X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=763a6ac31194a8ae8b8a6e92bbbf0700894373a7;hp=9d091d02bc0cf5467bffac878ae4b5a893fc7621;hb=aedebe35cfa38b543041bae97e91e8194738b202;hpb=ed72a1e9ba37a9fa2674da8f46bb0597a1721c2d diff --git a/src/search.cpp b/src/search.cpp index 9d091d02..763a6ac3 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -2,6 +2,7 @@ Stockfish, a UCI chess playing engine derived from Glaurung 2.1 Copyright (C) 2004-2008 Tord Romstad (Glaurung author) Copyright (C) 2008-2015 Marco Costalba, Joona Kiiski, Tord Romstad + Copyright (C) 2015-2016 Marco Costalba, Joona Kiiski, Gary Linscott, 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 @@ -60,8 +61,8 @@ using namespace Search; namespace { - // Different node types, used as template parameter - enum NodeType { Root, PV, NonPV }; + // Different node types, used as a template parameter + enum NodeType { NonPV, PV }; // Razoring and futility margin based on depth const int razor_margin[4] = { 483, 570, 603, 554 }; @@ -75,7 +76,7 @@ namespace { return Reductions[PvNode][i][std::min(d, 63 * ONE_PLY)][std::min(mn, 63)]; } - // Skill struct is used to implement strength limiting + // Skill structure is used to implement strength limit struct Skill { Skill(int l) : level(l) {} bool enabled() const { return level < 20; } @@ -87,8 +88,8 @@ namespace { Move best = MOVE_NONE; }; - // EasyMoveManager struct is used to detect a so called 'easy move'; when PV is - // stable across multiple search iterations we can fast return the best move. + // EasyMoveManager structure is used to detect an 'easy move'. When the PV is + // stable across multiple search iterations, we can quickly return the best move. struct EasyMoveManager { void clear() { @@ -105,7 +106,7 @@ namespace { assert(newPv.size() >= 3); - // Keep track of how many times in a row 3rd ply remains stable + // Keep track of how many times in a row the 3rd ply remains stable stableCnt = (newPv[2] == pv[2]) ? stableCnt + 1 : 0; if (!std::equal(newPv.begin(), newPv.begin() + 3, pv)) @@ -127,10 +128,8 @@ namespace { }; EasyMoveManager EasyMove; - bool easyPlayed, failedLow; - double BestMoveChanges; Value DrawValue[COLOR_NB]; - CounterMovesHistoryStats CounterMovesHistory; + CounterMoveHistoryStats CounterMoveHistory; template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode); @@ -176,23 +175,25 @@ void Search::init() { } -/// Search::clear() resets to zero search state, to obtain reproducible results +/// Search::clear() resets search state to zero, to obtain reproducible results void Search::clear() { TT.clear(); - CounterMovesHistory.clear(); + CounterMoveHistory.clear(); for (Thread* th : Threads) { th->history.clear(); th->counterMoves.clear(); } + + Threads.main()->previousScore = VALUE_INFINITE; } /// Search::perft() is our utility to verify move generation. All the leaf nodes -/// up to the given depth are generated and counted and the sum returned. +/// up to the given depth are generated and counted, and the sum is returned. template uint64_t Search::perft(Position& pos, Depth depth) { @@ -222,8 +223,7 @@ template uint64_t Search::perft(Position&, Depth); /// MainThread::search() is called by the main thread when the program receives -/// the UCI 'go' command. It searches from root position and at the end prints -/// the "bestmove" to output. +/// the UCI 'go' command. It searches from the root position and outputs the "bestmove". void MainThread::search() { @@ -256,11 +256,12 @@ void MainThread::search() { } else { - if (TB::Cardinality >= rootPos.count(WHITE) - + rootPos.count(BLACK)) + if ( TB::Cardinality >= rootPos.count(WHITE) + + rootPos.count(BLACK) + && !rootPos.can_castle(ANY_CASTLING)) { - // If the current root position is in the tablebases then RootMoves - // contains only moves that preserve the draw or win. + // If the current root position is in the tablebases, then RootMoves + // contains only moves that preserve the draw or the win. TB::RootInTB = Tablebases::root_probe(rootPos, rootMoves, TB::Score); if (TB::RootInTB) @@ -268,7 +269,7 @@ void