feat(eval): add tapered piece-square evaluation
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dualfroz committed
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package gambit
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object Eval:
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val pieceValue: Array[Int] = Array(0, 100, 320, 330, 500, 900, 20000)
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private val mgValue = Array(0, 100, 320, 330, 500, 900, 0)
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private val egValue = Array(0, 120, 320, 330, 540, 940, 0)
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private val phaseWeight = Array(0, 0, 1, 1, 2, 4, 0)
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private val maxPhase = 24
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private val pawnMg = Array(
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0, 0, 0, 0, 0, 0, 0, 0,
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50, 50, 50, 50, 50, 50, 50, 50,
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10, 10, 20, 30, 30, 20, 10, 10,
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5, 5, 10, 25, 25, 10, 5, 5,
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0, 0, 0, 20, 20, 0, 0, 0,
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5, -5, -10, 0, 0, -10, -5, 5,
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5, 10, 10, -20, -20, 10, 10, 5,
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0, 0, 0, 0, 0, 0, 0, 0
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)
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private val pawnEg = Array(
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0, 0, 0, 0, 0, 0, 0, 0,
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80, 80, 80, 80, 80, 80, 80, 80,
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50, 50, 50, 50, 50, 50, 50, 50,
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30, 30, 30, 30, 30, 30, 30, 30,
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20, 20, 20, 20, 20, 20, 20, 20,
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10, 10, 10, 10, 10, 10, 10, 10,
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10, 10, 10, 10, 10, 10, 10, 10,
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0, 0, 0, 0, 0, 0, 0, 0
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)
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private val knightTable = Array(
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-50, -40, -30, -30, -30, -30, -40, -50,
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-40, -20, 0, 0, 0, 0, -20, -40,
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-30, 0, 10, 15, 15, 10, 0, -30,
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-30, 5, 15, 20, 20, 15, 5, -30,
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-30, 0, 15, 20, 20, 15, 0, -30,
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-30, 5, 10, 15, 15, 10, 5, -30,
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-40, -20, 0, 5, 5, 0, -20, -40,
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-50, -40, -30, -30, -30, -30, -40, -50
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)
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private val bishopTable = Array(
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-20, -10, -10, -10, -10, -10, -10, -20,
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-10, 0, 0, 0, 0, 0, 0, -10,
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-10, 0, 5, 10, 10, 5, 0, -10,
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-10, 5, 5, 10, 10, 5, 5, -10,
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-10, 0, 10, 10, 10, 10, 0, -10,
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-10, 10, 10, 10, 10, 10, 10, -10,
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-10, 5, 0, 0, 0, 0, 5, -10,
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-20, -10, -10, -10, -10, -10, -10, -20
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)
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private val rookTable = Array(
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0, 0, 0, 0, 0, 0, 0, 0,
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5, 10, 10, 10, 10, 10, 10, 5,
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-5, 0, 0, 0, 0, 0, 0, -5,
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-5, 0, 0, 0, 0, 0, 0, -5,
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-5, 0, 0, 0, 0, 0, 0, -5,
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-5, 0, 0, 0, 0, 0, 0, -5,
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-5, 0, 0, 0, 0, 0, 0, -5,
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0, 0, 0, 5, 5, 0, 0, 0
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)
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private val queenTable = Array(
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-20, -10, -10, -5, -5, -10, -10, -20,
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-10, 0, 0, 0, 0, 0, 0, -10,
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-10, 0, 5, 5, 5, 5, 0, -10,
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-5, 0, 5, 5, 5, 5, 0, -5,
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0, 0, 5, 5, 5, 5, 0, -5,
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-10, 5, 5, 5, 5, 5, 0, -10,
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-10, 0, 5, 0, 0, 0, 0, -10,
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-20, -10, -10, -5, -5, -10, -10, -20
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)
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private val kingMg = Array(
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-30, -40, -40, -50, -50, -40, -40, -30,
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-30, -40, -40, -50, -50, -40, -40, -30,
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-30, -40, -40, -50, -50, -40, -40, -30,
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-30, -40, -40, -50, -50, -40, -40, -30,
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-20, -30, -30, -40, -40, -30, -30, -20,
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-10, -20, -20, -20, -20, -20, -20, -10,
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20, 20, 0, 0, 0, 0, 20, 20,
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20, 30, 10, 0, 0, 10, 30, 20
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)
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private val kingEg = Array(
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-50, -40, -30, -20, -20, -30, -40, -50,
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-30, -20, -10, 0, 0, -10, -20, -30,
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-30, -10, 20, 30, 30, 20, -10, -30,
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-30, -10, 30, 40, 40, 30, -10, -30,
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-30, -10, 30, 40, 40, 30, -10, -30,
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-30, -10, 20, 30, 30, 20, -10, -30,
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-30, -30, 0, 0, 0, 0, -30, -30,
