/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
- Copyright (C) 2008-2012 Marco Costalba, Joona Kiiski, Tord Romstad
+ Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
+#include <algorithm>
#include <cassert>
#include "bitboard.h"
namespace {
+ #define V Value
#define S(mg, eg) make_score(mg, eg)
- // Doubled pawn penalty by opposed flag and file
- const Score DoubledPawnPenalty[2][8] = {
- { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
- S(23, 48), S(23, 48), S(20, 48), S(13, 43) },
- { S(13, 43), S(20, 48), S(23, 48), S(23, 48),
- S(23, 48), S(23, 48), S(20, 48), S(13, 43) }};
+ // Doubled pawn penalty by file
+ const Score Doubled[FILE_NB] = {
+ S(13, 43), S(20, 48), S(23, 48), S(23, 48),
+ S(23, 48), S(23, 48), S(20, 48), S(13, 43) };
// Isolated pawn penalty by opposed flag and file
- const Score IsolatedPawnPenalty[2][8] = {
+ const Score Isolated[2][FILE_NB] = {
{ S(37, 45), S(54, 52), S(60, 52), S(60, 52),
S(60, 52), S(60, 52), S(54, 52), S(37, 45) },
{ S(25, 30), S(36, 35), S(40, 35), S(40, 35),
- S(40, 35), S(40, 35), S(36, 35), S(25, 30) }};
+ S(40, 35), S(40, 35), S(36, 35), S(25, 30) } };
// Backward pawn penalty by opposed flag and file
- const Score BackwardPawnPenalty[2][8] = {
+ const Score Backward[2][FILE_NB] = {
{ S(30, 42), S(43, 46), S(49, 46), S(49, 46),
S(49, 46), S(49, 46), S(43, 46), S(30, 42) },
{ S(20, 28), S(29, 31), S(33, 31), S(33, 31),
- S(33, 31), S(33, 31), S(29, 31), S(20, 28) }};
+ S(33, 31), S(33, 31), S(29, 31), S(20, 28) } };
- // Pawn chain membership bonus by file
- const Score ChainBonus[8] = {
- S(11,-1), S(13,-1), S(13,-1), S(14,-1),
- S(14,-1), S(13,-1), S(13,-1), S(11,-1)
- };
+ // Connected pawn bonus by file and rank (initialized by formula)
+ Score Connected[FILE_NB][RANK_NB];
// Candidate passed pawn bonus by rank
- const Score CandidateBonus[8] = {
+ const Score CandidatePassed[RANK_NB] = {
S( 0, 0), S( 6, 13), S(6,13), S(14,29),
- S(34,68), S(83,166), S(0, 0), S( 0, 0)
- };
+ S(34,68), S(83,166), S(0, 0), S( 0, 0) };
- const Score PawnStructureWeight = S(233, 201);
+ // Bonus for file distance of the two outermost pawns
+ const Score PawnsFileSpan = S(0, 15);
- #undef S
+ // Unsupported pawn penalty
+ const Score UnsupportedPawnPenalty = S(20, 10);
- const File ShelterFile[8] = { FILE_B, FILE_B, FILE_C, FILE_D, FILE_E, FILE_F, FILE_G, FILE_G };
+ // Weakness of our pawn shelter in front of the king indexed by [rank]
+ const Value ShelterWeakness[RANK_NB] =
+ { V(100), V(0), V(27), V(73), V(92), V(101), V(101) };
- inline Value score_non_center_file(const Value v) {
- return Value(v * 7 / 16);
- }
+ // Danger of enemy pawns moving toward our king indexed by
+ // [no friendly pawn | pawn unblocked | pawn blocked][rank of enemy pawn]
+ const Value StormDanger[3][RANK_NB] = {
+ { V( 0), V(64), V(128), V(51), V(26) },
+ { V(26), V(32), V( 96), V(38), V(20) },
+ { V( 0), V( 0), V( 64), V(25), V(13) } };
- typedef Value V;
- // Arrays are indexed by rank. Zeroth value is for when no pawn on that file.