MainThread::search() { else // If DTZ tables are missing, use WDL tables as a fallback { - // Filter out moves that do not preserve a draw or win + // Filter out moves that do not preserve the draw or the win. TB::RootInTB = Tablebases::root_probe_wdl(rootPos, rootMoves, TB::Score); // Only probe during search if winning @@ -303,7 +304,7 @@ void MainThread::search() { } // When playing in 'nodes as time' mode, subtract the searched nodes from - // the available ones before to exit. + // the available ones before exiting. if (Limits.npmsec) Time.availableNodes += Limits.inc[us] - Threads.nodes_searched(); @@ -326,16 +327,21 @@ void MainThread::search() { if (th != this) th->wait_for_search_finished(); - // Check if there are threads with a better score than main thread. + // Check if there are threads with a better score than main thread Thread* bestThread = this; - if (!easyPlayed && Options["MultiPV"] == 1 && !Skill(Options["Skill Level"]).enabled()) + if ( !this->easyMovePlayed + && Options["MultiPV"] == 1 + && !Skill(Options["Skill Level"]).enabled()) + { for (Thread* th : Threads) if ( th->completedDepth > bestThread->completedDepth && th->rootMoves[0].score > bestThread->rootMoves[0].score) - bestThread = th; + bestThread = th; + } - // Send new PV when needed. - // FIXME: Breaks multiPV, and skill levels + previousScore = bestThread->rootMoves[0].score; + + // Send new PV when needed if (bestThread != this) sync_cout << UCI::pv(bestThread->rootPos, bestThread->completedDepth, -VALUE_INFINITE, VALUE_INFINITE) << sync_endl; @@ -347,17 +353,44 @@ void MainThread::search() { std::cout << sync_endl; } +const int halfDensityMap[][9] = +{ + {2, 0, 1}, + {2, 1, 0}, + + {4, 0, 0, 1, 1}, + {4, 0, 1, 1, 0}, + {4, 1, 1, 0, 0}, + {4, 1, 0, 0, 1}, + + {6, 0, 0, 0, 1, 1, 1}, + {6, 0, 0, 1, 1, 1, 0}, + {6, 0, 1, 1, 1, 0, 0}, + {6, 1, 1, 1, 0, 0, 0}, + {6, 1, 1, 0, 0, 0, 1}, + {6, 1, 0, 0, 0, 1, 1}, + + {8, 0, 0, 0, 0, 1, 1, 1, 1}, + {8, 0, 0, 0, 1, 1, 1, 1, 0}, + {8, 0, 0, 1, 1, 1, 1, 0 ,0}, + {8, 0, 1, 1, 1, 1, 0, 0 ,0}, + {8, 1, 1, 1, 1, 0, 0, 0 ,0}, + {8, 1, 1, 1, 0, 0, 0, 0 ,1}, + {8, 1, 1, 0, 0, 0, 0, 1 ,1}, + {8, 1, 0, 0, 0, 0, 1, 1 ,1}, +}; + // Thread::search() is the main iterative deepening loop. It calls search() // repeatedly with increasing depth until the allocated thinking time has been -// consumed, user stops the search, or the maximum search depth is reached. +// consumed, the user stops the search, or the maximum search depth is reached. void Thread::search() { Stack stack[MAX_PLY+4], *ss = stack+2; // To allow referencing (ss-2) and (ss+2) Value bestValue, alpha, beta, delta; Move easyMove = MOVE_NONE; - bool isMainThread = (this == Threads.main()); + MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr); std::memset(ss-2, 0, 5 * sizeof(Stack)); @@ -365,12 +398,12 @@ void Thread::search() { beta = VALUE_INFINITE; completedDepth = DEPTH_ZERO; - if (isMainThread) + if (mainThread) { easyMove = EasyMove.get(rootPos.key()); EasyMove.clear(); - easyPlayed = false; - BestMoveChanges = 0; + mainThread->easyMovePlayed = mainThread->failedLow = false; + mainThread->bestMoveChanges = 0; TT.new_search(); } @@ -384,36 +417,21 @@ void Thread::search() { multiPV = std::min(multiPV, rootMoves.size()); - // Iterative deepening loop until requested to stop or target depth reached + // Iterative deepening loop until requested to stop or the target depth is reached. while (++rootDepth < DEPTH_MAX && !Signals.stop && (!Limits.depth || rootDepth <= Limits.depth)) { - // Set up the new depth for the helper threads skipping in average each - // 2nd ply (using a half density map similar to a Hadamard matrix). - if (!isMainThread) + // Set up the new depths for the helper threads skipping on average every + // 2nd ply (using a half-density matrix). + if (!mainThread) { - int d = rootDepth + rootPos.game_ply(); - - if (idx <= 6 || idx > 24) - { - if (((d + idx) >> (msb(idx + 1) - 1)) % 2) - continue; - } - else - { - // Table of values of 6 bits with 3 of them set - static const int HalfDensityMap[] = { - 0x07, 