mirror of
https://github.com/sockspls/badfish
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c0d3010438
Position is win also if strong side has a bishop
and a knight (plus other material, otherwise
KBNK would be triggered instead of KXK).
This fixes a subtle bug where a search on position
k7/8/8/8/8/P7/PB6/K7 b - - 6 1
Instead of returning a draw score, suddendly returns
a big score. This happens because at one point in
search we reach this position:
8/Pk6/8/8/8/4B3/P7/K7 w - - 3 8
Where white can promote. In case of rook promotion (and also in case of
queen promotion) the resutling position gets a huge static eval that is
above VALUE_KNOWN_WIN (from the point of view of white). So for rook
promotion it is
&& futilityBase > -VALUE_KNOWN_WIN
that prevents futility pruning in qsearch. (Removing this condition indeed
lets the problem occur). Raising the static eval for K+B+N+X v K to a value
higher than VALUE_KNOWN_WIN fixes this particular problem without having to
introduce an extra futility pruning condition in qsearch.
I just checked and it seems K+R v K, K+2B v K and even K+B+N v K already get
a huge static eval. Why not K+B+N+P v K?
I think this fix corrects an oversight. There is special code for KBNK, but
KBNXK is handled by KXK, so the test for sufficient material should also test
for B+N.
bench: 8678654
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|---|---|---|
| .. | ||
| benchmark.cpp | ||
| bitbase.cpp | ||
| bitboard.cpp | ||
| bitboard.h | ||
| bitcount.h | ||
| book.cpp | ||
| book.h | ||
| endgame.cpp | ||
| endgame.h | ||
| evaluate.cpp | ||
| evaluate.h | ||
| main.cpp | ||
| Makefile | ||
| material.cpp | ||
| material.h | ||
| misc.cpp | ||
| misc.h | ||
| movegen.cpp | ||
| movegen.h | ||
| movepick.cpp | ||
| movepick.h | ||
| notation.cpp | ||
| notation.h | ||
| pawns.cpp | ||
| pawns.h | ||
| platform.h | ||
| position.cpp | ||
| position.h | ||
| psqtab.h | ||
| rkiss.h | ||
| search.cpp | ||
| search.h | ||
| thread.cpp | ||
| thread.h | ||
| timeman.cpp | ||
| timeman.h | ||
| tt.cpp | ||
| tt.h | ||
| types.h | ||
| uci.cpp | ||
| ucioption.cpp | ||
| ucioption.h | ||