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Range reductions #3717

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Range reductions #3717

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cd51938
adding the reduction
OfekShochat Sep 23, 2021
19e18c6
adding the range
OfekShochat Sep 24, 2021
2e9ba2c
changing constant to two
OfekShochat Sep 24, 2021
9ac5185
Merge branch 'official-stockfish:master' into range-reduction
OfekShochat Sep 24, 2021
806e686
bench 5443950
OfekShochat Sep 24, 2021
96b34d3
adding to AUTHORS file
OfekShochat Sep 24, 2021
c988142
fixing comment and changing b's name
OfekShochat Sep 24, 2021
e962aa8
fixing unknown variable
OfekShochat Sep 24, 2021
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1 change: 1 addition & 0 deletions AUTHORS
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Original file line number Diff line number Diff line change
Expand Up @@ -193,6 +193,7 @@ Unai Corzo (unaiic)
Uri Blass (uriblass)
Vince Negri (cuddlestmonkey)
zz4032
Ofek Shochat (ghostway)


# Additionally, we acknowledge the authors and maintainers of fishtest,
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14 changes: 10 additions & 4 deletions src/search.cpp
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Expand Up @@ -69,9 +69,9 @@ namespace {
// Reductions lookup table, initialized at startup
int Reductions[MAX_MOVES]; // [depth or moveNumber]

Depth reduction(bool i, Depth d, int mn) {
Depth reduction(bool i, Depth d, int mn, bool rangeReduction) {
int r = Reductions[d] * Reductions[mn];
return (r + 534) / 1024 + (!i && r > 904);
return (r + 534) / 1024 + (!i && r > 904) + rangeReduction;
}

constexpr int futility_move_count(bool improving, Depth depth) {
Expand Down Expand Up @@ -955,6 +955,7 @@ namespace {

ttCapture = ttMove && pos.capture_or_promotion(ttMove);

int rangeReduction = 0;
// Step 11. A small Probcut idea, when we are in check
probCutBeta = beta + 409;
if ( ss->inCheck
Expand Down Expand Up @@ -1041,7 +1042,7 @@ namespace {
moveCountPruning = moveCount >= futility_move_count(improving, depth);

// Reduced depth of the next LMR search
int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount), 0);
int lmrDepth = std::max(newDepth - reduction(improving, depth, moveCount, rangeReduction > 2), 0);

if ( captureOrPromotion
|| givesCheck)
Expand Down Expand Up @@ -1176,7 +1177,7 @@ namespace {
|| !ss->ttPv)
&& (!PvNode || ss->ply > 1 || thisThread->id() % 4 != 3))
{
Depth r = reduction(improving, depth, moveCount);
Depth r = reduction(improving, depth, moveCount, rangeReduction > 2);

if (PvNode)
r--;
Expand Down Expand Up @@ -1236,6 +1237,11 @@ namespace {

value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);

// Range reductions (~3 Elo)
if (ss->staticEval - value < 30 && depth > 7) {
rangeReduction += 1;
}

// If the son is reduced and fails high it will be re-searched at full depth
doFullDepthSearch = value > alpha && d < newDepth;
didLMR = true;
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