From 29b5842da8d5477c0aea924cfd364c9e619456a2 Mon Sep 17 00:00:00 2001 From: Alain SAVARD Date: Fri, 8 Apr 2016 19:05:36 +0100 Subject: [PATCH 1/1] Backward simplication On top of the usual conditions a) some opponent in front (but no lever) b) some neighbours (in front) (but no neighbour behind or same rank) c) < rank_5 to find out if a pawn is backward we look at the squares in front of this pawn to reach the same rank as the next neighbour. In current master, a pawn is backward if any of those squares is controlled by an enemy pawn on an adjacent file In this version, a pawn is ALSO backward if any of those squares is occupied by an enemy pawn. STC: http://tests.stockfishchess.org/tests/view/56fe7efd0ebc59301a3541f1 LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 19051 W: 3557 L: 3433 D: 12061 LTC: http://tests.stockfishchess.org/tests/view/56febc2d0ebc59301a354209 LLR: 2.95 (-2.94,2.94) [-3.00,1.00] Total: 40810 W: 5619 L: 5526 D: 29665 Bench: 7525245 Resolves #614 --- src/pawns.cpp | 60 ++++++++++++++++++++++----------------------------- 1 file changed, 26 insertions(+), 34 deletions(-) diff --git a/src/pawns.cpp b/src/pawns.cpp index 5bf0e82e..86745924 100644 --- a/src/pawns.cpp +++ b/src/pawns.cpp @@ -99,9 +99,9 @@ namespace { const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW); const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE); - Bitboard b, neighbours, doubled, supported, phalanx; + Bitboard b, neighbours, stoppers, doubled, supported, phalanx; Square s; - bool passed, isolated, opposed, backward, lever, connected; + bool opposed, lever, connected, backward; Score score = SCORE_ZERO; const Square* pl = pos.squares(Us); const Bitboard* pawnAttacksBB = StepAttacksBB[make_piece(Us, PAWN)]; @@ -127,55 +127,47 @@ namespace { e->pawnAttacksSpan[Us] |= pawn_attack_span(Us, s); // Flag the pawn - neighbours = ourPawns & adjacent_files_bb(f); - doubled = ourPawns & forward_bb(Us, s); - opposed = theirPawns & forward_bb(Us, s); - passed = !(theirPawns & passed_pawn_mask(Us, s)); - lever = theirPawns & pawnAttacksBB[s]; - phalanx = neighbours & rank_bb(s); - supported = neighbours & rank_bb(s - Up); - connected = supported | phalanx; - isolated = !neighbours; - - // Test for backward pawn. - // If the pawn is passed, isolated, lever or connected it cannot be - // backward. If there are friendly pawns behind on adjacent files - // or if it is sufficiently advanced, it cannot be backward either. - if ( (passed | isolated | lever | connected) - || (ourPawns & pawn_attack_span(Them, s)) - || (relative_rank(Us, s) >= RANK_5)) + opposed = theirPawns & forward_bb(Us, s); + stoppers = theirPawns & passed_pawn_mask(Us, s); + lever = theirPawns & pawnAttacksBB[s]; + doubled = ourPawns & forward_bb(Us, s); + neighbours = ourPawns & adjacent_files_bb(f); + phalanx = neighbours & rank_bb(s); + supported = neighbours & rank_bb(s - Up); + connected = supported | phalanx; + + // A pawn is backward when it is behind all pawns of the same color on the + // adjacent files and cannot be safely advanced. + if (!neighbours || lever || relative_rank(Us, s) >= RANK_5) backward = false; else { - // We now know 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(b)) & theirPawns; + // Find the backmost rank with neighbours or stoppers + b = rank_bb(backmost_sq(Us, neighbours | stoppers)); + + // The pawn is backward when it cannot safely progress to that rank: + // either there is a stopper in the way on this rank, or there is a + // stopper on adjacent file which controls the way to that rank. + backward = (b | shift_bb(b & adjacent_files_bb(f))) & stoppers; + + assert(!backward || !(pawn_attack_span(Them, s + Up) & neighbours)); } - assert(opposed | passed | (pawn_attack_span(Us, s) & theirPawns)); - // Passed pawns will be properly scored in evaluation because we need // full attack info to evaluate them. Only the frontmost passed // pawn on each file is considered a true passed pawn. - if (passed && !doubled) + if (!(stoppers | doubled)) e->passedPawns[Us] |= s; // Score this pawn - if (isolated) + if (!neighbours) score -= Isolated[opposed][f]; else if (backward) score -= Backward[opposed]; else if (!supported) - score -= Unsupported[more_than_one(neighbours & rank_bb(s + Up))]; + score -= Unsupported[more_than_one(neighbours & pawnAttacksBB[s])]; if (connected) score += Connected[opposed][!!phalanx][more_than_one(supported)][relative_rank(Us, s)]; -- 2.39.2