- const Value PawnShelter[8] = { V(141), V(0), V( 38), V(102), V(128), V(141), V(141), V(141) };
- const Value PawnStorm[8] = { V( 26), V(0), V(128), V( 51), V( 26), V( 0), V( 0), V( 0) };
- // We compute shelter as a penalty for the given color, but shelter is used as a bonus, so we invert it using this as the basis.
- const Value PawnShelterBasis = PawnShelter[0] + score_non_center_file(PawnShelter[0]) * 2;
+ // Max bonus for king safety. Corresponds to start position with all the pawns
+ // in front of the king and no enemy pawn on the horizon.
+ const Value MaxSafetyBonus = V(263);
- inline Score apply_weight(Score v, Score w) {
- return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
- (int(eg_value(v)) * eg_value(w)) / 0x100);
+ #undef S
+ #undef V
+
+ template<Color Us>
+ Score evaluate(const Position& pos, Pawns::Entry* e) {
+
+ const Color Them = (Us == WHITE ? BLACK : WHITE);
+ const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
+ const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
+ const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
+
+ Bitboard b, p;
+ Square s;
+ File f;
+ bool passed, isolated, doubled, opposed, connected, backward, candidate, unsupported;
+ Score value = SCORE_ZERO;
+ const Square* pl = pos.list<PAWN>(Us);
+
+ Bitboard ourPawns = pos.pieces(Us, PAWN);
+ Bitboard theirPawns = pos.pieces(Them, PAWN);
+
+ e->passedPawns[Us] = e->candidatePawns[Us] = 0;
+ e->kingSquares[Us] = SQ_NONE;
+ e->semiopenFiles[Us] = 0xFF;
+ e->pawnAttacks[Us] = shift_bb<Right>(ourPawns) | shift_bb<Left>(ourPawns);
+ e->pawnsOnSquares[Us][BLACK] = popcount<Max15>(ourPawns & DarkSquares);
+ e->pawnsOnSquares[Us][WHITE] = pos.count<PAWN>(Us) - e->pawnsOnSquares[Us][BLACK];
+
+ // Loop through all pawns of the current color and score each pawn
+ while ((s = *pl++) != SQ_NONE)
+ {
+ assert(pos.piece_on(s) == make_piece(Us, PAWN));
+
+ f = file_of(s);
+
+ // This file cannot be semi-open
+ e->semiopenFiles[Us] &= ~(1 << f);
+
+ // Previous rank
+ p = rank_bb(s - pawn_push(Us));
+
+ // Our rank plus previous one
+ b = rank_bb(s) | p;
+
+ // Flag the pawn as passed, isolated, doubled,
+ // unsupported or connected (but not the backward one).
+ connected = ourPawns & adjacent_files_bb(f) & b;
+ unsupported = !(ourPawns & adjacent_files_bb(f) & p);
+ isolated = !(ourPawns & adjacent_files_bb(f));
+ doubled = ourPawns & forward_bb(Us, s);
+ opposed = theirPawns & forward_bb(Us, s);
+ passed = !(theirPawns & 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 & pawn_attack_span(Them, s))
+ || (pos.attacks_from<PAWN>(s, Us) & theirPawns))
+ 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 = pawn_attack_span(Us, s) & (ourPawns | theirPawns);
+ b = pawn_attack_span(Us, s) & rank_bb(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 | shift_bb<Up>(b)) & theirPawns;
+ }
+
+ assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns));
+
+ // 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 = pawn_attack_span(Them, s + pawn_push(Us)) & ourPawns) != 0
+ && popcount<Max15>(b) >= popcount<Max15>(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 && !doubled)
+ e->passedPawns[Us] |= s;
+
+ // Score this pawn
+ if (isolated)
+ value -= Isolated[opposed][f];
+
+ if (unsupported && !isolated)
+ value -= UnsupportedPawnPenalty;
+
+ if (doubled)
+ value -= Doubled[f];
+
+ if (backward)
+ value -= Backward[opposed][f];
+
+ if (connected)
+ value += Connected[f][relative_rank(Us, s)];
+
+ if (candidate)
+ {
+ value += CandidatePassed[relative_rank(Us, s)];
+
+ if (!doubled)
+ e->candidatePawns[Us] |= 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<PAWN>(Us) > 1)
+ {
+ b = e->semiopenFiles[Us] ^ 0xFF;
+ value += PawnsFileSpan * int(msb(b) - lsb(b));
+ }
+
+ return value;
}
-}
+} // namespace
-/// PawnInfoTable::pawn_info() takes a position object as input, computes
-/// a PawnInfo object, and returns a pointer to it. The result is also stored
-/// in an hash table, so we don't have to recompute everything when the same
-/// pawn structure occurs again.
