//
// Determine whether a Draw should be sought or avoided, by adding
// the estimated handicap to an equal evaluation of Zero depending
// on the game phase, and the relative strength of the two players.
//
protected Eval contempt()
{
GameState.AtomicIncrement(ref State.DrawTotal);
var mDrawValue = (Eval)(-State.Contempt); // Strength advantage of White over Black
return(mDrawValue);
}
// ~2.3 MHz: slowed mostly by IsLegal() and only slightly by resetMove()
protected Boolean tryMove(ref Move move, Boolean bFindRepetition = true, Boolean bQxnt = false)
{
CurrentMove = move; // Current Pseudo Move
(bool bPrevented, bool bRestricted) = isPinned(move);
if (bPrevented) // Skip moves which violate known pins
{
GameState.AtomicIncrement(ref State.PinSkipTotal);
return(false);
}
//[Timer]timeMove(move);
//
//[Note]resetMove() is called here because it is needed for every subsequent move. This leaves
// a window between the time initNode() initializes a node and when resetMove() is first called.
//
resetMove();
this.move(ref move);
if (IsDraw0())
{
clrEval(); // Captures and Pawn moves invalidate staticEval()
}
//[Note]If En Passant was possible, any move ends a Transposition Group
if (Parent.IsPassed())
{
setDraw0();
}
testHash(); // Conditional
var bLegal = IsLegal(bFindRepetition, bRestricted);
if (isDefined(move))
{
if (bLegal)
{
CurrentMove = move = annotateEarly(move);
}
else
{
restrictPiece(move);
}
}
State.IncMove(bLegal, bQxnt);
State.MonitorBound(this); // Pass position so heartbeat() can build getCurrentMoves()
return(bLegal);
}
protected void findRepetition()
{
GameState.AtomicIncrement(ref State.RepetitionSearches);
clrRepetition();
if (IsDraw0())
{
return;
}
var bNullMade = IsNullMade();
//
//[Note]This search for 3-fold repetition extends to the initial position;
// not just to State.MovePosition where the current search began.
//
for (var position = Parent; position is not null; position = position.Parent)
{
GameState.AtomicIncrement(ref State.RepetitionPlies);
//
// Include Positions for both sides, stopping when the Transposition Group ends.
//
if (Equals(position))
{
if (bNullMade)
{
//
// Null Moves do not count as repetition of the position; but the
// Draw3 and Draw2 flags are copied to expedite subsequent search:
//
FlagsDraw |= position.fdr();
}
else
{
setRepetition(position.fdr() != 0);
}
break;
}
else if (position.IsDraw0())
{
break; // End of Transposition Group
}
}
#if DebugDraw2
validateDraw2();
#endif
}
//
// Lazy Capture avoids calling getPieceIndex() until it becomes necessary.
// The purpose of the following method is to update the move and to avoid
// calling getPieceIndex() again.
//
// SaveCapture is required to show captures in AppendAN() if bExpandFrom.
//
protected Byte captureIndex(Int32 nTo, ref Move move, out Boolean bEnPassant)
{
bEnPassant = false;
var vCapture = vPieceNull;
var uCapture = captured(move);
var capture = (Piece)uCapture;
if (capture == Piece.Capture)
{
#if CountCapturedPiece
GameState.AtomicIncrement(ref State.CapturedPieceTotal);
#endif
//
// Between 2% and 20% of all Pseudo Moves require a call to getPieceIndex().
// At the rate of 72 MHz when a Pawn is found; 68 MHz otherwise, the 1.5%
// cost would be quite low even were it incurred for every generated move.
//
vCapture = getPieceIndex(nTo);
Debug.Assert(vCapture != vPieceNull, "vCapture == vPieceNull",
$"There is no piece to capture on {(sq)nTo}.");
#if SaveCapture
var captive = indexPiece(vCapture);
move &= ~Move.CaptiveMask;
move |= (Move)((UInt32)captive << nCaptiveBit);
#endif
}
else if (capture == Piece.EP)
{
bEnPassant = true;
vCapture = vP6;
}
else if (capture == Piece.None)
{
Debug.Assert(capture != Piece.None, "Unexpected Non-Capture");
}
else
{
vCapture = pieceIndex(uCapture);
}
Debug.Assert(vCapture != vK6, "Unknown Captive",
$"No captive found for {(sq)nTo}.");
return(vCapture);
}
protected Eval final()
{
//
// The game is over if the side to move has no move.