0x0b, 0x0d, 0x0e, 0x13, 0x16, 0x19, 0x1a, 0x1c, - 0x23, 0x25, 0x26, 0x29, 0x2c, 0x31, 0x32, 0x34, 0x38 - }; - - if ((HalfDensityMap[idx - 7] >> (d % 6)) & 1) - continue; - } + int row = (idx - 1) % 20; + if (halfDensityMap[row][(rootDepth + rootPos.game_ply()) % halfDensityMap[row][0] + 1]) + continue; } // Age out PV variability metric - if (isMainThread) - BestMoveChanges *= 0.505, failedLow = false; + if (mainThread) + mainThread->bestMoveChanges *= 0.505, mainThread->failedLow = false; // Save the last iteration's scores before first PV line is searched and // all the move scores except the (new) PV are set to -VALUE_INFINITE. @@ -436,7 +454,7 @@ void Thread::search() { // high/low anymore. while (true) { - bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, false); + bestValue = ::search(rootPos, ss, alpha, beta, rootDepth, 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 @@ -446,20 +464,20 @@ void Thread::search() { // search the already searched PV lines are preserved. std::stable_sort(rootMoves.begin() + PVIdx, rootMoves.end()); - // Write PV back to transposition table in case the relevant + // Write PV back to the transposition table in case the relevant // entries have been overwritten during the search. for (size_t i = 0; i <= PVIdx; ++i) rootMoves[i].insert_pv_in_tt(rootPos); - // If search has been stopped break immediately. Sorting and + // If search has been stopped, break immediately. Sorting and // writing PV back to TT is safe because RootMoves is still - // valid, although it refers to previous iteration. + // valid, although it refers to the previous iteration. if (Signals.stop) break; // When failing high/low give some update (without cluttering // the UI) before a re-search. - if ( isMainThread + if ( mainThread && multiPV == 1 && (bestValue <= alpha || bestValue >= beta) && Time.elapsed() > 3000) @@ -472,9 +490,9 @@ void Thread::search() { beta = (alpha + beta) / 2; alpha = std::max(bestValue - delta, -VALUE_INFINITE); - if (isMainThread) + if (mainThread) { - failedLow = true; + mainThread->failedLow = true; Signals.stopOnPonderhit = false; } } @@ -494,7 +512,7 @@ void Thread::search() { // Sort the PV lines searched so far and update the GUI std::stable_sort(rootMoves.begin(), rootMoves.begin() + PVIdx + 1); - if (!isMainThread) + if (!mainThread) break; if (Signals.stop) @@ -508,7 +526,7 @@ void Thread::search() { if (!Signals.stop) completedDepth = rootDepth; - if (!isMainThread) + if (!mainThread) continue; // If skill level is enabled and time is up, pick a sub-optimal best move @@ -526,18 +544,22 @@ void Thread::search() { { if (!Signals.stop && !Signals.stopOnPonderhit) { - // Take some extra time if the best move has changed - if (rootDepth > 4 * ONE_PLY && multiPV == 1) - Time.pv_instability(BestMoveChanges); - - // Stop the search if only one legal move is available or all - // of the available time has been used or we matched an easyMove + // Stop the search if only one legal move is available, or if all + // of the available time has been used, or if we matched an easyMove // from the previous search and just did a fast verification. + const bool F[] = { !mainThread->failedLow, + bestValue >= mainThread->previousScore }; + + int improvingFactor = 640 - 160*F[0] - 126*F[1] - 124*F[0]*F[1]; + double unstablePvFactor = 1 + mainThread->bestMoveChanges; + + bool doEasyMove = rootMoves[0].pv[0] == easyMove + && mainThread->bestMoveChanges < 0.03 + && Time.elapsed() > Time.optimum() * 25 / 204; + if ( rootMoves.size() == 1 - || Time.elapsed() > Time.available() * (failedLow? 