/// probe() takes a position object as input, computes a Entry object, and returns
/// a pointer to it. The result is also stored in a hash table, so we don't have
/// to recompute everything when the same pawn structure occurs again.
public static Pawns.Entry probe(Position pos, Pawns.Table entries)
{
Key key = pos.pawn_key();
Pawns.Entry e = entries[key];
if (e.key == key)
{
return(e);
}
e.key = key;
e.value = evaluate(pos, e, ColorS.WHITE) - evaluate(pos, e, ColorS.BLACK);
return(e);
}
public static Score evaluate(Position pos, Pawns.Entry e, Color Us)
{
Color Them = (Us == ColorS.WHITE ? ColorS.BLACK : ColorS.WHITE);
Square Up = (Us == ColorS.WHITE ? SquareS.DELTA_N : SquareS.DELTA_S);
Square Right = (Us == ColorS.WHITE ? SquareS.DELTA_NE : SquareS.DELTA_SW);
Square Left = (Us == ColorS.WHITE ? SquareS.DELTA_NW : SquareS.DELTA_SE);
Bitboard b, p, doubled;
Square s;
File f;
Rank r;
bool passed, isolated, opposed, connected, backward, candidate, unsupported;
Score value = ScoreS.SCORE_ZERO;
Square[] pl = pos.list(Us, PieceTypeS.PAWN);
int plPos = 0;
Bitboard ourPawns = pos.pieces_color_piecetype(Us, PieceTypeS.PAWN);
Bitboard theirPawns = pos.pieces_color_piecetype(Them, PieceTypeS.PAWN);
e.passedPawns[Us] = e.candidatePawns[Us] = 0;
e.kingSquares[Us] = SquareS.SQ_NONE;
e.semiopenFiles[Us] = 0xFF;
e.pawnAttacks[Us] = BitBoard.shift_bb(ourPawns, Right) | BitBoard.shift_bb(ourPawns, Left);
e.pawnsOnSquares[Us][ColorS.BLACK] = Bitcount.popcount_Max15(ourPawns & BitBoard.DarkSquares);
e.pawnsOnSquares[Us][ColorS.WHITE] = pos.count(Us, PieceTypeS.PAWN) - e.pawnsOnSquares[Us][ColorS.BLACK];
// Loop through all pawns of the current color and score each pawn
while ((s = pl[plPos++]) != SquareS.SQ_NONE)
{
Debug.Assert(pos.piece_on(s) == Types.make_piece(Us, PieceTypeS.PAWN));
f = Types.file_of(s);
// This file cannot be semi-open
e.semiopenFiles[Us] &= ~(1 << f);
// Previous rank
p = BitBoard.rank_bb_square(s - Types.pawn_push(Us));
// Our rank plus previous one
b = BitBoard.rank_bb_square(s) | p;
// Flag the pawn as passed, isolated, doubled,
// unsupported or connected (but not the backward one).
connected = (ourPawns & BitBoard.adjacent_files_bb(f) & b) != 0;
unsupported = (0 == (ourPawns & BitBoard.adjacent_files_bb(f) & p));
isolated = (0 == (ourPawns & BitBoard.adjacent_files_bb(f)));
doubled = ourPawns & BitBoard.forward_bb(Us, s);
opposed = (theirPawns & BitBoard.forward_bb(Us, s)) != 0;
passed = (0 == (theirPawns & BitBoard.passed_pawn_mask(Us, s)));
// Test for backward pawn.
// If the pawn is passed, isolated, or connected it cannot be
// backward. If there are friendly pawns behind on adjacent files
// or if it can capture an enemy pawn it cannot be backward either.
if ((passed | isolated | connected) ||
(ourPawns & BitBoard.pawn_attack_span(Them, s)) != 0 ||
(pos.attacks_from_pawn(s, Us) & theirPawns) != 0)
{
backward = false;
}
else
{
// We now know that there are no friendly pawns beside or behind this
// pawn on adjacent files. We now check whether the pawn is
// backward by looking in the forward direction on the adjacent
// files, and picking the closest pawn there.
b = BitBoard.pawn_attack_span(Us, s) & (ourPawns | theirPawns);
b = BitBoard.pawn_attack_span(Us, s) & BitBoard.rank_bb_square(BitBoard.backmost_sq(Us, b));
// If we have an enemy pawn in the same or next rank, the pawn is
// backward because it cannot advance without being captured.
backward = ((b | BitBoard.shift_bb(b, Up)) & theirPawns) != 0;
}
Debug.Assert(opposed | passed | (BitBoard.pawn_attack_span(Us, s) & theirPawns) != 0);
// A not-passed pawn is a candidate to become passed, if it is free to
// advance and if the number of friendly pawns beside or behind this
// pawn on adjacent files is higher than or equal to the number of
// enemy pawns in the forward direction on the adjacent files.
candidate = !(opposed | passed | backward | isolated) &&
(b = BitBoard.pawn_attack_span(Them, s + Types.pawn_push(Us)) & ourPawns) != 0 &&
Bitcount.popcount_Max15(b) >= Bitcount.popcount_Max15(BitBoard.pawn_attack_span(Us, s) & theirPawns);
// Passed pawns will be properly scored in evaluation because we need
// full attack info to evaluate passed pawns. Only the frontmost passed
// pawn on each file is considered a true passed pawn.
if (passed && 0 == doubled)
{
e.passedPawns[Us] |= BitBoard.SquareBB[s];
}
// Score this pawn
if (isolated)
{
value -= Isolated[opposed ? 1 : 0][f];
}
if (unsupported && !isolated)
{
value -= UnsupportedPawnPenalty;
}
if (doubled != 0)
{
value -= Types.divScore(Doubled[f], BitBoard.rank_distance(s, BitBoard.lsb(doubled)));
}
if (backward)
{
value -= Backward[opposed ? 1 : 0][f];
}
if (connected)
{
value += Connected[f][Types.relative_rank_square(Us, s)];
}
if (candidate)
{
value += CandidatePassed[Types.relative_rank_square(Us, s)];
if (0 == doubled)
{
e.candidatePawns[Us] |= BitBoard.SquareBB[s];
}
}
}
// In endgame it's better to have pawns on both wings. So give a bonus according
// to file distance between left and right outermost pawns.
if (pos.count(Us, PieceTypeS.PAWN) > 1)
{
b = (Bitboard)(e.semiopenFiles[Us] ^ 0xFF);
value += PawnsFileSpan * (BitBoard.msb(b) - BitBoard.lsb(b));
}
return(value);
}
