private static int CalculatePawnScores(ChessBoard cb)
{
var score = 0;
// penalty for doubled pawns
for (var i = 0; i < 8; i++)
{
if (BitOperations.PopCount((ulong)(cb.Pieces[White][Pawn] & Bitboard.Files[i])) > 1)
{
score -= EvalConstants.PawnScores[EvalConstants.IxPawnDouble];
}
if (BitOperations.PopCount((ulong)(cb.Pieces[Black][Pawn] & Bitboard.Files[i])) > 1)
{
score += EvalConstants.PawnScores[EvalConstants.IxPawnDouble];
}
}
// bonus for connected pawns
var pawns = Bitboard.GetWhitePawnAttacks(cb.Pieces[White][Pawn]) & cb.Pieces[White][Pawn];
while (pawns != 0)
{
score += EvalConstants.PawnConnected[BitOperations.TrailingZeroCount(pawns) / 8];
pawns &= pawns - 1;
}
pawns = Bitboard.GetBlackPawnAttacks(cb.Pieces[Black][Pawn]) & cb.Pieces[Black][Pawn];
while (pawns != 0)
{
score -= EvalConstants.PawnConnected[7 - BitOperations.TrailingZeroCount(pawns) / 8];
pawns &= pawns - 1;
}
// bonus for neighbour pawns
pawns = Bitboard.GetPawnNeighbours(cb.Pieces[White][Pawn]) & cb.Pieces[White][Pawn];
while (pawns != 0)
{
score += EvalConstants.PawnNeighbour[BitOperations.TrailingZeroCount(pawns) / 8];
pawns &= pawns - 1;
}
pawns = Bitboard.GetPawnNeighbours(cb.Pieces[Black][Pawn]) & cb.Pieces[Black][Pawn];
while (pawns != 0)
{
score -= EvalConstants.PawnNeighbour[7 - BitOperations.TrailingZeroCount(pawns) / 8];
pawns &= pawns - 1;
}
// set outposts
cb.PassedPawnsAndOutposts = 0;
pawns = Bitboard.GetWhitePawnAttacks(cb.Pieces[White][Pawn]) & ~cb.Pieces[White][Pawn] &
~cb.Pieces[Black][Pawn];
while (pawns != 0)
{
if ((Bitboard.GetWhiteAdjacentMask(BitOperations.TrailingZeroCount(pawns)) & cb.Pieces[Black][Pawn]) ==
0)
{
cb.PassedPawnsAndOutposts |= pawns & -pawns;
}
pawns &= pawns - 1;
}
pawns = Bitboard.GetBlackPawnAttacks(cb.Pieces[Black][Pawn]) & ~cb.Pieces[White][Pawn] &
~cb.Pieces[Black][Pawn];
while (pawns != 0)
{
if ((Bitboard.GetBlackAdjacentMask(BitOperations.TrailingZeroCount(pawns)) & cb.Pieces[White][Pawn]) ==
0)
{
cb.PassedPawnsAndOutposts |= pawns & -pawns;
}
pawns &= pawns - 1;
}
int index;
// white
pawns = cb.Pieces[White][Pawn];
while (pawns != 0)
{
index = BitOperations.TrailingZeroCount(pawns);
// isolated pawns
if ((Bitboard.FilesAdjacent[index & 7] & cb.Pieces[White][Pawn]) == 0)
{
score -= EvalConstants.PawnScores[EvalConstants.IxPawnIsolated];
}
// backward pawns
else if ((Bitboard.GetBlackAdjacentMask(index + 8) & cb.Pieces[White][Pawn]) == 0)
{
if ((StaticMoves.PawnAttacks[White][index + 8] & cb.Pieces[Black][Pawn]) != 0)
{
if ((Bitboard.Files[index & 7] & cb.Pieces[Black][Pawn]) == 0)
{
score -= EvalConstants.PawnScores[EvalConstants.IxPawnBackward];
}
}
}
// pawn defending 2 pawns
if (BitOperations.PopCount((ulong)(StaticMoves.PawnAttacks[White][index] & cb.Pieces[White][Pawn])) ==
2)
{
score -= EvalConstants.PawnScores[EvalConstants.IxPawnInverse];
}
// set passed pawns
if ((Bitboard.GetWhitePassedPawnMask(index) & cb.Pieces[Black][Pawn]) == 0)
{
cb.PassedPawnsAndOutposts |= pawns & -pawns;
}
// candidate passed pawns (no pawns in front, more friendly pawns behind and adjacent than enemy pawns)
else if (63 - BitOperations.LeadingZeroCount(
(ulong)((cb.Pieces[White][Pawn] | cb.Pieces[Black][Pawn]) &
Bitboard.Files[index & 7])) == index)
{
if (BitOperations.PopCount((ulong)(cb.Pieces[White][Pawn] &
Bitboard.GetBlackPassedPawnMask(index + 8))) >=
BitOperations.PopCount(
(ulong)(cb.Pieces[Black][Pawn] & Bitboard.GetWhitePassedPawnMask(index))))
{
score += EvalConstants.PassedCandidate[index / 8];
}
}
pawns &= pawns - 1;
}
// black
pawns = cb.Pieces[Black][Pawn];
while (pawns != 0)
{
index = BitOperations.TrailingZeroCount(pawns);
// isolated pawns
if ((Bitboard.FilesAdjacent[index & 7] & cb.Pieces[Black][Pawn]) == 0)
{
score += EvalConstants.PawnScores[EvalConstants.IxPawnIsolated];
}
// backward pawns
else if ((Bitboard.GetWhiteAdjacentMask(index - 8) & cb.Pieces[Black][Pawn]) == 0)
{
if ((StaticMoves.PawnAttacks[Black][index - 8] & cb.Pieces[White][Pawn]) != 0)
{
if ((Bitboard.Files[index & 7] & cb.Pieces[White][Pawn]) == 0)
{
score += EvalConstants.PawnScores[EvalConstants.IxPawnBackward];
}
}
}
// pawn defending 2 pawns
if (BitOperations.PopCount((ulong)(StaticMoves.PawnAttacks[Black][index] & cb.Pieces[Black][Pawn])) ==
2)
{
score += EvalConstants.PawnScores[EvalConstants.IxPawnInverse];
}
// set passed pawns
if ((Bitboard.GetBlackPassedPawnMask(index) & cb.Pieces[White][Pawn]) == 0)
{
cb.PassedPawnsAndOutposts |= pawns & -pawns;
}
// candidate passers
else if (BitOperations.TrailingZeroCount((cb.Pieces[White][Pawn] | cb.Pieces[Black][Pawn]) &
Bitboard.Files[index & 7]) == index)
{
if (BitOperations.PopCount((ulong)(cb.Pieces[Black][Pawn] &
Bitboard.GetWhitePassedPawnMask(index - 8))) >=
BitOperations.PopCount(
(ulong)(cb.Pieces[White][Pawn] & Bitboard.GetBlackPassedPawnMask(index))))
{
score -= EvalConstants.PassedCandidate[7 - index / 8];
}
}
pawns &= pawns - 1;
}
return(score);
}
