// Razor and futility margins
constexpr int RazorMargin = 661;
Value futility_margin(Depth d, bool improving) {
- return Value(198 * (d / ONE_PLY) - 178 * improving);
+ return Value(198 * (d - improving));
}
// Reductions lookup table, initialized at startup
int Reductions[MAX_MOVES]; // [depth or moveNumber]
Depth reduction(bool i, Depth d, int mn) {
- int r = Reductions[d / ONE_PLY] * Reductions[mn];
- return ((r + 520) / 1024 + (!i && r > 999)) * ONE_PLY;
+ int r = Reductions[d] * Reductions[mn];
+ return (r + 520) / 1024 + (!i && r > 999);
}
constexpr int futility_move_count(bool improving, int depth) {
}
// History and stats update bonus, based on depth
- int stat_bonus(Depth depth) {
- int d = depth / ONE_PLY;
+ int stat_bonus(Depth d) {
return d > 17 ? -8 : 22 * d * d + 151 * d - 140;
}
// Add a small random component to draw evaluations to avoid 3fold-blindness
- Value value_draw(Depth depth, Thread* thisThread) {
- return depth < 4 * ONE_PLY ? VALUE_DRAW
- : VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
+ Value value_draw(Thread* thisThread) {
+ return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
}
// Skill structure is used to implement strength limit
struct Skill {
explicit Skill(int l) : level(l) {}
bool enabled() const { return level < 20; }
- bool time_to_pick(Depth depth) const { return depth / ONE_PLY == 1 + level; }
+ bool time_to_pick(Depth depth) const { return depth == 1 + level; }
Move pick_best(size_t multiPV);
int level;
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
template <NodeType NT>
- Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = DEPTH_ZERO);
+ Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = 0);
Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply);
StateInfo st;
uint64_t cnt, nodes = 0;
- const bool leaf = (depth == 2 * ONE_PLY);
+ const bool leaf = (depth == 2);
for (const auto& m : MoveList<LEGAL>(pos))
{
- if (Root && depth <= ONE_PLY)
+ if (Root && depth <= 1)
cnt = 1, nodes++;
else
{
pos.do_move(m, st);
- cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - ONE_PLY);
+ cnt = leaf ? MoveList<LEGAL>(pos).size() : perft<false>(pos, depth - 1);
nodes += cnt;
pos.undo_move(m);
}
void Search::init() {
for (int i = 1; i < MAX_MOVES; ++i)
- Reductions[i] = int(23.4 * std::log(i));
+ Reductions[i] = int((23.4 + std::log(Threads.size()) / 2) * std::log(i));
}
if (Limits.perft)
{
- nodes = perft<true>(rootPos, Limits.perft * ONE_PLY);
+ nodes = perft<true>(rootPos, Limits.perft);
sync_cout << "\nNodes searched: " << nodes << "\n" << sync_endl;
return;
}
Move pv[MAX_PLY+1];
Value bestValue, alpha, beta, delta;
Move lastBestMove = MOVE_NONE;
- Depth lastBestMoveDepth = DEPTH_ZERO;
+ Depth lastBestMoveDepth = 0;
MainThread* mainThread = (this == Threads.main() ? Threads.main() : nullptr);
double timeReduction = 1, totBestMoveChanges = 0;
Color us = rootPos.side_to_move();
: -make_score(ct, ct / 2));
// Iterative deepening loop until requested to stop or the target depth is reached
- while ( (rootDepth += ONE_PLY) < DEPTH_MAX
+ while ( ++rootDepth < MAX_PLY
&& !Threads.stop
- && !(Limits.depth && mainThread && rootDepth / ONE_PLY > Limits.depth))
+ && !(Limits.depth && mainThread && rootDepth > Limits.depth))
{
// Age out PV variability metric
if (mainThread)
selDepth = 0;
// Reset aspiration window starting size
- if (rootDepth >= 4 * ONE_PLY)
+ if (rootDepth >= 4)
{
Value previousScore = rootMoves[pvIdx].previousScore;
delta = Value(23);
int failedHighCnt = 0;
while (true)
{
- Depth adjustedDepth = std::max(ONE_PLY, rootDepth - failedHighCnt * ONE_PLY);
+ Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt);
bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
// Bring the best move to the front. It is critical that sorting
++failedHighCnt;
}
else
