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Guard tt depth edits from racy underflows

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Two recent patches, involving editing TTEs, introduced potential racy underflows. Guarding against these doesn't appear to gain elo but does improve sanity.

fixes https://github.com/official-stockfish/Stockfish/issues/6847

STC: https://tests.stockfishchess.org/tests/view/6a1c8c4b818cacc1db0ad158
LLR: 3.85 (-2.94,2.94) <-1.75,0.25>
Total: 125984 W: 32248 L: 32055 D: 61681
Ptnml(0-2): 292, 13678, 34866, 13857, 299

SMP STC: https://tests.stockfishchess.org/tests/view/6a1fb2ba818cacc1db0ad2e2
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 104272 W: 26524 L: 26385 D: 51363
Ptnml(0-2): 103, 11650, 28494, 11783, 106

closes https://github.com/official-stockfish/Stockfish/pull/6883

No functional change
This commit is contained in:
Dubslow
2026-06-06 10:08:26 +02:00
committed by Joost VandeVondele
parent 645b636dfa
commit db11ca42d5
1 changed files with 6 additions and 2 deletions
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src/tt.cpp
+6 -2
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@@ -119,7 +119,8 @@ void TTEntry::save(
{
auto v16 = value16;
if (std::abs(v16) < VALUE_INFINITE && is_decisive(v16))
depth8--;
depth8 = std::max(int(depth8) - 1,
0); // guard against racy underflows, default to "unoccupied"
}
}
@@ -141,7 +142,10 @@ void TTWriter::write(
entry->save(k, v, pv, b, d, m, ev, curr_generation);
}
void TTWriter::penalize(int penalty) { entry->depth8 -= penalty; }
void TTWriter::penalize(int penalty) {
// guard against racy underflows, default to "unoccupied"
entry->depth8 = std::max(int(entry->depth8) - penalty, 0);
}
// A TranspositionTable is an array of Cluster, of size clusterCount. Each cluster consists of ClusterSize number