// If the King is in Check, this is a Checkmate and
// the lowest possible evaluation is given.
//
if (InCheck())
{
GameState.AtomicIncrement(ref State.MateTotal);
return(debitMate(-MateMax, SearchPly));
}
//
// If the King is not in Check, this is a Stalemate
// and an equal evaluation is returned.
//
var bWTM = WTM();
var mValue = contempt();
return(reflectValue(bWTM, mValue));
}
protected Boolean nullMove()
{
CurrentMove = Move.NullMove; // Current Pseudo Move
resetMove();
skipTurn();
//[Note]If En Passant was possible, any move ends a Transposition Group
if (Parent.IsPassed())
{
setDraw0();
}
testHash(); // Conditional
var bLegal = !InCheck();
if (!bLegal)
{
throw new BoardException("Illegal Null Move");
}
GameState.AtomicIncrement(ref State.NullMoveTotal);
State.MonitorBound(this);
return(bLegal);
}
private Eval fullEval()
{
//
//[Note]StaticEvaluations = TotalEvaluations - FullEvaluations
// Draws are included; because they exit early.
//
GameState.AtomicIncrement(ref State.FullEvals);
var mValue = staticEval(out PawnPosition pp);
//
// Load PawnFeature Deltas from the PawnPositions hash table,
// based on HashPawn, the Zobrist Hashcode summed over Pawns.
//
if (Pawn == 0) // PawnHash == default(Hashcode)}
{
#if EvalKBNvKMateCorner
if ((FlagsEG & EGFlags.KBNvK) != 0)
{
var mReward = rewardKBNvKMateCorner();
mValue += mReward;
}
#endif
}
else
{
#if EvalOutsideSquare
if ((FlagsEG & EGFlags.OutsideSquare) != 0)
{
var mReward = punishOutsideSquare();
mValue += mReward;
}
#endif
#if EvalKQvKPDistance
if ((FlagsEG & EGFlags.KQvKP) != 0)
{
var mReward = rewardKQvKPProximity();
mValue += mReward;
}
#endif
#if EvalRookBehindPasser
if (Rook != 0)
{
#if PawnPositionByValue
var bDefault = (pp.BlackPRP & PRPFlags.IsValid) == 0;
#else
var bDefault = pp == default(PawnPosition);
#endif
if (bDefault)
{
pp = State.GetPXP(this);
}
const Boolean bWhiteRook = true;
var mRooksBehindBlack = rookBehindPasser(!bWhiteRook, pp.BlackPassers);
var mRooksBehindWhite = rookBehindPasser(bWhiteRook, pp.WhitePassers);
#if TestRookBehindPasser
if (mRooksBehindBlack != 0 ||
mRooksBehindWhite != 0)
{
DisplayCurrent("pieceval()");
}
#endif
mValue += mRooksBehindWhite;
mValue -= mRooksBehindBlack;
}
#endif
}
var mAbs = Abs(mValue);
Debug.Assert(mAbs < MateMin, "Mate value returned by staticEval()");
if (mAbs <= mDeltaBaseWeight) //[ToDo]Define a new threshold
{
#if BuildAtxTo
buildAtxTo(RankPiece);
#endif
#if Mobility
mValue += mobility();
#endif
}
//
// The following helps find Draw3
//
if (IsDraw2() && mAbs < MateMin)
{
mValue /= 4; //[IBV]Care will be needed to protect the EvalType here
}
return(mValue);
}
//
//[ToDo]Add evaluation of practical Draws where helpmate is possible:
//
// KKNN or KNKNN
// KBKB opposite color
// KNKBN, KBKBN. KBKBB pair [Note: KNKBB pair can be won; but perhaps not in 50 moves]
//
// More Complex Draws, assuming weaker side in time to defend:
//
// KKP if weaker side maintains opposition
// Distant Opposition vs. Key/Critical Squares vs Corresponding or Relative Squares!?
