&& (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)
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
Value delta = beta - alpha;
- // Step 13. Pruning at shallow depth (~200 Elo). Depth conditions are important for mate finding.
+ // 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
if ( captureOrPromotion
|| givesCheck)
{
- // Futility pruning for captures
+ // 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))]
+ && 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)];
- // 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;
}
- // 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".
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;
moveCount++;
- // Futility pruning and moveCount pruning
+ // Futility pruning and moveCount pruning (~5 Elo)
if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& !givesCheck
&& futilityBase > -VALUE_KNOWN_WIN
}
}
- // 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