+namespace Pawns {
-PawnInfo* PawnInfoTable::pawn_info(const Position& pos) const {
+/// init() initializes some tables by formula instead of hard-coding their values
- Key key = pos.pawn_key();
- PawnInfo* pi = probe(key);
+void init() {
+
+ const int bonusesByFile[8] = { 1, 3, 3, 4, 4, 3, 3, 1 };
+ int bonus;
+
+ for (Rank r = RANK_1; r < RANK_8; ++r)
+ for (File f = FILE_A; f <= FILE_H; ++f)
+ {
+ bonus = r * (r-1) * (r-2) + bonusesByFile[f] * (r/2 + 1);
+ Connected[f][r] = make_score(bonus, bonus);
+ }
+}
- // If pi->key matches the position's pawn hash key, it means that we
- // have analysed this pawn structure before, and we can simply return
- // the information we found the last time instead of recomputing it.
- if (pi->key == key)
- return pi;
- // Initialize PawnInfo entry
- pi->key = key;
- pi->passedPawns[WHITE] = pi->passedPawns[BLACK] = 0;
- pi->kingSquares[WHITE] = pi->kingSquares[BLACK] = SQ_NONE;
- pi->halfOpenFiles[WHITE] = pi->halfOpenFiles[BLACK] = 0xFF;
+/// 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.
- // Calculate pawn attacks
- Bitboard wPawns = pos.pieces(PAWN, WHITE);
- Bitboard bPawns = pos.pieces(PAWN, BLACK);
- pi->pawnAttacks[WHITE] = ((wPawns << 9) & ~FileABB) | ((wPawns << 7) & ~FileHBB);
- pi->pawnAttacks[BLACK] = ((bPawns >> 7) & ~FileABB) | ((bPawns >> 9) & ~FileHBB);
+Entry* probe(const Position& pos, Table& entries) {
- // Evaluate pawns for both colors and weight the result
- pi->value = evaluate_pawns<WHITE>(pos, wPawns, bPawns, pi)
- - evaluate_pawns<BLACK>(pos, bPawns, wPawns, pi);
+ Key key = pos.pawn_key();
+ Entry* e = entries[key];
- pi->value = apply_weight(pi->value, PawnStructureWeight);
+ if (e->key == key)
+ return e;
- return pi;
+ e->key = key;
+ e->value = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
+ return e;
}
-/// PawnInfoTable::evaluate_pawns() evaluates each pawn of the given color
+/// Entry::shelter_storm() calculates shelter and storm penalties for the file
+/// the king is on, as well as the two adjacent files.
