From 82d66f6b72c656a3efc4fd54b6eb489a8f74a945 Mon Sep 17 00:00:00 2001 From: 31m059 <37052095+31m059@users.noreply.github.com> Date: Thu, 11 Jul 2019 09:14:57 -0400 Subject: [PATCH] Exclude passed pawns from Attacked2Unsupported We recently added a bonus for double pawn attacks on unsupported enemy pawns, on June 27. However, it is possible that the unsupported pawn may become a passer by simply pushing forward out of the double attack. By rewarding double attacks, we may inadvertently reward the creation of enemy passers, by encouraging both of our would-be stoppers to attack the enemy pawn even if there is no opposing friendly pawn on the same file. Here, we revise this term to exclude passed pawns. In order to simplify the code with this change included, we non-functionally rewrite Attacked2Unsupported to be a penalty for enemy attacks on friendly pawns, rather than a bonus for our attacks on enemy pawns. This allows us to exclude passed pawns with a simple & ~e->passedPawns[Us], while passedPawns[Them] is not yet defined in this part of the code. This dramatically reduces the proportion of positions in which Attacked2Unsupported is applied, to about a third of the original. To compensate, maintaining the same average effect across our bench positions, we nearly triple Attacked2Unsupported from S(0, 20) to S(0, 56). Although this pawn formation is rare, it is worth more than half a pawn in the endgame! STC: (stopped automatically by fishtest after 250,000 games) LLR: -0.87 (-2.94,2.94) [0.50,4.50] Total: 250000 W: 56585 L: 55383 D: 138032 http://tests.stockfishchess.org/tests/view/5d25795e0ebc5925cf0cfb51 LTC: LLR: 2.96 (-2.94,2.94) [0.00,3.50] Total: 81038 W: 13965 L: 13558 D: 53515 http://tests.stockfishchess.org/tests/view/5d25f3920ebc5925cf0d10dd Closes https://github.com/official-stockfish/Stockfish/pull/2233 Bench: 3765158 --- src/evaluate.cpp | 2 +- src/pawns.cpp | 19 ++++++++++--------- 2 files changed, 11 insertions(+), 10 deletions(-) diff --git a/src/evaluate.cpp b/src/evaluate.cpp index c4e02e4e..a52cdf09 100644 --- a/src/evaluate.cpp +++ b/src/evaluate.cpp @@ -655,7 +655,7 @@ namespace { !(unsafeSquares & blockSq) ? 9 : 0 ; - // Assign a larger bonus if the block square is defended. + // Assign a larger bonus if the block square is defended if (defendedSquares & blockSq) k += 5; diff --git a/src/pawns.cpp b/src/pawns.cpp index 45c40471..0d3a57bf 100644 --- a/src/pawns.cpp +++ b/src/pawns.cpp @@ -35,8 +35,8 @@ namespace { constexpr Score Backward = S( 9, 24); constexpr Score Doubled = S(11, 56); constexpr Score Isolated = S( 5, 15); - constexpr Score WeakUnopposed = S( 13, 27); - constexpr Score Attacked2Unsupported = S( 0, 20); + constexpr Score WeakUnopposed = S(13, 27); + constexpr Score Attacked2Unsupported = S(0, 56); // Connected pawn bonus constexpr int Connected[RANK_NB] = { 0, 7, 8, 12, 29, 48, 86 }; @@ -84,11 +84,6 @@ namespace { e->kingSquares[Us] = SQ_NONE; e->pawnAttacks[Us] = pawn_attacks_bb(ourPawns); - // Unsupported enemy pawns attacked twice by us - score += Attacked2Unsupported * popcount( theirPawns - & pawn_double_attacks_bb(ourPawns) - & ~pawn_attacks_bb(theirPawns)); - // Loop through all pawns of the current color and score each pawn while ((s = *pl++) != SQ_NONE) { @@ -116,8 +111,8 @@ namespace { // Passed pawns will be properly scored in evaluation because we need // full attack info to evaluate them. Include also not passed pawns - // which could become passed after one or two pawn pushes when are - // not attacked more times than defended. + // which could become passed after one or two pawn pushes when they + // are not attacked more times than defended. if ( !(stoppers ^ lever) || (!(stoppers ^ leverPush) && popcount(phalanx) >= popcount(leverPush))) e->passedPawns[Us] |= s; @@ -149,6 +144,12 @@ namespace { score -= Doubled; } + // Unsupported friendly pawns attacked twice by the enemy + score -= Attacked2Unsupported * popcount( ourPawns + & pawn_double_attacks_bb(theirPawns) + & ~pawn_attacks_bb(ourPawns) + & ~e->passedPawns[Us]); + return score; } -- 2.39.2