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Make LMR code easier to follow

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Remove flags doFullDepthSearch and didLMR, and reorder instruction.

Small measured speedup.

Closes https://github.com/official-stockfish/Stockfish/pull/4129

No functional change.
This commit is contained in:
mckx00 2022-08-13 05:32:30 -07:00 • committed by Joost VandeVondele
parent 4568f6369b
commit 3370f69881
1 changed files with 13 additions and 22 deletions
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35
src/search.cpp
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@ -558,8 +558,8 @@ namespace {
Move ttMove, move, excludedMove, bestMove;
Depth extension, newDepth;
Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
bool givesCheck, improving, didLMR, priorCapture, singularQuietLMR;
bool capture, doFullDepthSearch, moveCountPruning, ttCapture;
bool givesCheck, improving, priorCapture, singularQuietLMR;
bool capture, moveCountPruning, ttCapture;
Piece movedPiece;
int moveCount, captureCount, quietCount, improvement, complexity;
@ -1127,8 +1127,6 @@ moves_loop: // When in check, search starts here
// Step 16. Make the move
pos.do_move(move, st, givesCheck);
bool doDeeperSearch = false;
// Step 17. 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
@ -1187,25 +1185,12 @@ moves_loop: // When in check, search starts here
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
// If the son is reduced and fails high it will be re-searched at full depth
doFullDepthSearch = value > alpha && d < newDepth;
doDeeperSearch = value > (alpha + 78 + 11 * (newDepth - d));
didLMR = true;
}
else
{
doFullDepthSearch = !PvNode || moveCount > 1;
didLMR = false;
}
// Step 18. Full depth search when LMR is skipped or fails high
if (doFullDepthSearch)
{
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch, !cutNode);
// If the move passed LMR update its stats
if (didLMR)
// Do full depth search when reduced LMR search fails high
if (value > alpha && d < newDepth)
{
const bool doDeeperSearch = value > (alpha + 78 + 11 * (newDepth - d));
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth + doDeeperSearch, !cutNode);
int bonus = value > alpha ? stat_bonus(newDepth)
: -stat_bonus(newDepth);
@ -1216,6 +1201,12 @@ moves_loop: // When in check, search starts here
}
}
// Step 18. Full depth search when LMR is skipped
else if (!PvNode || moveCount > 1)
{
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
}
// For PV nodes only, do a full PV search on the first move or after a fail
// high (in the latter case search only if value < beta), otherwise let the
// parent node fail low with value <= alpha and try another move.