template<Color Us>
-Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
- Bitboard theirPawns, PawnInfo* pi) {
+Value Entry::shelter_storm(const Position& pos, Square ksq) {
const Color Them = (Us == WHITE ? BLACK : WHITE);
+ static const Bitboard MiddleEdges = (FileABB | FileHBB) & (Rank2BB | Rank3BB);
- Bitboard b;
- Square s;
- File f;
- Rank r;
- bool passed, isolated, doubled, opposed, chain, backward, candidate;
- Score value = SCORE_ZERO;
- const Square* pl = pos.piece_list(Us, PAWN);
+ Value safety = MaxSafetyBonus;
+ Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, rank_of(ksq)) | rank_bb(ksq));
+ Bitboard ourPawns = b & pos.pieces(Us);
+ Bitboard theirPawns = b & pos.pieces(Them);
+ Rank rkUs, rkThem;
+ File kf = std::max(FILE_B, std::min(FILE_G, file_of(ksq)));
- // Loop through all pawns of the current color and score each pawn
- while ((s = *pl++) != SQ_NONE)
+ for (File f = kf - File(1); f <= kf + File(1); ++f)
{
- assert(pos.piece_on(s) == make_piece(Us, PAWN));
-
- f = file_of(s);
- r = rank_of(s);
-
- // This file cannot be half open
- pi->halfOpenFiles[Us] &= ~(1 << f);
-
- // Our rank plus previous one. Used for chain detection
- b = rank_bb(r) | rank_bb(Us == WHITE ? r - Rank(1) : r + Rank(1));
-
- // Flag the pawn as passed, isolated, doubled or member of a pawn
- // chain (but not the backward one).
- passed = !(theirPawns & passed_pawn_mask(Us, s));
- doubled = ourPawns & squares_in_front_of(Us, s);
- opposed = theirPawns & squares_in_front_of(Us, s);
- isolated = !(ourPawns & adjacent_files_bb(f));
- chain = ourPawns & adjacent_files_bb(f) & b;
-
- // Test for backward pawn
- backward = false;
-
- // If the pawn is passed, isolated, or member of a pawn chain it cannot
- // be backward. If there are friendly pawns behind on adjacent files
- // or if can capture an enemy pawn it cannot be backward either.
- if ( !(passed | isolated | chain)
- && !(ourPawns & attack_span_mask(Them, s))
- && !(pos.attacks_from<PAWN>(s, Us) & theirPawns))
- {
- // 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 seeing whether we meet a friendly or an enemy pawn first.
- b = pos.attacks_from<PAWN>(s, Us);
-
- // Note that we are sure to find something because pawn is not passed
- // nor isolated, so loop is potentially infinite, but it isn't.
- while (!(b & (ourPawns | theirPawns)))
- Us == WHITE ? b <<= 8 : b >>= 8;
-
- // The friendly pawn needs to be at least two ranks closer than the
- // enemy pawn in order to help the potentially backward pawn advance.
- backward = (b | (Us == WHITE ? b << 8 : b >> 8)) & theirPawns;
- }
-
- assert(opposed | passed | (attack_span_mask(Us, s) & theirPawns));
+ b = ourPawns & file_bb(f);
+ rkUs = b ? relative_rank(Us, backmost_sq(Us, b)) : RANK_1;
+
+ b = theirPawns & file_bb(f);
+ rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1;
+
+ if ( (MiddleEdges & make_square(f, rkThem))
+ && file_of(ksq) == f
+ && relative_rank(Us, ksq) == rkThem - 1)
+ safety += Value(200);
+ else
+ safety -= ShelterWeakness[rkUs]
+ + StormDanger[rkUs == RANK_1 ? 0 : rkThem == rkUs + 1 ? 2 : 1][rkThem];
+ }
- // 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 or equal than the number of
- // enemy pawns in the forward direction on the adjacent files.
- candidate = !(opposed | passed | backward | isolated)
- && (b = attack_span_mask(Them, s + pawn_push(Us)) & ourPawns) != 0
- && popcount<Max15>(b) >= popcount<Max15>(attack_span_mask(Us, s) & theirPawns);
+ return safety;
+}
- // 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 && !doubled)
- pi->passedPawns[Us] |= s;
- // Score this pawn
- if (isolated)
- value -= IsolatedPawnPenalty[opposed][f];
+/// Entry::update_safety() calculates and caches a bonus for king safety.
+/// It is called only when king square changes, which is about 20% of total
+/// king_safety() calls.