//
// KBKBP of opposite color
// KPKQ if P to queen on ACFH-file and sronger K too far to help
//
//
// Development [initial move per piece, delaying heavy pieces]
// Control of the Center by Pawns
// Control of Squares around King
// Castling and King Safety [Corner Squares] vs King Activity in the Endgame
//
// Rooks on Open Files
// Rook or Queen on 7th [or 2nd] Rank
// Protected Piece and Connected Rook Bonus
// Knight Scope and Outpost [free of Pawn harrassment]
// Bishop Scope [and Bad Bishop Detection]
//
// Bonus for Bishop with color of Promotion Square for any Passed Pawns, especially
// Rook Pawns. Applies to defense and Passed Opposing Pawns, as well as to offense.
//
// Attack Pawn Chains at the base
// Bonus for Passed Pawn Couples
//
// Piece Values depending on Opening, Middle, End Game Phase and Relative Advantage:
// Stronger side favors [vice versa Weaker side is averse to]
// Bishops of Opposite Colors in Middle Game; and Bishops of Same Color in Endgame.
//
//
// Technical and Tablebase Draws:
// KRKRP if weaker side can attain Philidor Position
//
// EGTB Alternatives: Syzygy by Ronald de Man, Gaviota EGTB by Miguel A. Ballicora,
// Nalimov by Eugene Nalimov. Syzygy is preferred by Houdini. It is compact; but
// does not provide Distance to Mate (DTM). They provide Wind-Draw-Loss (WDL) and
// Distance to Zero (DTZ).
//
// The Syzygy 6-man EGTB is available at http://tablebase.sesse.net/syzygy, where
// the (290) 3-4-5-men files require 938 MB; and (730) 6-men files require 149 GB.
//
protected Eval staticEval(out PawnPosition pp) //[New]~9.666 MHz vs ~13.333 MHz w/o EvalRookBehindPasser
{
pp = default;
if (IsInsufficient())
{
return(contempt());
}
GameState.AtomicIncrement(ref State.TotalEvals); // vs. FullEvaluations
setEndGameFlags();
if (EvalUndefined < StaticDelta)
{
return(StaticDelta);
}
//
// Retrieve material balance from the Composition:
//
getValue(out Eval mDelta, out Eval mTotal);
if (Pawn != 0) // Else PawnHash == default(Hashcode)
{
pp = State.GetPXP(this);
mDelta += pp.Delta;
mTotal += pp.Total;
#if EvalWrongBishop
if (punishWrongBishop(pp.BlackPRP & PRPFlags.Both, Side[Black].FlagsHi))
{
mDelta += mWrongBishopWeight; // Black has Wrong Bishop
}
if (punishWrongBishop(pp.WhitePRP & PRPFlags.Both, Side[White].FlagsHi))
{
mDelta -= mWrongBishopWeight; // White has Wrong Bishop
}
#endif
}
#if TradePieces
if (mTotal > 0)
{
//
// The following provides an incentive for the stronger
// side to exchange material and for the weaker side to
// avoid such exchanges. The value is Zero in an equal
// position, and grows to a maximum of one centipawn if
// the weaker side has been stripped of all material.
//
// Intuitively: Exchanges reduce the Total material but
// leave the Delta unaffected; and Delta can range from
// Zero to the Total. Thus, their quotient ranges from
// Zero to One.
//
//[Note]A refinement is needed to prefer trading Pieces
// over Pawns in the endgame.
//
var mIncentive = (Eval)(mPawnWeight * mDelta / mTotal);
mDelta += mIncentive;
}
#endif
//
//[Note]staticEval() prepares StaticTotal for any isEndgame() tests
//
StaticTotal = mTotal; // Update for isEndgame()
StaticDelta = mDelta;
return(mDelta);
}