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Fix integer overflow.

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scaledBonus can reach rather large values,
which lead to an int overflow as detected anematode using ubsan.
(see https://github.com/official-stockfish/Stockfish/issues/6505#issuecomment-3696988889)

It can be fixed by scaling nominator and denominator appropriately,
which doesn't change the bench, as long as there is no overflow.

First overflow/bench change happens at depth 26

closes https://github.com/official-stockfish/Stockfish/pull/6540

Bench: 2050811
This commit is contained in:
Joost VandeVondele
2026-01-15 22:13:26 +01:00
parent eb5a65aeb0
commit 0b9068d510
1 changed files with 2 additions and 2 deletions
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src/search.cpp
+2 -2
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@@ -1432,6 +1432,7 @@ moves_loop: // When in check, search starts here
bonusScale = std::max(bonusScale, 0); bonusScale = std::max(bonusScale, 0);
// scaledBonus ranges from 0 to roughly 2.3M, overflows happen for multipliers larger than 900
const int scaledBonus = std::min(141 * depth - 87, 1351) * bonusScale; const int scaledBonus = std::min(141 * depth - 87, 1351) * bonusScale;
update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq, update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq,
@@ -1440,8 +1441,7 @@ moves_loop: // When in check, search starts here
mainHistory[~us][((ss - 1)->currentMove).raw()] << scaledBonus * 243 / 32768; mainHistory[~us][((ss - 1)->currentMove).raw()] << scaledBonus * 243 / 32768;
if (type_of(pos.piece_on(prevSq)) != PAWN && ((ss - 1)->currentMove).type_of() != PROMOTION) if (type_of(pos.piece_on(prevSq)) != PAWN && ((ss - 1)->currentMove).type_of() != PROMOTION)
sharedHistory.pawn_entry(pos)[pos.piece_on(prevSq)][prevSq] sharedHistory.pawn_entry(pos)[pos.piece_on(prevSq)][prevSq] << scaledBonus * 290 / 8192;
<< scaledBonus * 1160 / 32768;
} }
// Bonus for prior capture countermove that caused the fail low // Bonus for prior capture countermove that caused the fail low