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Reintroduce depth reduction

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Reintroduce depth reduction if the position is not in TT.

STC https://tests.stockfishchess.org/tests/view/5f4652e85089a564a10d868c
LLR: 2.97 (-2.94,2.94) {-0.25,1.25}
Total: 40240 W: 4535 L: 4331 D: 31374
Ptnml(0-2): 215, 3276, 12969, 3410, 250

LTC https://tests.stockfishchess.org/tests/view/5f46ca5e5089a564a10d86f3
LLR: 2.93 (-2.94,2.94) {0.25,1.25}
Total: 63096 W: 3426 L: 3188 D: 56482
Ptnml(0-2): 51, 2798, 25645, 2970, 84

closes https://github.com/official-stockfish/Stockfish/pull/3072

bench: 3611906
This commit is contained in:
Unai Corzo 2020-08-28 09:27:15 +02:00 • committed by Joost VandeVondele
parent e4ed7d3dd7
commit d90d893b5e
1 changed files with 15 additions and 9 deletions
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24
src/search.cpp
View file

@ -940,6 +940,12 @@ namespace {
} }
} }
// Step 11. If the position is not in TT, decrease depth by 2
if ( PvNode
&& depth >= 6
&& !ttMove)
depth -= 2;
moves_loop: // When in check, search starts from here moves_loop: // When in check, search starts from here
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory, const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
@ -963,7 +969,7 @@ moves_loop: // When in check, search starts from here
// Mark this node as being searched // Mark this node as being searched
ThreadHolding th(thisThread, posKey, ss->ply); ThreadHolding th(thisThread, posKey, ss->ply);
// Step 11. Loop through all pseudo-legal moves until no moves remain // Step 12. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs. // or a beta cutoff occurs.
while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE) while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE)
{ {
@ -1001,7 +1007,7 @@ moves_loop: // When in check, search starts from here
// Calculate new depth for this move // Calculate new depth for this move
newDepth = depth - 1; newDepth = depth - 1;
// Step 12. Pruning at shallow depth (~200 Elo) // Step 13. Pruning at shallow depth (~200 Elo)
if ( !rootNode if ( !rootNode
&& pos.non_pawn_material(us) && pos.non_pawn_material(us)
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
@ -1059,7 +1065,7 @@ moves_loop: // When in check, search starts from here
} }
} }
// Step 13. Extensions (~75 Elo) // Step 14. Extensions (~75 Elo)
// Singular extension search (~70 Elo). If all moves but one fail low on a // Singular extension search (~70 Elo). If all moves but one fail low on a
// search of (alpha-s, beta-s), and just one fails high on (alpha, beta), // search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
@ -1142,10 +1148,10 @@ moves_loop: // When in check, search starts from here
[movedPiece] [movedPiece]
[to_sq(move)]; [to_sq(move)];
// Step 14. Make the move // Step 15. Make the move
pos.do_move(move, st, givesCheck); pos.do_move(move, st, givesCheck);
// Step 15. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be // Step 16. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be
// re-searched at full depth. // re-searched at full depth.
if ( depth >= 3 if ( depth >= 3
&& moveCount > 1 + 2 * rootNode + 2 * (PvNode && abs(bestValue) < 2) && moveCount > 1 + 2 * rootNode + 2 * (PvNode && abs(bestValue) < 2)
@ -1248,7 +1254,7 @@ moves_loop: // When in check, search starts from here
didLMR = false; didLMR = false;
} }
// Step 16. Full depth search when LMR is skipped or fails high // Step 17. Full depth search when LMR is skipped or fails high
if (doFullDepthSearch) if (doFullDepthSearch)
{ {
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
@ -1276,12 +1282,12 @@ moves_loop: // When in check, search starts from here
value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false); value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
} }
// Step 17. Undo move // Step 18. Undo move
pos.undo_move(move); pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE); assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
// Step 18. Check for a new best move // Step 19. Check for a new best move
// Finished searching the move. If a stop occurred, the return value of // Finished searching the move. If a stop occurred, the return value of
// the search cannot be trusted, and we return immediately without // the search cannot be trusted, and we return immediately without
// updating best move, PV and TT. // updating best move, PV and TT.
@ -1358,7 +1364,7 @@ moves_loop: // When in check, search starts from here
return VALUE_DRAW; return VALUE_DRAW;
*/ */
// Step 19. Check for mate and stalemate // Step 20. Check for mate and stalemate
// All legal moves have been searched and if there are no legal moves, it // All legal moves have been searched and if there are no legal moves, it
// must be a mate or a stalemate. If we are in a singular extension search then // must be a mate or a stalemate. If we are in a singular extension search then
// return a fail low score. // return a fail low score.