X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=src%2Fsearch.cpp;h=61c75d7dd9fc82d07598a4a328c7b59fdb1c2fb7;hb=913574f42123d16b0b473dcd8e373e95d3103633;hp=ed2b5743e6e2e353d36405b17f14922d095f52ce;hpb=5f8480a730cbc789d230dd28f276b8d35ce0a8a4;p=stockfish diff --git a/src/search.cpp b/src/search.cpp index ed2b5743..61c75d7d 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -67,7 +67,7 @@ namespace { return Value(140 * (d - improving)); } - // Reductions lookup table, initialized at startup + // Reductions lookup table initialized at startup int Reductions[MAX_MOVES]; // [depth or moveNumber] Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) { @@ -92,7 +92,7 @@ namespace { // Skill structure is used to implement strength limit. If we have an uci_elo then // we convert it to a suitable fractional skill level using anchoring to CCRL Elo - // (goldfish 1.13 = 2000) and a fit through Ordo derived Elo for match (TC 60+0.6) + // (goldfish 1.13 = 2000) and a fit through Ordo derived Elo for a match (TC 60+0.6) // results spanning a wide range of k values. struct Skill { Skill(int skill_level, int uci_elo) { @@ -304,7 +304,7 @@ void Thread::search() { Skill skill(Options["Skill Level"], Options["UCI_LimitStrength"] ? int(Options["UCI_Elo"]) : 0); // When playing with strength handicap enable MultiPV search that we will - // use behind the scenes to retrieve a set of possible moves. + // use behind-the-scenes to retrieve a set of possible moves. if (skill.enabled()) multiPV = std::max(multiPV, (size_t)4); @@ -321,7 +321,7 @@ void Thread::search() { if (mainThread) totBestMoveChanges /= 2; - // Save the last iteration's scores before first PV line is searched and + // Save the last iteration's scores before the first PV line is searched and // all the move scores except the (new) PV are set to -VALUE_INFINITE. for (RootMove& rm : rootMoves) rm.previousScore = rm.score; @@ -363,16 +363,16 @@ void Thread::search() { int failedHighCnt = 0; while (true) { - // Adjust the effective depth searched, but ensuring at least one effective increment for every + // Adjust the effective depth searched, but ensure at least one effective increment for every // four searchAgain steps (see issue #2717). Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - 3 * (searchAgainCounter + 1) / 4); bestValue = Stockfish::search(rootPos, ss, alpha, beta, adjustedDepth, false); // Bring the best move to the front. It is critical that sorting // is done with a stable algorithm because all the values but the - // first and eventually the new best one are set to -VALUE_INFINITE + // first and eventually the new best one is set to -VALUE_INFINITE // and we want to keep the same order for all the moves except the - // new PV that goes to the front. Note that in case of MultiPV + // new PV that goes to the front. Note that in the case of MultiPV // search the already searched PV lines are preserved. std::stable_sort(rootMoves.begin() + pvIdx, rootMoves.begin() + pvLast); @@ -440,7 +440,7 @@ void Thread::search() { if (!mainThread) continue; - // If skill level is enabled and time is up, pick a sub-optimal best move + // If the skill level is enabled and time is up, pick a sub-optimal best move if (skill.enabled() && skill.time_to_pick(rootDepth)) skill.pick_best(multiPV); @@ -498,7 +498,7 @@ void Thread::search() { mainThread->previousTimeReduction = timeReduction; - // If skill level is enabled, swap best PV line with the sub-optimal one + // If the skill level is enabled, swap the best PV line with the sub-optimal one if (skill.enabled()) std::swap(rootMoves[0], *std::find(rootMoves.begin(), rootMoves.end(), skill.best ? skill.best : skill.pick_best(multiPV))); @@ -515,7 +515,7 @@ namespace { constexpr bool PvNode = nodeType != NonPV; constexpr bool rootNode = nodeType == Root; - // Check if we have an upcoming move which draws by repetition, or + // Check if we have an upcoming move that draws by repetition, or // if the opponent had an alternative move earlier to this position. if ( !rootNode && pos.rule50_count() >= 3 @@ -548,7 +548,7 @@ namespace { bool givesCheck, improving, priorCapture, singularQuietLMR; bool capture, moveCountPruning, ttCapture; Piece movedPiece; - int moveCount, captureCount, quietCount, improvement; + int moveCount, captureCount, quietCount; // Step 1. Initialize node Thread* thisThread = pos.this_thread(); @@ -580,8 +580,8 @@ namespace { // would be at best mate_in(ss->ply+1), but if alpha is already bigger because // a shorter mate was found upward in the tree then there is no need to search // because we will never beat the current alpha. Same logic but with reversed - // signs applies also in the opposite condition of being mated instead of giving - // mate. In this case return a fail-high score. + // signs apply also in the opposite condition of being mated instead of giving + // mate. In this case, return a fail-high score. alpha = std::max(mated_in(ss->ply), alpha); beta = std::min(mate_in(ss->ply+1), beta); if (alpha >= beta) @@ -708,7 +708,6 @@ namespace { // Skip early pruning when in check ss->staticEval = eval = VALUE_NONE; improving = false; - improvement = 0; goto moves_loop; } else if (excludedMove) @@ -734,7 +733,7 @@ namespace { else { ss->staticEval = eval = evaluate(pos); - // Save static evaluation into transposition table + // Save static evaluation into the transposition table tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval); } @@ -745,14 +744,14 @@ namespace { thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus; } - // Set up the improvement variable, which is the difference between the current - // static evaluation and the previous static evaluation at our turn (if we were - // in check at our previous move we look at the move prior to it). The improvement - // margin and the improving flag are used in various pruning heuristics. - improvement = (ss-2)->staticEval != VALUE_NONE ? ss->staticEval - (ss-2)->staticEval - : (ss-4)->staticEval != VALUE_NONE ? ss->staticEval - (ss-4)->staticEval - : 173; - improving = improvement > 0; + // Set up the improving flag, which is true if current static evaluation is + // bigger than the previous static evaluation at our turn (if we were in + // check at our previous move we look at static evaluaion at move prior to it + // and if we were in check at move prior to it flag is set to true) and is + // false otherwise. The improving flag is used in various pruning heuristics. + improving = (ss-2)->staticEval != VALUE_NONE ? ss->staticEval > (ss-2)->staticEval + : (ss-4)->staticEval != VALUE_NONE ? ss->staticEval > (ss-4)->staticEval + : true; // Step 7. Razoring (~1 Elo). // If eval is really low check with qsearch if it can exceed alpha, if it can't, @@ -845,10 +844,10 @@ namespace { if ( !PvNode && depth > 3 && abs(beta) < VALUE_TB_WIN_IN_MAX_PLY - // if value from transposition table is lower than probCutBeta, don't attempt probCut + // If value from transposition table is lower than probCutBeta, don't attempt probCut // there and in further interactions with transposition table cutoff depth is set to depth - 3 // because probCut search has depth set to depth - 4 but we also do a move before it - // so effective depth is equal to depth - 3 + // So effective depth is equal to depth - 3 && !( tte->depth() >= depth - 3 && ttValue != VALUE_NONE && ttValue < probCutBeta)) @@ -920,7 +919,7 @@ moves_loop: // When in check, search starts here moveCountPruning = singularQuietLMR = false; // Indicate PvNodes that will probably fail low if the node was searched - // at a depth equal or greater than the current depth, and the result of this search was a fail low. + // at a depth equal to or greater than the current depth, and the result of this search was a fail low. bool likelyFailLow = PvNode && ttMove && (tte->bound() & BOUND_UPPER) @@ -936,8 +935,8 @@ moves_loop: // When in check, search starts here continue; // At root obey the "searchmoves" option and skip moves not listed in Root - // Move List. As a consequence any illegal move is