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Remove skipQuiets with mate fix. (official-stockfish#2021)

This removes the skipQuiets variable, as was done in an earlier round by
@protonspring, but fixes an oversight which led to wrong mate
announcements. Quiets can only be pruned when there is no mate score, so
set moveCountPruning at the right spot.

tested as a fix at STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 66321 W: 14690 L: 14657 D: 36974
http://tests.stockfishchess.org/tests/view/5c74f3170ebc5925cffd4b3c

and as the full patch at LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 25903 W: 4341 L: 4228 D: 17334
http://tests.stockfishchess.org/tests/view/5c7540030ebc5925cffd506f

Bench: 3292342
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vondele authored and mcostalba committed Feb 27, 2019
1 parent 7c5f5fb commit 82ff04b992a53c757519a6ff61576ebd267c0cee
Showing with 7 additions and 9 deletions.
  1. +7 −9 src/search.cpp
@@ -569,7 +569,7 @@ namespace {
Depth extension, newDepth;
Value bestValue, value, ttValue, eval, maxValue, pureStaticEval;
bool ttHit, ttPv, inCheck, givesCheck, improving;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets, ttCapture;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, ttCapture;
Piece movedPiece;
int moveCount, captureCount, quietCount;

@@ -879,12 +879,12 @@ namespace {
ss->killers);
value = bestValue; // Workaround a bogus 'uninitialized' warning under gcc

skipQuiets = false;
moveCountPruning = false;
ttCapture = ttMove && pos.capture_or_promotion(ttMove);

// Step 12. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
while ((move = mp.next_move(skipQuiets)) != MOVE_NONE)
while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE)
{
assert(is_ok(move));

@@ -913,9 +913,6 @@ namespace {
movedPiece = pos.moved_piece(move);
givesCheck = gives_check(pos, move);

moveCountPruning = depth < 16 * ONE_PLY
&& moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];

// Step 13. Extensions (~70 Elo)

// Singular extension search (~60 Elo). If all moves but one fail low on a
@@ -966,16 +963,17 @@ namespace {
&& pos.non_pawn_material(us)
&& bestValue > VALUE_MATED_IN_MAX_PLY)
{
// Skip quiet moves if movecount exceeds our FutilityMoveCount threshold
moveCountPruning = depth < 16 * ONE_PLY
&& moveCount >= FutilityMoveCounts[improving][depth / ONE_PLY];

if ( !captureOrPromotion
&& !givesCheck
&& !pos.advanced_pawn_push(move))
{
// Move count based pruning (~30 Elo)
if (moveCountPruning)
{
skipQuiets = true;
continue;
}

// Reduced depth of the next LMR search
int lmrDepth = std::max(newDepth - reduction<PvNode>(improving, depth, moveCount), DEPTH_ZERO) / ONE_PLY;

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