
Version 1.15 (16 Jan 1998)
a. Convert AlgbrMove() to return char * rather than void.
b. In the quiescent search, use SwapOff() to see if a capture is
futile and prune it. Removed as it wasn't working well.
c. Big bonus for connected passed pawns on the 6/7th rank. Solves
WAC/2 easily.
d. Bug fix and clean up of code in sort.c. Results in improve capture
sorting and better pruning. Got rid of DeepExtCnt; not used.
e. For search extensions, limit capture to maximum of 2 and checks to
maximum of Idepth, the iteration depth.
f. SwapOff() wasn't working for non-captures as pointed out by Stuart.
Fixed SwapOff(); appears to be okay now. Used SwapOff() in capture
move ordering; seems to help a bit.
g. In Search(), move the Quiesce() call before the ttable probe.
Slight improvement in pruning and ttable stats are now much higher.
h. Still another bug in AddXrayPiece() was fixed.
i. Slight change in GenMoves() to speed it up slightly.
j. Implemented pawn hash table. Achieves good increase in nps (25%).
k. Added in a SquarePawnMask[] array. This is to determine if a king
is able to stop a passed in a king and pawns only endgame.
l. Material values of 100,350,350,550,1100. Also some optimizations
in move.c. PHASE modified for new material values.
m. Implemented a two-tier transposition table. Minimal gain in tree
size reduction.
n. Only store non-captures as killers; try killers after captures
in sort. This gives more than 30% reductions in nodes searched.
Also fix a bug in SortMoves().
o. Only give bonus for rook on 7th rank if enemy king is on 8th rank
or there are enemy pawns on 7th rank. Other bug fixes and tuning
in eval.
p. Recognize and penalize backward pawns.
Version 1.14 (3 Jan 98)
a. Fixed bug in solve.c whereby the test for a correct solution is not
correctly done (pointed out by Stuart).
b. When searching for mates, eval just return MATERIAL saving time.
c. Uses EPD format rather than FEN; also clean up ParseEPD; fen.c
now called epd.c
d. io.c renamed to output.c. Game phase is now 1-8 (opening-ending).
e. In quiesce(), if a capture cannot bring the score near alpha,
don't search it, speeding things up.
f. If we have a rootscore much worst that our previous iteration
rootscore, we continuing searching. (Fix from Stuart).
g. Got rid of nxtline, bstline way of updating the PV. Instead use
the method in cheops, resulting in much cleaner code.
h. Got rid of savePVar[] array and all the code related to it.
What its for, I can't remember.
i. SortMoves() takes into account moves towards the centre. Pruning
is slightly improved.
j. AttackFrom() function is added. This returns the bitboard of
squares attacked by a piece. Remove GenAtaks() and other code
in eval.c which required the use of attack tables.
k. Bug in ScoreDev() whereby an early Queen move which should be
penalized isn't. Various bug fixes & tuning in eval code.
l. PGNReadFromFile() is able to read the 1st game in a pgn file.
m. In the null move, instead of searching with window [alpha,beta],
we search with [beta-1,beta].
n. Added in a directions[][] array. This array is used in swap.c
when checking for x-ray pieces. Added AddXrayPiece() routine
which is used in the static evaluator.
o. Got rid of foundPV variable. It isn't really necessary.
p. Don't flag mate score in ttable as exact score; they aren't.
q. Change some (best >= alpha) code to (best > alpha) in Search().
What was I thinking of then!?
Note: From this point on, changes within a release are labelled as a-z. This
is also reflected in version.c
Version 1.13 (1 Jan 98)
Got rid of history.c. Killer is stored only if it is a beta cut.
Fix bug in pawn eval for isolated pawns and passed pawns. Functions
like ScoreDev & MATERIAL now return the score for side to move instead
of score for white. This also fixed a bug in the null move condition
whereby MATERIAL was only seen from white point of view when it should
be from the side-to-move view. Got rid of SlowEval variable speeding
up things quite a bit. GenAtaks() was NOT called in Evaluate(); this
is now fixed.
Version 1.12 (27 Dec 97)
When a mate in n-ply is found, the search will never go deeper than
n-2 ply. Fix some bugs in search.c. Mate scores in hashtables are
now always flag as EXACTSCORE, fixing some bugs in mates. At ply 1,
we now don't return the hash score if it is an exact score as we
need to search the rest of the moves. In ttable.c, SANMove() should
not be called as GenMoves(ply) was never called. This affected the
debug code. Now algebraic moves are printed rather than SANMove for
ttable debug code. Fix repetition code, now gmg1.ci/42 can be solved.
In iterate.c, foundPV should be set to false when a research is
being done. A Hashmv variable is used to store the move return from
probing the hash table. This is use for move sorting.
Version 1.11 (21 Nov 97)
Nulls can be toggled on/off. Worstscore[] is now initialized to
-100 instead of infinity. EvaluateDraw() is called after iterative
deepening is over to see if the game is a draw. New routine
ScoreDev() to calculate development separately; "show eval" command
will print development score. Got rid of Developed[2] global variable.