also skipped. In MultiPV - // mode we also skip PV moves which have been already searched and those + // Move List. As a consequence, any illegal move is also skipped. In MultiPV + // mode we also skip PV moves that have been already searched and those // of lower "TB rank" if we are in a TB root position. if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->pvIdx, thisThread->rootMoves.begin() + thisThread->pvLast, move)) @@ -1005,7 +1004,7 @@ moves_loop: // When in check, search starts here { Square sq = pop_lsb(leftEnemies); attacks |= pos.attackers_to(sq, occupied) & pos.pieces(us) & occupied; - // don't consider pieces which were already threatened/hanging before SEE exchanges + // Don't consider pieces that were already threatened/hanging before SEE exchanges if (attacks && (sq != pos.square(~us) && (pos.attackers_to(sq, pos.pieces()) & pos.pieces(us)))) attacks = 0; } @@ -1090,7 +1089,7 @@ moves_loop: // When in check, search starts here // Our ttMove is assumed to fail high, and now we failed high also on a reduced // search without the ttMove. So we assume this expected Cut-node is not singular, // that multiple moves fail high, and we can prune the whole subtree by returning - // a soft bound. + // a softbound. else if (singularBeta >= beta) return singularBeta; @@ -1162,7 +1161,7 @@ moves_loop: // When in check, search starts here // Decrease reduction for PvNodes based on depth (~2 Elo) if (PvNode) - r -= 1 + 12 / (3 + depth); + r -= 1 + (depth < 6); // Decrease reduction if ttMove has been singularly extended (~1 Elo) if (singularQuietLMR) @@ -1186,7 +1185,7 @@ moves_loop: // When in check, search starts here // Step 17. Late moves reduction / extension (LMR, ~117 Elo) // We use various heuristics for the sons of a node after the first son has - // been searched. In general we would like to reduce them, but there are many + // been searched. In general, we would like to reduce them, but there are many // cases where we extend a son if it has good chances to be "interesting". if ( depth >= 2 && moveCount > 1 + (PvNode && ss->ply <= 1) @@ -1201,10 +1200,10 @@ moves_loop: // When in check, search starts here value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); - // Do full depth search when reduced LMR search fails high + // Do a full-depth search when reduced LMR search fails high if (value > alpha && d < newDepth) { - // Adjust full depth search based on LMR results - if result + // Adjust full-depth search based on LMR results - if the result // was good enough search deeper, if it was bad enough search shallower const bool doDeeperSearch = value > (bestValue + 64 + 11 * (newDepth - d)); const bool doEvenDeeperSearch = value > alpha + 711 && ss->doubleExtensions <= 6; @@ -1225,7 +1224,7 @@ moves_loop: // When in check, search starts here } } - // Step 18. Full depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1. + // Step 18. Full-depth search when LMR is skipped. If expected reduction is high, reduce its depth by 1. else if (!PvNode || moveCount > 1) { // Increase reduction for cut nodes and not ttMove (~1 Elo) @@ -1298,7 +1297,7 @@ moves_loop: // When in check, search starts here ++thisThread->bestMoveChanges; } else - // All other moves but the PV are set to the lowest value: this + // All other moves but the PV, are set to the lowest value: this // is not a problem when sorting because the sort is stable and the // move position in the list is preserved - just the PV is pushed up. rm.score = -VALUE_INFINITE; @@ -1337,7 +1336,7 @@ moves_loop: // When in check, search starts here } - // If the move is worse than some previously searched move, remember it to update its stats later + // If the move is worse than some previously searched move, remember it, to update its stats later if (move != bestMove) { if (capture && captureCount < 32) @@ -1349,7 +1348,7 @@ moves_loop: // When in check, search starts here } // The following condition would detect a stop only after move loop has been - // completed. But in this case