+ {
+ ++rootMoves[pvIdx].bestMoveCount;
break;
+ }
delta += delta / 4 + 5;
fallingEval = clamp(fallingEval, 0.5, 1.5);
// If the bestMove is stable over several iterations, reduce time accordingly
- timeReduction = lastBestMoveDepth + 9 * ONE_PLY < completedDepth ? 1.97 : 0.98;
+ timeReduction = lastBestMoveDepth + 9 < completedDepth ? 1.97 : 0.98;
double reduction = (1.36 + mainThread->previousTimeReduction) / (2.29 * timeReduction);
// Use part of the gained time from a previous stable move for the current move
&& !rootNode
&& pos.has_game_cycle(ss->ply))
{
- alpha = value_draw(depth, pos.this_thread());
+ alpha = value_draw(pos.this_thread());
if (alpha >= beta)
return alpha;
}
// Dive into quiescence search when the depth reaches zero
- if (depth < ONE_PLY)
+ if (depth <= 0)
return qsearch<NT>(pos, ss, alpha, beta);
assert(-VALUE_INFINITE <= alpha && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
- assert(DEPTH_ZERO < depth && depth < DEPTH_MAX);
+ assert(0 < depth && depth < MAX_PLY);
assert(!(PvNode && cutNode));
- assert(depth / ONE_PLY * ONE_PLY == depth);
Move pv[MAX_PLY+1], capturesSearched[32], quietsSearched[64];
StateInfo st;
|| pos.is_draw(ss->ply)
|| ss->ply >= MAX_PLY)
return (ss->ply >= MAX_PLY && !inCheck) ? evaluate(pos)
- : value_draw(depth, pos.this_thread());
+ : value_draw(pos.this_thread());
// Step 3. Mate distance pruning. Even if we mate at the next move our score
// would be at best mate_in(ss->ply+1), but if alpha is already bigger because
// Extra penalty for early quiet moves of the previous ply
if ((ss-1)->moveCount <= 2 && !pos.captured_piece())
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + 1));
}
// Penalty for a quiet ttMove that fails low
else if (!pos.capture_or_promotion(ttMove))
|| (b == BOUND_LOWER ? value >= beta : value <= alpha))
{
tte->save(posKey, value_to_tt(value, ss->ply), ttPv, b,
- std::min(DEPTH_MAX - ONE_PLY, depth + 6 * ONE_PLY),
+ std::min(MAX_PLY - 1, depth + 6),
MOVE_NONE, VALUE_NONE);
return value;
if (eval == VALUE_NONE)
ss->staticEval = eval = evaluate(pos);
+ if (eval == VALUE_DRAW)
+ eval = value_draw(thisThread);
+
// Can ttValue be used as a better position evaluation?
if ( ttValue != VALUE_NONE
&& (tte->bound() & (ttValue > eval ? BOUND_LOWER : BOUND_UPPER)))
// Step 7. Razoring (~2 Elo)
if ( !rootNode // The required rootNode PV handling is not available in qsearch
- && depth < 2 * ONE_PLY
+ && depth < 2
&& eval <= alpha - RazorMargin)
return qsearch<NT>(pos, ss, alpha, beta);
// Step 8. Futility pruning: child node (~30 Elo)
if ( !PvNode
- && depth < 7 * ONE_PLY
+ && depth < 7
&& eval - futility_margin(depth, improving) >= beta
&& eval < VALUE_KNOWN_WIN) // Do not return unproven wins
return eval;
&& (ss-1)->currentMove != MOVE_NULL
&& (ss-1)->statScore < 22661
&& eval >= beta
- && ss->staticEval >= beta - 33 * depth / ONE_PLY + 299
+ && eval >= ss->staticEval
+ && ss->staticEval >= beta - 33 * depth + 299 - improving * 30
&& !excludedMove
&& pos.non_pawn_material(us)
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
assert(eval - beta >= 0);
// Null move dynamic reduction based on depth and value
- Depth R = ((835 + 70 * depth / ONE_PLY) / 256 + std::min(int(eval - beta) / 185, 3)) * ONE_PLY;
+ Depth R = (835 + 70 * depth) / 256 + std::min(int(eval - beta) / 185, 3);
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[NO_PIECE][0];
if (nullValue >= VALUE_MATE_IN_MAX_PLY)
nullValue = beta;
- if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 13 * ONE_PLY))
+ if (thisThread->nmpMinPly || (abs(beta) < VALUE_KNOWN_WIN && depth < 13))
return nullValue;
assert(!thisThread->nmpMinPly); // Recursive verification is not allowed
// Do verification search at high depths, with null move pruning disabled
// for us, until ply exceeds nmpMinPly.
- thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / (4 * ONE_PLY);
+ thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / 4;
thisThread->nmpColor = us;
Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
// If we have a good enough capture and a reduced search returns a value
// much above beta, we can (almost) safely prune the previous move.
if ( !PvNode
- && depth >= 5 * ONE_PLY
+ && depth >= 5
&& abs(beta) < VALUE_MATE_IN_MAX_PLY)
{
Value raisedBeta = std::min(beta + 191 - 46 * improving, VALUE_INFINITE);
ss->currentMove = move;
ss->continuationHistory = &thisThread->continuationHistory[pos.moved_piece(move)][to_sq(move)];
- assert(depth >= 5 * ONE_PLY);
+ assert(depth >= 5);
pos.do_move(move, st);
// If the qsearch held, perform the regular search
if (value >= raisedBeta)
- value = -search<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4 * ONE_PLY, !cutNode);
+ value = -search<NonPV>(pos, ss+1, -raisedBeta, -raisedBeta+1, depth - 4, !cutNode);
pos.undo_move(move);
}
// Step 11. Internal iterative deepening (~2 Elo)
- if (depth >= 7 * ONE_PLY && !ttMove)
+ if (depth >= 7 && !ttMove)
{
- search<NT>(pos, ss, alpha, beta, depth - 7 * ONE_PLY, cutNode);
+ search<NT>(pos, ss, alpha, beta, depth - 7, cutNode);
tte = TT.probe(posKey, ttHit);
ttValue = ttHit ? value_from_tt(tte->value(), ss->ply) : VALUE_NONE;
ss->moveCount = ++moveCount;
if (rootNode && thisThread == Threads.main() && Time.elapsed() > 3000)
- sync_cout << "info depth " << depth / ONE_PLY
+ sync_cout << "info depth " << depth
<< " currmove " << UCI::move(move, pos.is_chess960())
<< " currmovenumber " << moveCount + thisThread->pvIdx << sync_endl;
if (PvNode)
(ss+1)->pv = nullptr;
- extension = DEPTH_ZERO;
+ extension = 0;
captureOrPromotion = pos.capture_or_promotion(move);
movedPiece = pos.moved_piece(move);
givesCheck = pos.gives_check(move);
// 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
// result is lower than ttValue minus a margin then we will extend the ttMove.
