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Move internal iterative reduction before probcut

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This patch moves IIR before probcut which allows probcut
to be produced at lower depths. Comments in IIR are also slightly updated.

Passed STC:
https://tests.stockfishchess.org/tests/view/6472d604d29264e4cfa749fd
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 387616 W: 103295 L: 102498 D: 181823
Ptnml(0-2): 976, 42322, 106381, 43187, 942

Passed LTC:
https://tests.stockfishchess.org/tests/view/6475eb8c4a36543c4c9f42e8
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 202836 W: 54901 L: 54281 D: 93654
Ptnml(0-2): 85, 19609, 61422, 20205, 97

closes https://github.com/official-stockfish/Stockfish/pull/4597

bench 2551691
This commit is contained in:
Michael Chaly 2023-06-01 15:24:13 +03:00 • committed by Joost VandeVondele
parent ced0311890
commit 8dea070538
1 changed files with 16 additions and 15 deletions
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31
src/search.cpp
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@ -822,9 +822,24 @@ namespace {
}
}
// Step 10. If the position doesn't a have ttMove, decrease depth by 2
// (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth).
// Use qsearch if depth is equal or below zero (~9 Elo)
if ( PvNode
&& !ttMove)
depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
if (depth <= 0)
return qsearch<PV>(pos, ss, alpha, beta);
if ( cutNode
&& depth >= 8
&& !ttMove)
depth -= 2;
probCutBeta = beta + 168 - 61 * improving;
// Step 10. ProbCut (~10 Elo)
// Step 11. ProbCut (~10 Elo)
// If we have a good enough capture (or queen promotion) and a reduced search returns a value
// much above beta, we can (almost) safely prune the previous move.
if ( !PvNode
@ -875,20 +890,6 @@ namespace {
Eval::NNUE::hint_common_parent_position(pos);
}
// Step 11. If the position is not in TT, decrease depth by 2 (or by 4 if the TT entry for the current position was hit and the stored depth is greater than or equal to the current depth).
// Use qsearch if depth is equal or below zero (~9 Elo)
if ( PvNode
&& !ttMove)
depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
if (depth <= 0)
return qsearch<PV>(pos, ss, alpha, beta);
if ( cutNode
&& depth >= 8
&& !ttMove)
depth -= 2;
moves_loop: // When in check, search starts here
// Step 12. A small Probcut idea, when we are in check (~4 Elo)