Some tweaking in search.c. The decision to print '&' or '+' for a
PV is now in ShowLine().
Version 1.10 (29 Aug 96)
KBBK with bishops of the same colour are now recognized as draws.
Matescore now starts from 32767 instead of 9999. INFINITY
extended to 32767. Added Ctrl-C trap so that the search will end
instead of aborting the program. Originally the move returned by
a hash probe is added to the history score. This is removed and
the program show much improved pruning.
Version 1.9 (17 Aug 96)
Change the way check/recapture extensions are tested; previously
check extensions only take place at <= Idepth*2. Now a total of
Idepth+1 check extensions are allowed. For recapture, a total
of 2 extensions are allowed. This makes the program search deeper.
Fix bug whereby a promotion move (e.g. d8=Q or d8Q) was considered
illegal if the opponent tried to enter it on the command line.
Fixed a bug in the PVS search.
Version 1.8 (12 Aug 96)
A lot of leaf struct variables are converted to int, making the
program slightly faster. Search extension for pushing pawns to
7th rank. The SANMove() code is now responsible for determining
if a checking move is mate and adds the '#' sign accordingly.
This is much cleaner. Added passed-pawn evaluations. Fix bug
in eval.c where EnemyKing was wrongly initialized. Added KingSq[]
array to help King stay in the corner. Added primitive development
code; if bishops and knights are on original squares, penalize.
Got rid of Material() and substitute a macro MATERIAL for speed.
Version 1.7 (5 Aug 96)
A nullhashcode was added so that a null move will change the
HashKey (a bad bug!). Repetition code is now working correctly.
The enpassant and castling hash codes are now 64 bit hash values
instead of being bits in the HashKey. A lone king evaluator is
added in. This allows the program to perform elementary mates.
Got rid of FilterIllegalMoves() in search. Now all pseudo-legal
moves are tried; they are immediately rejected if it is determined
that they are illegal. An EvaluateDraw() routine is called early
in the Search() and Quiesce(); if the position is a known draw
(e.g. not enough mating material), no searching is done. A KBNK()
mating routine is added; this seems to be working fine.
Version 1.6 (2 Aug 96)
When displaying the PV and the end is reached, see if the rest of
the line can be found from the transposition table. The random
number generator is taken from Knuth. FilterIllegalMoves is called
to cull out illegal moves. This prunes enough branches such that
it turns out to be a gain. Speeded up FilterIllegalMoves().
Converted board.ep to short rather than using a BitBoard. Also
fast evaluation is done in Evaluate() rather than quiesce. Got rid
of epsq variable in leaf structure; it wasn't needed as a board.ep
already exists. A bug was introduced when the new random number
generator was added; the top ten bits of the hashkey was being
corrupted; this is now fixed. Speeded up null.c code and MakeMove()
UnmakeMove() routines. Got rid of piececap in leaf{} structure;
It has been integrated in the the leaf.flag variable. The leaf.f
and leaf.t variable has been merged into the leaf.mv variable.
Version 1.5 (29 Jul 96)
Mate stored in the transposition table need to be offset by (+-ply).
Pruning via killer moves has been improved. A new HistoryStore()
is created for code dealing with history & killer. InChk and
GenMoves() are no longer needed in quiesce(). All that work is the
responsibility of the full-width search. Much improved pruning.
The flag structure was replaced by an unsigned long. Got rid of the
ExScore variable. Now all calls to Evaluate() will yield the exact
score.
Version 1.4 (19 Jul 96)
Check for repetition in search (code currently not working).
Added in transposition table code. Currently there is no rehashing
done. The whole PV was returned to the top of the tree.
Version 1.3 (16 Jul 96)
For null moves, if the current material+pawn value is less than
alpha, then we don't try the null move test. The reason is that
since our position is already so poor, when playing a null move,
our score is going to be less (unless the position is zugzwang).
So its not going to be a beta-cut neither is it likely to improve
alpha. This appears to reduce the nodecount. Added a flag.ended
variable to the flag structure. When this is true, the game has
ended and typing go will produce nothing.
Version 1.2 (13 Jul 96)
For sort captures, a recapture is always tried before another
capture of the same value. This gives slightly better pruning.
Material for white & black is updated incrementally in make/unmake
move. This speeded up the program significantly. Stalemates are
recognized during the search and a score of 0 is returned.
Version 1.1 (19 Feb 96)
Added in the NULL move heuristics. Currently the null move
depth reduction is 2.
Version 1.0 (17 Feb 96) (Chua Kong Sian)
This version plays a legal game of chess. It supports all the
special moves (en passant, castling and promotion/underpromotion).
It uses the standard PVS search algorithm and incorporates the
fail-soft alpha-beta enhancement which gives tighter alpha-beta
bounds. All evaluations are only done at the end-points.
Move ordering is by captures first and also history heuristics.
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