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-50, -30, -30, -30, -30, -30, -30, -50
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)
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private val mgTables = Array(null, pawnMg, knightTable, bishopTable, rookTable, queenTable, kingMg)
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private val egTables = Array(null, pawnEg, knightTable, bishopTable, rookTable, queenTable, kingEg)
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private val passedMg = Array(0, 8, 16, 28, 48, 78, 120, 0)
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private val passedEg = Array(0, 18, 30, 52, 90, 140, 210, 0)
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private val doubledPenalty = 14
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private val isolatedPenalty = 12
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private val bishopPairBonus = 32
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private val rookOpenBonus = 22
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private val rookSemiOpenBonus = 11
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private val mobilityWeight = Array(0, 0, 4, 5, 3, 2, 0)
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private val shieldBonus = 9
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private val ringAttackPenalty = 8
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inline private def pstIndex(color: Int, sq: Int): Int =
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if color == Color.White then (7 - Square.rankOf(sq)) * 8 + Square.fileOf(sq)
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else Square.rankOf(sq) * 8 + Square.fileOf(sq)
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def evaluate(pos: Position): Int =
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val board = pos.board
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val pawns = Array(0L, 0L)
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val bishops = Array(0, 0)
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var mg = 0
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var eg = 0
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var phase = 0
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var flat = 0
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var sq = 0
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while sq < 128 do
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if Square.onBoard(sq) then
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val p = board(sq)
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if p != Piece.Empty then
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val pieceType = p & 7
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val color = p >> 3
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val idx = pstIndex(color, sq)
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val mgTerm = mgValue(pieceType) + mgTables(pieceType)(idx)
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val egTerm = egValue(pieceType) + egTables(pieceType)(idx)
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phase += phaseWeight(pieceType)
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if color == Color.White then
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mg += mgTerm
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eg += egTerm
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else
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mg -= mgTerm
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eg -= egTerm
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pieceType match
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case Piece.Pawn => pawns(color) |= Bitboards.bit(Bitboards.sq64(sq))
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case Piece.Bishop => bishops(color) += 1
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case _ => ()
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sq += 1
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flat += mobility(pos, Color.White) - mobility(pos, Color.Black)
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flat += kingSafety(pos, Color.White) - kingSafety(pos, Color.Black)
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if bishops(Color.White) >= 2 then flat += bishopPairBonus
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if bishops(Color.Black) >= 2 then flat -= bishopPairBonus
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flat += rookFiles(pos, Color.White, pawns) - rookFiles(pos, Color.Black, pawns)
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val (pawnMgTerm, pawnEgTerm) = pawnStructure(pawns)
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mg += pawnMgTerm + flat
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eg += pawnEgTerm + flat
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val boundedPhase = if phase > maxPhase then maxPhase else phase
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val blended = (mg * boundedPhase + eg * (maxPhase - boundedPhase)) / maxPhase
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if pos.sideToMove == Color.White then blended else -blended
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private def pawnStructure(pawns: Array[Long]): (Int, Int) =
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var mg = 0
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var eg = 0
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var color = 0
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while color < 2 do
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val sign = if color == Color.White then 1 else -1
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val own = pawns(color)
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val enemy = pawns(color ^ 1)
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var f = 0
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while f < 8 do
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val onFile = Bitboards.count(own & Bitboards.fileMask(f))
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if onFile > 1 then
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mg -= sign * doubledPenalty * (onFile - 1)
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eg -= sign * doubledPenalty * (onFile - 1)
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if onFile > 0 && (own & Bitboards.adjacentFiles(f)) == 0L then
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mg -= sign * isolatedPenalty * onFile
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eg -= sign * isolatedPenalty * onFile
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f += 1
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var bb = own
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while bb != 0L do
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val s = java.lang.Long.numberOfTrailingZeros(bb)
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bb &= bb - 1
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val ahead = if color == Color.White then Bitboards.passedWhite(s) else Bitboards.passedBlack(s)
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if (ahead & enemy) == 0L then
