DiscoCheck 3.5
---------------
- no futility pruning of killer moves: scores equal in self-play, but slightly better in tactics.
- futility and eval pruning now done also at PV nodes.
- bugfix: returned the previous iteration move when mate found in certain cases.
- bugfix: print_pv was calling move_to_string with illegal moves.
- run_epd: run an EPD file, produce a nice report of missed positions and total score.
- move_to_san added.
- bugfix: calc_attacks was functionally incorrect, rewritten and speeded it up a little too.
- improved evaluation of connected passed pawns.

A new interesting feature of DiscoCheck is the EPD support, as documented in the readme.txt file!

DoubleCheck 3.4
---------------
- tuned king safety weights.
- rewritten and tuned passed pawns eval. 

DoubleCheck 3.3
---------------
- eval: added candidate passed pawns.
- tt: generation SF style: todo
- pack move_t into 16 bits: in progress
- board: pack move_t to 16 bits.
- eval: knight and bishop outposts.
- eval: improved passed pawn scoring.

DoubleCheck 3.2
---------------
- eval: increase rook on (semi)open file bonus, when on the enemy's king file.
- eval: added a tempo bonus.
- search: margin for eval pruning now increases faster with depth.
- search: fixed my lame razoring code. thanks to Martin Sedlak and Marco Costalba for suggesting
this.
- qsearch: divided by 2 the futility margin.
- qsearch: SEE pruning only at non PV nodes.
- qsearch: fixed an error in evasion pruning.
- bench: increased depth of test positions. 

DoubleCheck 3.1
---------------
- futility pruning in quiescent search improved.

DoubleCheck 3.0
---------------
- eval command now returns a full breakdown of eval components.
- eval mostly rewritten.
- aspiration windows.
- code cleanup.

DoubleCheck 2.7
---------------
- added rook on open file bonus.
- removed stdin unbuffering.
- removed the global variable SubPromotion. handle this more tidily via function parameter.
- changed piece values.
- mvv/lva sort in qsearch captures.
- removed RNB promotions in qsearch.
- remove POSIX compile flag (auto detect).

DoubleCheck 2.6
---------------
- eval_loose: penalise loose pieces a little.
- introduced an array B->st->attacks[color][piece] to simplify and speedup additional eval code.
- use unsigned i/o int wherever relevant.
- faster interfacing code when Verbose = false.

DoubleCheck 2.5.4
-----------------
- bugfix: free passer bonus was attributed when pieces were in the way, i/o the opposite.
- bugfix: relative king distance was too preponderant in the passed pawn scoring.
- bugfix: KRRBKRR was incorrectly recognized as a draw.

DoubleCheck 2.5.3
-----------------
- move_ok: rewritten efficiently (first step to prepare the lazy move ordering).
- rook and bishop promotions can be disabled (in search, not perft) with SubPromotions in movegen.c
- gen_msl: precalculate SEE only for captures.

DoubleCheck 2.5.2
-----------------
- eval: removed candidate passed pawns.
- eval: reduced penalty when a passed pawn is not part of a pawn chain.

DoubleCheck 2.5.1
-----------------
- eval: added candidate passed pawns.
- bugfix: report correct version number.

DoubleCheck 2.5
---------------
- eval: introduced king attack incentive.
- bugfix: doubled node polling frequency to avoid time losses.

DoubleCheck 2.4 (CEGT 40/4: 2415 elo)
---------------
- MAX_GAME_PLY now equals 0x400, so games can safely last 0x400-0x80 half-moves before the game stack
writes out of its allocated memory and crashes everything.
- qsearch: do not write in the TT when the move loop was empty.
- eval: mobility rewritten, should make a bit more sense now.
- search: introduced double reductions for late quiet moves.
- search: do not reduce castling moves.
- search: eval pruning rather than reduce.

DoubleCheck 2.3.1 (CCRL 40/40: 2313 elo)
-----------------
- feature: do not clear hash when ucinewgame command is received.
- feature: do not reduce passed pawn pushes into the enemy's half board.
- code: makefile added.
- code: reorganized the hash_t structure, and packed it more efficiently into 16 bytes i/o 24. The
keys stored in the hash table are now 62 bits, i/o 56.
- code: TT allocation code improved, only alloc TT at the last moment, to reduce memory footprint.
- bugfix: crashed with Hash=4096. Hash changed to min=1 max=8192 default=32.
- bugfix: PV line is now displayed in long algebraic notation, in accordance with the UCI standard.
- bugfix: 3-move repetition was causing and endless PV.
- bugfix: UCI parsing code more stable, and more verbose error messages.

