/*
Stockfish, a UCI chess playing engine derived from Glaurung 2.1
- Copyright (C) 2004-2021 The Stockfish developers (see AUTHORS file)
+ Copyright (C) 2004-2022 The Stockfish developers (see AUTHORS file)
Stockfish is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
// Reductions lookup table, initialized at startup
int Reductions[MAX_MOVES]; // [depth or moveNumber]
- Depth reduction(bool i, Depth d, int mn, bool rangeReduction) {
+ Depth reduction(bool i, Depth d, int mn, Value delta, Value rootDelta) {
int r = Reductions[d] * Reductions[mn];
- return (r + 534) / 1024 + (!i && r > 904) + rangeReduction;
+ return (r + 1358 - int(delta) * 1024 / int(rootDelta)) / 1024 + (!i && r > 904);
}
constexpr int futility_move_count(bool improving, Depth depth) {
if ( ss->ply > 10
&& search_explosion(thisThread) == MUST_CALM_DOWN
&& depth > (ss-1)->depth)
- depth = (ss-1)->depth;
+ depth = (ss-1)->depth;
constexpr bool PvNode = nodeType != NonPV;
constexpr bool rootNode = nodeType == Root;
&& (ttValue >= beta ? (tte->bound() & BOUND_LOWER)
: (tte->bound() & BOUND_UPPER)))
{
- // If ttMove is quiet, update move sorting heuristics on TT hit
+ // If ttMove is quiet, update move sorting heuristics on TT hit (~1 Elo)
if (ttMove)
{
if (ttValue >= beta)
{
- // Bonus for a quiet ttMove that fails high
+ // Bonus for a quiet ttMove that fails high (~3 Elo)
if (!ttCapture)
update_quiet_stats(pos, ss, ttMove, stat_bonus(depth));
- // Extra penalty for early quiet moves of the previous ply
+ // Extra penalty for early quiet moves of the previous ply (~0 Elo)
if ((ss-1)->moveCount <= 2 && !priorCapture)
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + 1));
}
- // Penalty for a quiet ttMove that fails low
+ // Penalty for a quiet ttMove that fails low (~1 Elo)
else if (!ttCapture)
{
int penalty = -stat_bonus(depth);
if (eval == VALUE_DRAW)
eval = value_draw(thisThread);
- // Can ttValue be used as a better position evaluation?
+ // ttValue can be used as a better position evaluation (~4 Elo)
if ( ttValue != VALUE_NONE
&& (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER)))
eval = ttValue;
tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
- // Use static evaluation difference to improve quiet move ordering
+ // Use static evaluation difference to improve quiet move ordering (~3 Elo)
if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture)
{
int bonus = std::clamp(-16 * int((ss-1)->staticEval + ss->staticEval), -2000, 2000);
improving = improvement > 0;
- // Step 7. Futility pruning: child node (~50 Elo).
+ // Step 7. Futility pruning: child node (~25 Elo).
// The depth condition is important for mate finding.
if ( !ss->ttPv
&& depth < 9
&& eval < 15000) // 50% larger than VALUE_KNOWN_WIN, but smaller than TB wins.
return eval;
- // Step 8. Null move search with verification search (~40 Elo)
+ // Step 8. Null move search with verification search (~22 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
&& (ss-1)->statScore < 23767
ss->ttPv = ttPv;
}
- // Step 10. If the position is not in TT, decrease depth by 2 or 1 depending on node type
+ // Step 10. If the position is not in TT, decrease depth by 2 or 1 depending on node type (~3 Elo)
if ( PvNode
&& depth >= 6
&& !ttMove)
moves_loop: // When in check, search starts here
- int rangeReduction = 0;
-
- // Step 11. A small Probcut idea, when we are in check
+ // Step 11. A small Probcut idea, when we are in check (~0 Elo)
probCutBeta = beta + 409;
if ( ss->inCheck
&& !PvNode
// Calculate new depth for this move
newDepth = depth - 1;
- // Step 13. Pruning at shallow depth (~200 Elo). Depth conditions are important for mate finding.
+ Value delta = beta - alpha;
+
+ // Step 13. Pruning at shallow depth (~98 Elo). Depth conditions are important for mate finding.