bestValue is valid because we have fully + // completed. But in this case, bestValue is valid because we have fully // searched our subtree, and we can anyhow save the result in TT. /* if (Threads.stop) @@ -1368,7 +1367,7 @@ moves_loop: // When in check, search starts here ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW; - // If there is a move which produces search value greater than alpha we update stats of searched moves + // If there is a move that produces search value greater than alpha we update the stats of searched moves else if (bestMove) update_all_stats(pos, ss, bestMove, bestValue, beta, prevSq, quietsSearched, quietCount, capturesSearched, captureCount, depth); @@ -1703,28 +1702,28 @@ moves_loop: // When in check, search starts here Piece moved_piece = pos.moved_piece(bestMove); PieceType captured; - int bonus1 = stat_bonus(depth + 1); + int quietMoveBonus = stat_bonus(depth + 1); if (!pos.capture_stage(bestMove)) { - int bonus2 = bestValue > beta + 145 ? bonus1 // larger bonus - : stat_bonus(depth); // smaller bonus + int bestMoveBonus = bestValue > beta + 145 ? quietMoveBonus // larger bonus + : stat_bonus(depth); // smaller bonus // Increase stats for the best move in case it was a quiet move - update_quiet_stats(pos, ss, bestMove, bonus2); + update_quiet_stats(pos, ss, bestMove, bestMoveBonus); // Decrease stats for all non-best quiet moves for (int i = 0; i < quietCount; ++i) { - thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bonus2; - update_continuation_histories(ss, pos.moved_piece(quietsSearched[i]), to_sq(quietsSearched[i]), -bonus2); + thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bestMoveBonus; + update_continuation_histories(ss, pos.moved_piece(quietsSearched[i]), to_sq(quietsSearched[i]), -bestMoveBonus); } } else { // Increase stats for the best move in case it was a capture move captured = type_of(pos.piece_on(to_sq(bestMove))); - captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1; + captureHistory[moved_piece][to_sq(bestMove)][captured] << quietMoveBonus; } // Extra penalty for a quiet early move that was not a TT move or @@ -1732,14 +1731,14 @@ moves_loop: // When in check, search starts here if ( prevSq != SQ_NONE && ((ss-1)->moveCount == 1 + (ss-1)->ttHit || ((ss-1)->currentMove == (ss-1)->killers[0])) && !pos.captured_piece()) - update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -bonus1); + update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -quietMoveBonus); // Decrease stats for all non-best capture moves for (int i = 0; i < captureCount; ++i) { moved_piece = pos.moved_piece(capturesSearched[i]); captured = type_of(pos.piece_on(to_sq(capturesSearched[i]))); - captureHistory[moved_piece][to_sq(capturesSearched[i])][captured] << -bonus1; + captureHistory[moved_piece][to_sq(capturesSearched[i])][captured] << -quietMoveBonus; } } @@ -1751,7 +1750,7 @@ moves_loop: // When in check, search starts here for (int i : {1, 2, 4, 6}) { - // Only update first 2 continuation histories if we are in check + // Only update the first 2 continuation histories if we are in check if (ss->inCheck && i > 2) break; if (is_ok((ss-i)->currentMove)) @@ -1784,7 +1783,7 @@ moves_loop: // When in check, search starts here } } - // When playing with strength handicap, choose best move among a set of RootMoves + // When playing with strength handicap, choose the best move among a set of RootMoves // using a statistical rule dependent on 'level'. Idea by Heinz van Saanen. Move Skill::pick_best(size_t multiPV) { @@ -1915,7 +1914,7 @@ string UCI::pv(const Position& pos, Depth depth) { /// RootMove::extract_ponder_from_tt() is called in case we have no ponder move /// before exiting the search, for instance, in case we stop the search during a /// fail high at root. We try hard to have a ponder move to return to the GUI, -/// otherwise in case of 'ponder on' we have nothing to think on. +/// otherwise in case of 'ponder on' we have nothing to think about. bool RootMove::extract_ponder_from_tt(Position& pos) {