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Skip quiet moves based on moveCount pruning threshold and history stats

If we can moveCountPrune and next quiet move has negative stats,
then go directly to the next move stage (Bad_Captures).

Reduction formula is tweaked to compensate for the decrease in move count that is used in LMR.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 6847 W: 1276 L: 1123 D: 4448

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 48687 W: 6503 L: 6226 D: 35958

Bench: 5919519

Closes #1036
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VoyagerOne authored and zamar committed Mar 18, 2017
1 parent c80d52c commit 352bd6f5aa348e15909f50266fc5bdc003df35bf
Showing with 12 additions and 7 deletions.
  1. +4 −2 src/movepick.cpp
  2. +1 −1 src/movepick.h
  3. +7 −4 src/search.cpp
@@ -175,7 +175,7 @@ void MovePicker::score<EVASIONS>() {
/// left. It picks the move with the biggest value from a list of generated moves
/// taking care not to return the ttMove if it has already been searched.
Move MovePicker::next_move() {
Move MovePicker::next_move(bool skipQuiets) {
Move move;
@@ -248,9 +248,11 @@ Move MovePicker::next_move() {
++stage;
case QUIET:
while (cur < endMoves)
while ( cur < endMoves
&& (!skipQuiets || cur->value >= VALUE_ZERO))
{
move = *cur++;
if ( move != ttMove
&& move != ss->killers[0]
&& move != ss->killers[1]
@@ -95,7 +95,7 @@ class MovePicker {
MovePicker(const Position&, Move, Depth, Square);
MovePicker(const Position&, Move, Depth, Search::Stack*);
Move next_move();
Move next_move(bool skipQuiets = false);
private:
template<GenType> void score();
@@ -163,7 +163,7 @@ void Search::init() {
for (int d = 1; d < 64; ++d)
for (int mc = 1; mc < 64; ++mc)
{
double r = log(d) * log(mc) / 2;
double r = log(d) * log(mc) / 1.95;
Reductions[NonPV][imp][d][mc] = int(std::round(r));
Reductions[PV][imp][d][mc] = std::max(Reductions[NonPV][imp][d][mc] - 1, 0);
@@ -542,7 +542,7 @@ namespace {
Depth extension, newDepth;
Value bestValue, value, ttValue, eval;
bool ttHit, inCheck, givesCheck, singularExtensionNode, improving;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning, skipQuiets;
Piece moved_piece;
int moveCount, quietCount;
@@ -829,10 +829,11 @@ namespace {
&& !excludedMove // Recursive singular search is not allowed
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY;
skipQuiets = false;
// Step 11. Loop through moves
// Loop through all pseudo-legal moves until no moves remain or a beta cutoff occurs
while ((move = mp.next_move()) != MOVE_NONE)
while ((move = mp.next_move(skipQuiets)) != MOVE_NONE)
{
assert(is_ok(move));
@@ -906,8 +907,10 @@ namespace {
&& (!pos.advanced_pawn_push(move) || pos.non_pawn_material() >= 5000))
{
// Move count based pruning
if (moveCountPruning)
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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