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val relRank = if color == Color.White then Bitboards.rankOf(s) else 7 - Bitboards.rankOf(s)
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mg += sign * passedMg(relRank)
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eg += sign * passedEg(relRank)
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color += 1
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(mg, eg)
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private def mobility(pos: Position, color: Int): Int =
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val board = pos.board
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var total = 0
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var sq = 0
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while sq < 128 do
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if Square.onBoard(sq) then
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val p = board(sq)
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if p != Piece.Empty && (p >> 3) == color then
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val pt = p & 7
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pt match
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case Piece.Knight => total += stepCount(board, sq, color, Directions.knight) * mobilityWeight(pt)
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case Piece.Bishop => total += slideCount(board, sq, color, Directions.bishop) * mobilityWeight(pt)
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case Piece.Rook => total += slideCount(board, sq, color, Directions.rook) * mobilityWeight(pt)
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case Piece.Queen =>
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val q = slideCount(board, sq, color, Directions.bishop) + slideCount(board, sq, color, Directions.rook)
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total += q * mobilityWeight(pt)
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case _ => ()
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sq += 1
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total
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private def stepCount(board: Array[Int], sq: Int, color: Int, offsets: Array[Int]): Int =
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var c = 0
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var i = 0
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while i < offsets.length do
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val t = sq + offsets(i)
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if Square.onBoard(t) && (board(t) == Piece.Empty || (board(t) >> 3) != color) then c += 1
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i += 1
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c
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private def slideCount(board: Array[Int], sq: Int, color: Int, offsets: Array[Int]): Int =
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var c = 0
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var i = 0
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while i < offsets.length do
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var t = sq + offsets(i)
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var stop = false
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while Square.onBoard(t) && !stop do
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val tp = board(t)
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if tp == Piece.Empty then
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c += 1
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t += offsets(i)
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else
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if (tp >> 3) != color then c += 1
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stop = true
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i += 1
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c
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private def kingSafety(pos: Position, color: Int): Int =
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val kingSq = pos.kingSquare(color)
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val enemy = color ^ 1
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val board = pos.board
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var score = 0
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val forward = if color == Color.White then 16 else -16
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val ownPawn = Piece.make(color, Piece.Pawn)
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var d = -1
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while d <= 1 do
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val shieldSq = kingSq + forward + d
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if Square.onBoard(shieldSq) && board(shieldSq) == ownPawn then score += shieldBonus
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val shieldSq2 = kingSq + forward * 2 + d
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if Square.onBoard(shieldSq2) && board(shieldSq2) == ownPawn then score += shieldBonus / 2
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d += 1
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var attackers = 0
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var i = 0
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while i < Directions.king.length do
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val ring = kingSq + Directions.king(i)
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if Square.onBoard(ring) && pos.isAttacked(ring, enemy) then attackers += 1
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i += 1
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score - attackers * ringAttackPenalty
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private def rookFiles(pos: Position, color: Int, pawns: Array[Long]): Int =
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val board = pos.board
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val rook = Piece.make(color, Piece.Rook)
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var score = 0
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var sq = 0
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while sq < 128 do
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if Square.onBoard(sq) && board(sq) == rook then
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val f = Square.fileOf(sq)
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val own = pawns(color) & Bitboards.fileMask(f)
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val enemy = pawns(color ^ 1) & Bitboards.fileMask(f)
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if own == 0L && enemy == 0L then score += rookOpenBonus
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else if own == 0L then score += rookSemiOpenBonus
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sq += 1
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score
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