DoubleCheck 2.3
---------------
* razoring and eval pruning. Unlike other engines, I reduce the depth instead of pruning, and when
the reduced depth is <= 0 then I prune.
* fixed search extension and reductions a bit.
* few minor code changes

DoubleCheck 2.2
---------------
* LMR: rationalised the reduction code. Search reductions should be safer, and more sound. Also code is
easier to read and maintain.
* magic bitboards: The generation of magic bitboards is now based on the code Umko by Borko Boskovic.
Reasons for choice:
	- Umko's implementation of magics uses 3 times less memory, so it's more cache friendly
	- Umko's code is copyleft (GPL), whilst Pradu Kannan's copyright terms are incompatible with the
	letter and the spirit of GPL free software.
* added a benchmark() function.
* qsearch SEE pruning:
	- don't prune discovered checks with negative SEE
	- prune the tt_move, like any other
	- removed the PV condition
* most sort: removed the mate killer heuristic (it was useless).
* move sort: forbid captures or promotions to "pollute" history table or killer moves.
* eval: forbid the use of calc_eval() when in check (use -INF instead, handled in the search).
* bugfix: displaying 64bit node counts now works (using the portability macro PRiu64)

DoubleCheck 2.1
---------------
* parametric PSQ. Based on Fruit, although the code is a complete rewrite, and several things have
been simplified. I'm trying to minimize the number of parameters here, with a view to do a CLOP
optimisation later. Number fo param in PSQ: 18+2*8+2*4=42, compared to 2*6*64=768 previously!
* Polling code fixed: stop command should now work on POSIX and Windows.
* drawish material recognizer: should look less stupid in dead drawn endgames!
* bug fixes: an important one being the eval "phase" casted to int (so was only 0 or 1)

DoubleCheck 2.0
---------------
* fake UCI command eval added.
* eval function significantly improved.
* UCI command depth now supported.
* UCI command nodes now supported.
* UCI command infinite now supported.
* UCI command stop supported on POSIX: untested so far.

DoubleCheck 1.4 (CCRL 40/4: 2258 elo)
---------------
* Rook eval: open/semi/closed file + 7th rank
* magic bitboards, adapted the implementation from Pradu Kannan.
* bugfix: stronger hashing to avoid TT collisions
	- rand64() now uses the much superior JLKISS64 RNG, by Pr. David Jones, UCL Bioinformatics Lab
	- 56 bit zobrist are stored in the TTable, instead of 32
* bugfix: info pv line now contains the depth, as defined by the UCI protocol.

DoubleCheck 1.3.1 (CCRL 40/40: 2183 elo)
-----------------
* bugfix: PV was not shown in GUIs. I was sending the pv on a separate line, which isn't UCI
compliant. Thanks to Matthias Gemuh for pointing this out.

DoubleCheck 1.3
---------------
* DoubleCheck is able to display a correct PV. The code was much simplified, as I simply
retrieve it from the TTable.
* bugfix: 3-move repetition. Thanks to Martin Sedlak for helping me fix this.
* other minor search bug fixes.

DoubleCheck 1.2
---------------
* Delta pruning, Futility pruning, and Late Move Reductions (can be disabled via UCI option).
* UCI option Draw was removed. A bug with repetition draws was also fixed.
* UCI command movetime now supported. Thanks to Aart Bik for suggesting it.
* various bug fixes.

DoubleCheck 1.1
---------------
* UCI option Draw. This is the score of a draw, from the point of view of DoubleCheck. Default value
is -20, meaning that DoubleCheck will (slightly) try to avoid draws, and assume that the opponent
seeks draws.
* UCI option NullMove: recursive null move pruning.
* Internal Iterative Deepening, with a UCI option to enable/disable it. It doesn't make a significant
difference in blitz; the benefit kicks-in at longer time controls (improves move ordering).
* UCI option "Hash" to set the size of the hash table in MB. Now defaults to 64 MB instead of 16.
* 7-th rank extension: when the move is a pawn to the 7-th rank, with a >= 0 SEE, then I extend by 1
ply. There was no evidence of either improvement or regression after testing this. But, intuitively,
it makes sense. And it seemed to play better in the endgame, so I kept it.
* fixed a bug in the hash table: I was potentially using results from the search in the quiescent
search, which is never a good idea.
* modified the material values, and added a bishop pair bonus.

DoubleCheck 1.0 (CCRL 40/40: 1947 elo)
---------------
* first release.

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