- if ( depth >= 6 * ONE_PLY
+ if ( depth >= 6
&& move == ttMove
&& !rootNode
&& !excludedMove // Avoid recursive singular search
/* && ttValue != VALUE_NONE Already implicit in the next condition */
&& abs(ttValue) < VALUE_KNOWN_WIN
&& (tte->bound() & BOUND_LOWER)
- && tte->depth() >= depth - 3 * ONE_PLY
+ && tte->depth() >= depth - 3
&& pos.legal(move))
{
- Value singularBeta = ttValue - 2 * depth / ONE_PLY;
- Depth halfDepth = depth / (2 * ONE_PLY) * ONE_PLY; // ONE_PLY invariant
+ Value singularBeta = ttValue - 2 * depth;
+ Depth halfDepth = depth / 2;
ss->excludedMove = move;
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, halfDepth, cutNode);
ss->excludedMove = MOVE_NONE;
if (value < singularBeta)
{
- extension = ONE_PLY;
+ extension = 1;
singularLMR++;
- if (value < singularBeta - std::min(4 * depth / ONE_PLY, 36))
+ if (value < singularBeta - std::min(4 * depth, 36))
singularLMR++;
}
// Check extension (~2 Elo)
else if ( givesCheck
&& (pos.is_discovery_check_on_king(~us, move) || pos.see_ge(move)))
- extension = ONE_PLY;
-
- // Castling extension
- else if (type_of(move) == CASTLING)
- extension = ONE_PLY;
+ extension = 1;
// Shuffle extension
else if ( PvNode
&& pos.rule50_count() > 18
- && depth < 3 * ONE_PLY
+ && depth < 3
&& ++thisThread->shuffleExts < thisThread->nodes.load(std::memory_order_relaxed) / 4) // To avoid too many extensions
- extension = ONE_PLY;
+ extension = 1;
// Passed pawn extension
else if ( move == ss->killers[0]
&& pos.advanced_pawn_push(move)
&& pos.pawn_passed(us, to_sq(move)))
- extension = ONE_PLY;
+ extension = 1;
+
+ // Castling extension
+ if (type_of(move) == CASTLING)
+ extension = 1;
// Calculate new depth for this move
- newDepth = depth - ONE_PLY + extension;
+ newDepth = depth - 1 + extension;
// Step 14. Pruning at shallow depth (~170 Elo)
if ( !rootNode
&& bestValue > VALUE_MATED_IN_MAX_PLY)
{
// Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
- moveCountPruning = moveCount >= futility_move_count(improving, depth / ONE_PLY);
+ moveCountPruning = moveCount >= futility_move_count(improving, depth);
if ( !captureOrPromotion
&& !givesCheck
continue;
// Reduced depth of the next LMR search
- int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), DEPTH_ZERO);
- lmrDepth /= ONE_PLY;
+ int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
// Countermoves based pruning (~20 Elo)
if ( lmrDepth < 4 + ((ss-1)->statScore > 0 || (ss-1)->moveCount == 1)
if (!pos.see_ge(move, Value(-(31 - std::min(lmrDepth, 18)) * lmrDepth * lmrDepth)))
continue;
}
- else if ( (!givesCheck || !extension)
- && !pos.see_ge(move, Value(-199) * (depth / ONE_PLY))) // (~20 Elo)
+ else if ( !(givesCheck && extension)
+ && !pos.see_ge(move, Value(-199) * depth)) // (~20 Elo)
continue;
}
// Step 16. Reduced depth search (LMR). If the move fails high it will be
// re-searched at full depth.
- if ( depth >= 3 * ONE_PLY
- && moveCount > 1 + 3 * rootNode
+ if ( depth >= 3
+ && moveCount > 1 + 2 * rootNode
+ && (!rootNode || thisThread->best_move_count(move) == 0)
&& ( !captureOrPromotion
|| moveCountPruning
|| ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
// Reduction if other threads are searching this position.
