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⚖️ Pawn phalanx #1009

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merged 6 commits into from
Sep 15, 2024
Merged

⚖️ Pawn phalanx #1009

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439a744
Implement pawn phalanx by rank
eduherminio Sep 14, 2024
21050e2
Add tuned values
eduherminio Sep 14, 2024
db6c5a1
Merge with main
eduherminio Sep 15, 2024
673337d
Fix merge
eduherminio Sep 15, 2024
5e72fd8
Add tmp params
eduherminio Sep 15, 2024
7f55356
Add values tuned at 10k
eduherminio Sep 15, 2024
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33 changes: 30 additions & 3 deletions src/Lynx/Model/Position.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -532,8 +532,11 @@ public bool WasProduceByAValidMove()
int packedScore = 0;
int gamePhase = 0;

BitBoard whitePawnAttacks = PieceBitBoards[(int)Piece.P].ShiftUpRight() | PieceBitBoards[(int)Piece.P].ShiftUpLeft();
BitBoard blackPawnAttacks = PieceBitBoards[(int)Piece.p].ShiftDownRight() | PieceBitBoards[(int)Piece.p].ShiftDownLeft();
var whitePawns = PieceBitBoards[(int)Piece.P];
var blackPawns = PieceBitBoards[(int)Piece.p];

BitBoard whitePawnAttacks = whitePawns.ShiftUpRight() | whitePawns.ShiftUpLeft();
BitBoard blackPawnAttacks = blackPawns.ShiftDownRight() | blackPawns.ShiftDownLeft();

var whiteKing = PieceBitBoards[(int)Piece.K].GetLS1BIndex();
var blackKing = PieceBitBoards[(int)Piece.k].GetLS1BIndex();
Expand Down Expand Up @@ -590,6 +593,30 @@ public bool WasProduceByAValidMove()
packedScore -= BishopPairBonus;
}

// Pawn phalanx
var whitePawnsRight = whitePawns.ShiftRight();
var whitePhalanx = whitePawns & whitePawnsRight;
while (whitePhalanx != 0)
{
var square = whitePhalanx.GetLS1BIndex();
whitePhalanx.ResetLS1B();

var rank = Constants.Rank[square];
packedScore += PawnPhalanxBonus[rank];
}

var blackPawnsRight = blackPawns.ShiftRight();
var blackPhalanx = blackPawns & blackPawnsRight;
while (blackPhalanx != 0)
{
var square = blackPhalanx.GetLS1BIndex();
blackPhalanx.ResetLS1B();

var rank = 7 - Constants.Rank[square];
packedScore -= PawnPhalanxBonus[rank];
}


// Pieces protected by pawns bonus
packedScore += PieceProtectedByPawnBonus
* ((whitePawnAttacks & OccupancyBitBoards[(int)Side.White] /*& (~PieceBitBoards[(int)Piece.P])*/).CountBits()
Expand All @@ -613,7 +640,7 @@ public bool WasProduceByAValidMove()
gamePhase = maxPhase;
}

int totalPawnsCount = PieceBitBoards[(int)Piece.P].CountBits() + PieceBitBoards[(int)Piece.p].CountBits();
int totalPawnsCount = whitePawns.CountBits() + blackPawns.CountBits();

// Pawnless endgames with few pieces
if (gamePhase <= 3 && totalPawnsCount == 0)
Expand Down
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