if ( !rootNode
&& pos.non_pawn_material(us)
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
{
- // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
+ // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~7 Elo)
moveCountPruning = moveCount >= futility_move_count(improving, depth);
// Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, rangeReduction > 2), 0);
+ int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, delta, thisThread->rootDelta), 0);
if ( captureOrPromotion
|| givesCheck)
{
- // Capture history based pruning when the move doesn't give check
- if ( !givesCheck
- && lmrDepth < 1
- && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] < 0)
+ // Futility pruning for captures (~0 Elo)
+ if ( !pos.empty(to_sq(move))
+ && !givesCheck
+ && !PvNode
+ && lmrDepth < 6
+ && !ss->inCheck
+ && ss->staticEval + 342 + 238 * lmrDepth + PieceValue[EG][pos.piece_on(to_sq(move))]
+ + captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 8 < alpha)
continue;
- // SEE based pruning
- if (!pos.see_ge(move, Value(-218) * depth)) // (~25 Elo)
+ // SEE based pruning (~9 Elo)
+ if (!pos.see_ge(move, Value(-218) * depth))
continue;
}
else
+ (*contHist[1])[movedPiece][to_sq(move)]
+ (*contHist[3])[movedPiece][to_sq(move)];
- // Continuation history based pruning (~20 Elo)
+ // Continuation history based pruning (~2 Elo)
if ( lmrDepth < 5
&& history < -3000 * depth + 3000)
continue;
history += thisThread->mainHistory[us][from_to(move)];
- lmrDepth = std::max(0, lmrDepth - (beta - alpha < thisThread->rootDelta / 4));
-
- // Futility pruning: parent node (~5 Elo)
+ // Futility pruning: parent node (~9 Elo)
if ( !ss->inCheck
&& lmrDepth < 8
&& ss->staticEval + 142 + 139 * lmrDepth + history / 64 <= alpha)
continue;
- // Prune moves with negative SEE (~20 Elo)
+ // Prune moves with negative SEE (~3 Elo)
if (!pos.see_ge(move, Value(-21 * lmrDepth * lmrDepth - 21 * lmrDepth)))
continue;
}
}
- // Step 14. Extensions (~75 Elo)
+ // Step 14. Extensions (~66 Elo)
- // Singular extension search (~70 Elo). If all moves but one fail low on a
+ // Singular extension search (~58 Elo). If all moves but one fail low on a
// search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
// then that move is singular and should be extended. To verify this we do
// a reduced search on all the other moves but the ttMove and if the
extension = -2;
}
- // Capture extensions for PvNodes and cutNodes
- else if ( (PvNode || cutNode)
- && captureOrPromotion
- && moveCount != 1)
- extension = 1;
-
- // Check extensions
+ // Check extensions (~1 Elo)
else if ( givesCheck
&& depth > 6
&& abs(ss->staticEval) > 100)
extension = 1;
- // Quiet ttMove extensions
+ // Quiet ttMove extensions (~0 Elo)
else if ( PvNode
&& move == ttMove
&& move == ss->killers[0]
bool doDeeperSearch = false;
- // Step 16. Late moves reduction / extension (LMR, ~200 Elo)
+ // Step 16. Late moves reduction / extension (LMR, ~98 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
// cases where we extend a son if it has good chances to be "interesting".
|| !captureOrPromotion
|| (cutNode && (ss-1)->moveCount > 1)))
{
- Depth r = reduction(improving, depth, moveCount, rangeReduction > 2);
+ Depth r = reduction(improving, depth, moveCount, delta, thisThread->rootDelta);
// Decrease reduction at some PvNodes (~2 Elo)
if ( PvNode
- && bestMoveCount <= 3
- && beta - alpha >= thisThread->rootDelta / 4)
+ && bestMoveCount <= 3)
r--;
// Decrease reduction if position is or has been on the PV
&& !likelyFailLow)
r -= 2;
- // Increase reduction at non-PV nodes (~3 Elo)
- if (!PvNode)
- r++;
-
// Decrease reduction if opponent's move count is high (~1 Elo)
if ((ss-1)->moveCount > 13)
r--;
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
- // Range reductions (~3 Elo)
- if (ss->staticEval - value < 30 && depth > 7)
- rangeReduction++;
-
// If the son is reduced and fails high it will be re-searched at full depth
doFullDepthSearch = value > alpha && d < newDepth;
- doDeeperSearch = value > alpha + 88;
+ doDeeperSearch = value > (alpha + 62 + 20 * (newDepth - d));
didLMR = true;
}
else
rm.pv.push_back(*m);
// We record how often the best move has been changed in each iteration.
- // This information is used for time management and LMR. In MultiPV mode,
+ // This information is used for time management. In MultiPV mode,
// we must take care to only do this for the first PV line.
if ( moveCount > 1
&& !thisThread->pvIdx)
if ((ss->staticEval = bestValue = tte->eval()) == VALUE_NONE)
ss->staticEval = bestValue = evaluate(pos);
- // Can ttValue be used as a better position evaluation?
+ // ttValue can be used as a better position evaluation (~7 Elo)
if ( ttValue != VALUE_NONE
&& (tte->bound() & (ttValue > bestValue ? BOUND_LOWER : BOUND_UPPER)))
bestValue = ttValue;
// to search the moves. Because the depth is <= 0 here, only captures,
// queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS)
// will be generated.
+ Square prevSq = to_sq((ss-1)->currentMove);
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
&thisThread->captureHistory,
contHist,
- to_sq((ss-1)->currentMove));
+ prevSq);
// Loop through the moves until no moves remain or a beta cutoff occurs
while ((move = mp.next_move()) != MOVE_NONE)
moveCount++;
- // Futility pruning and moveCount pruning
+ // Futility pruning and moveCount pruning (~5 Elo)
if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& !givesCheck
+ && to_sq(move) != prevSq
&& futilityBase > -VALUE_KNOWN_WIN
&& type_of(move) != PROMOTION)
{
}
}
- // Do not search moves with negative SEE values
+ // Do not search moves with negative SEE values (~5 Elo)
if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& !pos.see_ge(move))
continue;
[pos.moved_piece(move)]
[to_sq(move)];
- // Continuation history based pruning
+ // Continuation history based pruning (~2 Elo)
if ( !captureOrPromotion
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold
projects / stockfish / blobdiff