From d90d893b5eeea020b2d59d1372f5aa0a20b45412 Mon Sep 17 00:00:00 2001 From: Unai Corzo Date: Fri, 28 Aug 2020 09:27:15 +0200 Subject: [PATCH] Reintroduce depth reduction 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 --- src/search.cpp | 24 +++++++++++++++--------- 1 file changed, 15 insertions(+), 9 deletions(-) diff --git a/src/search.cpp b/src/search.cpp index cae8a684..77447043 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -939,6 +939,12 @@ 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 @@ -963,7 +969,7 @@ moves_loop: // When in check, search starts from here // Mark this node as being searched 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. 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 newDepth = depth - 1; - // Step 12. Pruning at shallow depth (~200 Elo) + // Step 13. Pruning at shallow depth (~200 Elo) if ( !rootNode && pos.non_pawn_material(us) && 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 // 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] [to_sq(move)]; - // Step 14. Make the move + // Step 15. Make the move 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. if ( depth >= 3 && moveCount > 1 + 2 * rootNode + 2 * (PvNode && abs(bestValue) < 2) @@ -1248,7 +1254,7 @@ moves_loop: // When in check, search starts from here 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) { value = -search(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode); @@ -1276,12 +1282,12 @@ moves_loop: // When in check, search starts from here value = -search(pos, ss+1, -beta, -alpha, newDepth, false); } - // Step 17. Undo move + // Step 18. Undo move pos.undo_move(move); 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 // the search cannot be trusted, and we return immediately without // updating best move, PV and TT. @@ -1358,7 +1364,7 @@ moves_loop: // When in check, search starts from here 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 // must be a mate or a stalemate. If we are in a singular extension search then // return a fail low score. -- 2.39.2