641 : 315)/640 - || ( easyPlayed = ( rootMoves[0].pv[0] == easyMove - && BestMoveChanges < 0.03 - && Time.elapsed() > Time.available() / 8))) + || Time.elapsed() > Time.optimum() * unstablePvFactor * improvingFactor / 634 + || (mainThread->easyMovePlayed = doEasyMove)) { // If we are allowed to ponder do not stop the search now but // keep pondering until the GUI sends "ponderhit" or "stop". @@ -555,12 +577,12 @@ void Thread::search() { } } - if (!isMainThread) + if (!mainThread) return; // Clear any candidate easy move that wasn't stable for the last search // iterations; the second condition prevents consecutive fast moves. - if (EasyMove.stableCnt < 6 || easyPlayed) + if (EasyMove.stableCnt < 6 || mainThread->easyMovePlayed) EasyMove.clear(); // If skill level is enabled, swap best PV line with the sub-optimal one @@ -577,8 +599,8 @@ namespace { template Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) { - const bool RootNode = NT == Root; - const bool PvNode = NT == PV || NT == Root; + const bool PvNode = NT == PV; + const bool rootNode = PvNode && (ss-1)->ply == 0; assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); @@ -602,7 +624,7 @@ namespace { bestValue = -VALUE_INFINITE; ss->ply = (ss-1)->ply + 1; - // Check for available remaining time + // Check for the available remaining time if (thisThread->resetCalls.load(std::memory_order_relaxed)) { thisThread->resetCalls = false; @@ -620,7 +642,7 @@ namespace { if (PvNode && thisThread->maxPly < ss->ply) thisThread->maxPly = ss->ply; - if (!RootNode) + if (!rootNode) { // Step 2. Check for aborted search and immediate draw if (Signals.stop.load(std::memory_order_relaxed) || pos.is_draw() || ss->ply >= MAX_PLY) @@ -642,7 +664,7 @@ namespace { assert(0 <= ss->ply && ss->ply < MAX_PLY); ss->currentMove = (ss+1)->excludedMove = bestMove = MOVE_NONE; - (ss+1)->skipEarlyPruning = false; (ss+1)->reduction = DEPTH_ZERO; + (ss+1)->skipEarlyPruning = false; (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE; // Step 4. Transposition table lookup. We don't want the score of a partial @@ -652,7 +674,7 @@ namespace { posKey = excludedMove ? pos.exclusion_key() : pos.key(); tte = TT.probe(posKey, ttHit); ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE; - ttMove = RootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0] + ttMove = rootNode ? thisThread->rootMoves[thisThread->PVIdx].pv[0] : ttHit ? tte->move() : MOVE_NONE; // At non-PV nodes we check for an early TT cutoff @@ -673,13 +695,14 @@ namespace { } // Step 4a. Tablebase probe - if (!RootNode && TB::Cardinality) + if (!rootNode && TB::Cardinality) { int piecesCnt = pos.count(WHITE) + pos.count(BLACK); if ( piecesCnt <= TB::Cardinality && (piecesCnt < TB::Cardinality || depth >= TB::ProbeDepth) - && pos.rule50_count() == 0) + && pos.rule50_count() == 0 + && !pos.can_castle(ANY_CASTLING)) { int found, v = Tablebases::probe_wdl(pos, &found); @@ -750,7 +773,7 @@ namespace { } // Step 7. Futility pruning: child node (skipped when in check) - if ( !RootNode + if ( !rootNode && depth < 7 * ONE_PLY && eval - futility_margin(depth) >= beta && eval < VALUE_KNOWN_WIN // Do not return unproven wins @@ -834,7 +857,7 @@ namespace { { Depth d = depth - 2 * ONE_PLY - (PvNode ? DEPTH_ZERO : depth / 4); ss->skipEarlyPruning = true; - search(pos, ss, alpha, beta, d, true); + search(pos, ss, alpha, beta, d, true); ss->skipEarlyPruning = false; tte = TT.probe(posKey, ttHit); @@ -845,7 +868,7 @@ moves_loop: // When in check search starts from here Square prevSq = to_sq((ss-1)->currentMove); Move cm = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq]; - const CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq]; + const CounterMoveStats& cmh = CounterMoveHistory[pos.piece_on(prevSq)][prevSq]; MovePicker mp(pos, ttMove, depth, thisThread->history, cmh, cm, ss); CheckInfo ci(pos); @@ -854,7 +877,7 @@ moves_loop: // When in check search starts from here || ss->staticEval == VALUE_NONE ||(ss-2)->staticEval == VALUE_NONE; - singularExtensionNode = !RootNode + singularExtensionNode = !rootNode && depth >= 8 * ONE_PLY && ttMove != MOVE_NONE /* && ttValue != VALUE_NONE Already implicit in the next condition */ @@ -875,13 +898,13 @@ moves_loop: // When in check search starts from here // 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. - if (RootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx, + if (rootNode && !std::count(thisThread->rootMoves.begin() + thisThread->PVIdx, thisThread->rootMoves.end(), move)) continue; ss->moveCount = ++moveCount; - if (RootNode && thisThread == Threads.main() && Time.elapsed() > 3000) + if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000) sync_cout << "info depth " << depth / ONE_PLY << " currmove " << UCI::move(move, pos.is_chess960()) << " currmovenumber " << moveCount + thisThread->PVIdx << sync_endl; @@ -925,7 +948,7 @@ moves_loop: // When in check search starts from here newDepth = depth - ONE_PLY + extension; // Step 13. Pruning at shallow depth - if ( !RootNode + if ( !rootNode && !captureOrPromotion && !inCheck && !givesCheck @@ -967,7 +990,7 @@ moves_loop: // When in check search starts from here prefetch(TT.first_entry(pos.key_after(move))); // Check for legality just before making the move - if (!RootNode && !pos.legal(move, ci.pinned)) + if (!rootNode && !pos.legal(move, ci.pinned)) { ss->moveCount = --moveCount; continue; @@ -984,37 +1007,39 @@ moves_loop: // When in check search starts from here && moveCount > 1 && !captureOrPromotion) { - ss->reduction = reduction(improving, depth, moveCount); + Depth r = reduction(improving, depth, moveCount); // Increase reduction for cut nodes and moves with a bad history if ( (!PvNode && cutNode) || ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] < VALUE_ZERO && cmh[pos.piece_on(to_sq(move))][to_sq(move)] <= VALUE_ZERO)) - ss->reduction += ONE_PLY; - - // Decrease reduction for moves with a good history - if ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO - && cmh[pos.piece_on(to_sq(move))][to_sq(move)] > VALUE_ZERO) - ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY); - - // Decrease reduction for moves that escape a capture - if ( ss->reduction + r += ONE_PLY; + + // Decrease/increase reduction for moves with a good/bad history + int rHist = ( thisThread->history[pos.piece_on(to_sq(move))][to_sq(move)] + + cmh[pos.piece_on(to_sq(move))][to_sq(move)]) / 14980; + r = std::max(DEPTH_ZERO, r - rHist * ONE_PLY); + + // Decrease reduction for moves that escape a capture. Filter out + // castling moves, because they are coded as "king captures rook" and + // hence break make_move(). Also use see() instead of see_sign(), + // because the destination square is empty. + if ( r && type_of(move) == NORMAL && type_of(pos.piece_on(to_sq(move))) != PAWN && pos.see(make_move(to_sq(move), from_sq(move))) < VALUE_ZERO) - ss->reduction = std::max(DEPTH_ZERO, ss->reduction - ONE_PLY); + r = std::max(DEPTH_ZERO, r - ONE_PLY); - Depth d = std::max(newDepth - ss->reduction, ONE_PLY); + Depth d = std::max(newDepth - r, ONE_PLY); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); - doFullDepthSearch = (value > alpha && ss->reduction != DEPTH_ZERO); - ss->reduction = DEPTH_ZERO; + doFullDepthSearch = (value > alpha && r != DEPTH_ZERO); } else doFullDepthSearch = !PvNode || moveCount > 1; - // Step 16. Full depth search, when LMR is skipped or fails high + // Step 16. Full depth search when LMR is skipped or fails high if (doFullDepthSearch) value = newDepth < ONE_PLY ? givesCheck ? -qsearch(pos, ss+1, -(alpha+1), -alpha, DEPTH_ZERO) @@ -1023,8 +1048,8 @@ moves_loop: // When in check search starts from here // For PV nodes only, do a full PV search on the first move or after a fail // high (in the latter case search only if value < beta), otherwise let the - // parent node fail low with value <= alpha and to try another move. - if (PvNode && (moveCount == 1 || (value > alpha && (RootNode || value < beta)))) + // parent node fail low with value <= alpha and try another move. + if (PvNode && (moveCount == 1 || (value > alpha && (rootNode || value < beta)))) { (ss+1)->pv = pv; (ss+1)->pv[0] = MOVE_NONE; @@ -1040,14 +1065,14 @@ moves_loop: // When in check search starts from here assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Step 18. Check for new best move + // Step 18. Check for a new best move // Finished searching the move. If a stop occurred, the return value of // the search cannot be trusted, and we return immediately without // updating best move, PV and TT. if (Signals.stop.load(std::memory_order_relaxed)) return VALUE_ZERO; - if (RootNode) + if (rootNode) { RootMove& rm = *std::find(thisThread->rootMoves.begin(), thisThread->rootMoves.end(), move); @@ -1067,7 +1092,7 @@ moves_loop: // When in check search starts from here // iteration. This information is used for time management: When // the best move changes frequently, we allocate some more time. if (moveCount > 1 && thisThread == Threads.main()) - ++BestMoveChanges; + ++static_cast(thisThread)->bestMoveChanges; } else // All other moves but the PV are set to the lowest value: this is @@ -1091,7 +1116,7 @@ moves_loop: // When in check search starts from here bestMove = move; - if (PvNode && !RootNode) // Update pv even in fail-high case + if (PvNode && !rootNode) // Update pv even in fail-high case update_pv(ss->pv, move, (ss+1)->pv); if (PvNode && value < beta) // Update alpha! Always alpha < beta @@ -1108,7 +1133,7 @@ moves_loop: // When in check search starts from here quietsSearched[quietCount++] = move; } - // Following condition would detect a stop only after move loop has been + // 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 // searched our subtree, and we can anyhow save the result in TT. /* @@ -1118,7 +1143,7 @@ moves_loop: // When in check search starts from here // Step 20. Check for mate and stalemate // All legal moves have been searched and if there are no legal moves, it - // must be mate or stalemate. If we are in a singular extension search then + // must be a mate or a stalemate. If we are in a singular extension search then // return a fail low score. if (!moveCount) bestValue = excludedMove ? alpha @@ -1138,7 +1163,7 @@ moves_loop: // When in check search starts from here { Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1); Square prevPrevSq = to_sq((ss - 2)->currentMove); - CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq]; + CounterMoveStats& prevCmh = CounterMoveHistory[pos.piece_on(prevPrevSq)][prevPrevSq]; prevCmh.update(pos.piece_on(prevSq), prevSq, bonus); } @@ -1162,7 +1187,6 @@ moves_loop: // When in check search starts from here const bool PvNode = NT == PV; - assert(NT == PV || NT == NonPV); assert(InCheck == !!pos.checkers()); assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE); assert(PvNode || (alpha == beta - 1)); @@ -1324,7 +1348,7 @@ moves_loop: // When in check search starts from here assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); - // Check for new best move + // Check for a new best move if (value > bestValue) { bestValue = value; @@ -1415,7 +1439,7 @@ moves_loop: // When in check search starts from here Value bonus = Value((depth / ONE_PLY) * (depth / ONE_PLY) + depth / ONE_PLY - 1); Square prevSq = to_sq((ss-1)->currentMove); - CounterMovesStats& cmh = CounterMovesHistory[pos.piece_on(prevSq)][prevSq]; + CounterMoveStats& cmh = CounterMoveHistory[pos.piece_on(prevSq)][prevSq]; Thread* thisThread = pos.this_thread(); thisThread->history.update(pos.moved_piece(move), to_sq(move), bonus); @@ -1441,7 +1465,7 @@ moves_loop: // When in check search starts from here && is_ok((ss-2)->currentMove)) { Square prevPrevSq = to_sq((ss-2)->currentMove); - CounterMovesStats& prevCmh = CounterMovesHistory[pos.piece_on(prevPrevSq)][prevPrevSq]; + CounterMoveStats& prevCmh = CounterMoveHistory[pos.piece_on(prevPrevSq)][prevPrevSq]; prevCmh.update(pos.piece_on(prevSq), prevSq, -bonus - 2 * (depth + 1) / ONE_PLY); } } @@ -1462,8 +1486,8 @@ moves_loop: // When in check search starts from here int maxScore = -VALUE_INFINITE; // Choose best move. For each move score we add two terms, both dependent on - // weakness. One deterministic and bigger for weaker levels, and one random, - // then we choose the move with the resulting highest score. + // weakness. One is deterministic and bigger for weaker levels, and one is + // random. Then we choose the move with the resulting highest score. for (size_t i = 0; i < multiPV; ++i) { // This is our magic formula @@ -1593,7 +1617,7 @@ void RootMove::insert_pv_in_tt(Position& pos) { /// 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 +/// 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.