From: Stéphane Nicolet Date: Mon, 23 Apr 2018 07:48:53 +0000 (+0200) Subject: Simplify the ShelterStrength[] array X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=c794c8c8016dfdc8360c9d5ab74dffa9d93d9277;ds=sidebyside Simplify the ShelterStrength[] array Remove the distinction between the king file and the two neighbours files in the ShelterStrength[] array. Instead we initialize the safety variable in the evaluate_shelter() function with a -10 penalty if our king is on a semi-open file (ie. if our king is on a file without a pawn protection). Also rename shelter_storm() to evaluate_shelter() while there. STC: LLR: 2.96 (-2.94,2.94) [-3.00,1.00] Total: 23153 W: 4795 L: 4677 D: 13681 http://tests.stockfishchess.org/tests/view/5adcb83d0ebc595ec7ff8aa7 LTC: LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 25728 W: 3934 L: 3821 D: 17973 http://tests.stockfishchess.org/tests/view/5adcdcb60ebc595ec7ff8adb See the commit history in PR#1559 for the proof that the committed version is equivalent to the version in the tests above: https://github.com/official-stockfish/Stockfish/pull/1559 Full credit to @protonspring for the renormalized values of the ShelterStrength[] array used for the simplification. Thanks! Bench: 4703935 --- diff --git a/src/pawns.cpp b/src/pawns.cpp index d2ef33e6..72556172 100644 --- a/src/pawns.cpp +++ b/src/pawns.cpp @@ -43,17 +43,13 @@ namespace { // Doubled pawn penalty constexpr Score Doubled = S(18, 38); - // Weakness of our pawn shelter in front of the king by [isKingFile][distance from edge][rank]. - // RANK_1 = 0 is used for files where we have no pawns or our pawn is behind our king. - constexpr Value ShelterWeakness[][int(FILE_NB) / 2][RANK_NB] = { - { { V( 98), V(20), V(11), V(42), V( 83), V( 84), V(101) }, // Not On King file - { V(103), V( 8), V(33), V(86), V( 87), V(105), V(113) }, - { V(100), V( 2), V(65), V(95), V( 59), V( 89), V(115) }, - { V( 72), V( 6), V(52), V(74), V( 83), V( 84), V(112) } }, - { { V(105), V(19), V( 3), V(27), V( 85), V( 93), V( 84) }, // On King file - { V(121), V( 7), V(33), V(95), V(112), V( 86), V( 72) }, - { V(121), V(26), V(65), V(90), V( 65), V( 76), V(117) }, - { V( 79), V( 0), V(45), V(65), V( 94), V( 92), V(105) } } + // Strength of pawn shelter for our king by [distance from edge][rank]. + // RANK_1 = 0 is used for files where we have no pawn, or pawn is behind our king. + Value ShelterStrength[int(FILE_NB) / 2][RANK_NB] = { + { V( -9), V(64), V(77), V( 44), V( 4), V( -1), V(-11) }, + { V(-15), V(83), V(51), V(-10), V( 1), V(-10), V(-28) }, + { V(-18), V(84), V(27), V(-12), V(21), V( -7), V(-36) }, + { V( 12), V(79), V(25), V( 19), V( 9), V( -6), V(-33) } }; // Danger of enemy pawns moving toward our king by [type][distance from edge][rank]. @@ -78,10 +74,6 @@ namespace { { V(21), V( 23), V( 116), V(41), V(15) } } }; - // 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. - constexpr Value MaxSafetyBonus = V(258); - #undef S #undef V @@ -230,21 +222,21 @@ Entry* probe(const Position& pos) { } -/// Entry::shelter_storm() calculates shelter and storm penalties for the file -/// the king is on, as well as the two closest files. +/// Entry::evaluate_shelter() calculates the shelter bonus and the storm +/// penalty for a king, looking at the king file and the two closest files. template -Value Entry::shelter_storm(const Position& pos, Square ksq) { +Value Entry::evaluate_shelter(const Position& pos, Square ksq) { + enum { BlockedByKing, Unopposed, BlockedByPawn, Unblocked }; constexpr Color Them = (Us == WHITE ? BLACK : WHITE); constexpr Direction Down = (Us == WHITE ? SOUTH : NORTH); - enum { BlockedByKing, Unopposed, BlockedByPawn, Unblocked }; - Bitboard b = pos.pieces(PAWN) & (forward_ranks_bb(Us, ksq) | rank_bb(ksq)); Bitboard ourPawns = b & pos.pieces(Us); Bitboard theirPawns = b & pos.pieces(Them); - Value safety = MaxSafetyBonus; + + Value safety = (ourPawns & file_bb(ksq)) ? Value(5) : Value(-5); File center = std::max(FILE_B, std::min(FILE_G, file_of(ksq))); for (File f = File(center - 1); f <= File(center + 1); ++f) @@ -256,8 +248,8 @@ Value Entry::shelter_storm(const Position& pos, Square ksq) { Rank rkThem = b ? relative_rank(Us, frontmost_sq(Them, b)) : RANK_1; int d = std::min(f, ~f); - safety -= ShelterWeakness[f == file_of(ksq)][d][rkUs] - + StormDanger + safety += ShelterStrength[d][rkUs] + - StormDanger [(shift(b) & ksq) ? BlockedByKing : rkUs == RANK_1 ? Unopposed : rkThem == (rkUs + 1) ? BlockedByPawn : Unblocked] @@ -282,14 +274,14 @@ Score Entry::do_king_safety(const Position& pos, Square ksq) { if (pawns) while (!(DistanceRingBB[ksq][minKingPawnDistance++] & pawns)) {} - Value bonus = shelter_storm(pos, ksq); + Value bonus = evaluate_shelter(pos, ksq); // If we can castle use the bonus after the castling if it is bigger if (pos.can_castle(MakeCastling::right)) - bonus = std::max(bonus, shelter_storm(pos, relative_square(Us, SQ_G1))); + bonus = std::max(bonus, evaluate_shelter(pos, relative_square(Us, SQ_G1))); if (pos.can_castle(MakeCastling::right)) - bonus = std::max(bonus, shelter_storm(pos, relative_square(Us, SQ_C1))); + bonus = std::max(bonus, evaluate_shelter(pos, relative_square(Us, SQ_C1))); return make_score(bonus, -16 * minKingPawnDistance); } diff --git a/src/pawns.h b/src/pawns.h index f36168c9..ec926a42 100644 --- a/src/pawns.h +++ b/src/pawns.h @@ -59,7 +59,7 @@ struct Entry { Score do_king_safety(const Position& pos, Square ksq); template - Value shelter_storm(const Position& pos, Square ksq); + Value evaluate_shelter(const Position& pos, Square ksq); Key key; Score scores[COLOR_NB];