- if (doubled)
- value -= DoubledPawnPenalty[opposed][f];
+template<Color Us>
+Score Entry::update_safety(const Position& pos, Square ksq) {
- if (backward)
- value -= BackwardPawnPenalty[opposed][f];
+ kingSquares[Us] = ksq;
+ castlingRights[Us] = pos.can_castle(Us);
+ minKPdistance[Us] = 0;
- if (chain)
- value += ChainBonus[f];
+ Bitboard pawns = pos.pieces(Us, PAWN);
+ if (pawns)
+ while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
- if (candidate)
- value += CandidateBonus[relative_rank(Us, s)];
- }
- return value;
-}
+ if (relative_rank(Us, ksq) > RANK_4)
+ return kingSafety[Us] = make_score(0, -16 * minKPdistance[Us]);
-template<Color Us>
-int computePawnShelter(const Position &pos, Square ksq) {
- const Color Them = (Us == WHITE ? BLACK : WHITE);
- const File kingFile = ShelterFile[file_of(ksq)];
- const Bitboard ourPawns = pos.pieces(PAWN, Us) & in_front_bb(Us, ksq);
- const Bitboard theirPawns = pos.pieces(PAWN, Them) & (RankBB[rank_of(ksq)] | in_front_bb(Us, ksq));
-
- int shelter = 0;
-
- // Compute king shelter and storm values for the file the king is on, as well as the two adjacent files.
- for (int fileOffset = -1; fileOffset <= 1; fileOffset++) {
- // Shelter takes full penalty for center file, otherwise it's half penalty
- Bitboard shelterFile = ourPawns & FileBB[kingFile + fileOffset];
- Rank shelterClosest = shelterFile ? relative_rank<Us>(shelterFile)
- : RANK_1;
-
- shelter += fileOffset == 0 ? PawnShelter[shelterClosest]
- : score_non_center_file(PawnShelter[shelterClosest]);
-
- // Storm takes full penalty, unless there is an enemy pawn blocking us
- Bitboard stormFile = theirPawns & FileBB[kingFile + fileOffset];
- Rank stormClosest = stormFile ? relative_rank<Us>(stormFile)
- : RANK_1;
-
- shelter += shelterClosest + 1 == stormClosest ? PawnStorm[stormClosest] / 2
- : PawnStorm[stormClosest];
- }
-
- return shelter;
-}
+ Value bonus = shelter_storm<Us>(pos, ksq);
-/// PawnInfo::updateShelter() calculates and caches king shelter. It is called
-/// only when king square changes, about 20% of total king_shelter() calls.
-template<Color Us>
-Score PawnInfo::updateShelter(const Position& pos, Square ksq) {
- int shelter = 0;
+ // If we can castle use the bonus after the castling if it is bigger
+ if (pos.can_castle(MakeCastling<Us, KING_SIDE>::right))
+ bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
- if (relative_rank(Us, ksq) <= RANK_4)
- {
- shelter = computePawnShelter<Us>(pos, ksq);
- if (pos.can_castle(Us == WHITE ? WHITE_OO : BLACK_OO))
- shelter = std::min(shelter, computePawnShelter<Us>(pos, relative_square(Us, SQ_G1)));
- if (pos.can_castle(Us == WHITE ? WHITE_OOO : BLACK_OOO))
- shelter = std::min(shelter, computePawnShelter<Us>(pos, relative_square(Us, SQ_C1)));
- shelter = PawnShelterBasis - shelter;
- }
+ if (pos.can_castle(MakeCastling<Us, QUEEN_SIDE>::right))
+ bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
- kingSquares[Us] = ksq;
- kingShelters[Us] = make_score(shelter, 0);
- return kingShelters[Us];
+ return kingSafety[Us] = make_score(bonus, -16 * minKPdistance[Us]);
}
// Explicit template instantiation
-template Score PawnInfo::updateShelter<WHITE>(const Position& pos, Square ksq);
-template Score PawnInfo::updateShelter<BLACK>(const Position& pos, Square ksq);
+template Score Entry::update_safety<WHITE>(const Position& pos, Square ksq);
+template Score Entry::update_safety<BLACK>(const Position& pos, Square ksq);
+
+} // namespace Pawns
projects / stockfish / blobdiff