if (th.marked())
- r += ONE_PLY;
+ r++;
// Decrease reduction if position is or has been on the PV
if (ttPv)
- r -= 2 * ONE_PLY;
+ r -= 2;
// Decrease reduction if opponent's move count is high (~10 Elo)
if ((ss-1)->moveCount > 15)
- r -= ONE_PLY;
+ r--;
- // Decrease reduction if move has been singularly extended
- r -= singularLMR * ONE_PLY;
+ // Decrease reduction if ttMove has been singularly extended
+ r -= singularLMR;
if (!captureOrPromotion)
{
// Increase reduction if ttMove is a capture (~0 Elo)
if (ttCapture)
- r += ONE_PLY;
+ r++;
// Increase reduction for cut nodes (~5 Elo)
if (cutNode)
- r += 2 * ONE_PLY;
+ r += 2;
// 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(). (~5 Elo)
else if ( type_of(move) == NORMAL
- && !pos.see_ge(make_move(to_sq(move), from_sq(move))))
- r -= 2 * ONE_PLY;
+ && !pos.see_ge(reverse_move(move)))
+ r -= 2;
ss->statScore = thisThread->mainHistory[us][from_to(move)]
+ (*contHist[0])[movedPiece][to_sq(move)]
// Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
if (ss->statScore >= -99 && (ss-1)->statScore < -116)
- r -= ONE_PLY;
+ r--;
else if ((ss-1)->statScore >= -117 && ss->statScore < -144)
- r += ONE_PLY;
+ r++;
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- r -= ss->statScore / 16384 * ONE_PLY;
+ r -= ss->statScore / 16384;
}
- Depth d = clamp(newDepth - r, ONE_PLY, newDepth);
+ Depth d = clamp(newDepth - r, 1, newDepth);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
// Quiet best move: update move sorting heuristics
if (!pos.capture_or_promotion(bestMove))
update_quiet_stats(pos, ss, bestMove, quietsSearched, quietCount,
- stat_bonus(depth + (bestValue > beta + PawnValueMg ? ONE_PLY : DEPTH_ZERO)));
+ stat_bonus(depth + (bestValue > beta + PawnValueMg)));
- update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + ONE_PLY));
+ update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + 1));
// Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
if ( ((ss-1)->moveCount == 1 || ((ss-1)->currentMove == (ss-1)->killers[0]))
&& !pos.captured_piece())
- update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+ update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + 1));
}
// Bonus for prior countermove that caused the fail low
- else if ( (depth >= 3 * ONE_PLY || PvNode)
+ else if ( (depth >= 3 || PvNode)
&& !pos.captured_piece())
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, stat_bonus(depth));
assert(alpha >= -VALUE_INFINITE && alpha < beta && beta <= VALUE_INFINITE);
assert(PvNode || (alpha == beta - 1));
- assert(depth <= DEPTH_ZERO);
- assert(depth / ONE_PLY * ONE_PLY == depth);
+ assert(depth <= 0);
Move pv[MAX_PLY+1];
StateInfo st;
// Detect non-capture evasions that are candidates to be pruned
evasionPrunable = inCheck
- && (depth != DEPTH_ZERO || moveCount > 2)
+ && (depth != 0 || moveCount > 2)
&& bestValue > VALUE_MATED_IN_MAX_PLY
&& !pos.capture(move);
// Make and search the move
pos.do_move(move, st, givesCheck);
- value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - ONE_PLY);
+ value = -qsearch<NT>(pos, ss+1, -beta, -alpha, depth - 1);
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
thisThread->mainHistory[us][from_to(move)] << bonus;
update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
+ if (type_of(pos.moved_piece(move)) != PAWN)
+ thisThread->mainHistory[us][from_to(reverse_move(move))] << -bonus;
+
if (is_ok((ss-1)->currentMove))
{
Square prevSq = to_sq((ss-1)->currentMove);
{
bool updated = (i <= pvIdx && rootMoves[i].score != -VALUE_INFINITE);
- if (depth == ONE_PLY && !updated)
+ if (depth == 1 && !updated)
continue;
- Depth d = updated ? depth : depth - ONE_PLY;
+ Depth d = updated ? depth : depth - 1;
Value v = updated ? rootMoves[i].score : rootMoves[i].previousScore;
bool tb = TB::RootInTB && abs(v) < VALUE_MATE - MAX_PLY;
ss << "\n";
ss << "info"
- << " depth " << d / ONE_PLY
+ << " depth " << d
<< " seldepth " << rootMoves[i].selDepth
<< " multipv " << i + 1
<< " score " << UCI::value(v);
RootInTB = false;
UseRule50 = bool(Options["Syzygy50MoveRule"]);
- ProbeDepth = int(Options["SyzygyProbeDepth"]) * ONE_PLY;
+ ProbeDepth = int(Options["SyzygyProbeDepth"]);
Cardinality = int(Options["SyzygyProbeLimit"]);
bool dtz_available = true;
if (Cardinality > MaxCardinality)
{
Cardinality = MaxCardinality;
- ProbeDepth = DEPTH_ZERO;
+ ProbeDepth = 0;
}
if (Cardinality >= popcount(pos.pieces()) && !pos.can_castle(ANY_CASTLING))