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Replace distanceFromPv with a better logic

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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
This commit is contained in:
Vizvezdenec 2021-04-06 16:51:05 +03:00 • committed by Stéphane Nicolet
parent f40913f7f6
commit 3dfda1b28e
2 changed files with 4 additions and 8 deletions
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11
src/search.cpp
View file

@ -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<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);

1
src/search.h
View file

@ -49,7 +49,6 @@ struct Stack {
Value staticEval;
int statScore;
int moveCount;
int distanceFromPv;
bool inCheck;
bool ttPv;
bool ttHit;