From 3dfda1b28e14d1f3c2422fed5f203e305f58af28 Mon Sep 17 00:00:00 2001 From: Vizvezdenec Date: Tue, 6 Apr 2021 16:51:05 +0300 Subject: [PATCH] Replace distanceFromPv with a better logic This patch removes the recently introduced distanceFromPv logic, and replaces it with following logic: if reduction of moves with low movecount is really negative, we search them deeper than the first move. passed STC: LLR: 2.95 (-2.94,2.94) {-0.20,1.10} Total: 153008 W: 13913 L: 13579 D: 125516 Ptnml(0-2): 547, 10811, 53470, 11113, 563 https://tests.stockfishchess.org/tests/view/6069c9d02b2df919fd5f04d2 passed LTC: LLR: 2.94 (-2.94,2.94) {0.20,0.90} Total: 101920 W: 3964 L: 3699 D: 94257 Ptnml(0-2): 55, 3279, 44019, 3560, 47 https://tests.stockfishchess.org/tests/view/606a99fd2b2df919fd5f0532 Closes https://github.com/official-stockfish/Stockfish/pull/3421 Bench: 4191632 --- src/search.cpp | 11 ++++------- src/search.h | 1 - 2 files changed, 4 insertions(+), 8 deletions(-) diff --git a/src/search.cpp b/src/search.cpp index ff8764d8..f23db4c1 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -618,7 +618,6 @@ namespace { moveCount = captureCount = quietCount = ss->moveCount = 0; bestValue = -VALUE_INFINITE; maxValue = VALUE_INFINITE; - ss->distanceFromPv = (PvNode ? 0 : ss->distanceFromPv); // Check for the available remaining time if (thisThread == Threads.main()) @@ -1180,8 +1179,6 @@ moves_loop: // When in check, search starts from here // Step 15. Make the move pos.do_move(move, st, givesCheck); - (ss+1)->distanceFromPv = ss->distanceFromPv + moveCount - 1; - // Step 16. Late moves reduction / extension (LMR, ~200 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 @@ -1280,10 +1277,10 @@ moves_loop: // When in check, search starts from here r -= ss->statScore / 14790; } - // In general we want to cap the LMR depth search at newDepth. But for nodes - // close to the principal variation the cap is at (newDepth + 1), which will - // allow these nodes to be searched deeper than the pv (up to 4 plies deeper). - Depth d = std::clamp(newDepth - r, 1, newDepth + ((ss+1)->distanceFromPv <= 4)); + // In general we want to cap the LMR depth search at newDepth. But if + // reductions are really negative and movecount is low, we allow this move + // to be searched deeper than the first move. + Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && moveCount <= 5)); value = -search(pos, ss+1, -(alpha+1), -alpha, d, true); diff --git a/src/search.h b/src/search.h index 6f9fbd05..811b2e2a 100644 --- a/src/search.h +++ b/src/search.h @@ -49,7 +49,6 @@ struct Stack { Value staticEval; int statScore; int moveCount; - int distanceFromPv; bool inCheck; bool ttPv; bool ttHit; -- 2.39.2