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Add stealmate detection to evaluation

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Currently a stealmate position is misevaluated
in a negative/positive score, this leads qsearch(),
that does not detects stealmates too, to return the
wrong score and this yields to some kind of endgames
to be completely misevaluated.

With this patch is fully fixed follwing position

7k/6p1/6B1/5K1P/8/8/8/8 w - - 0 1

Also in SMP case.

Correct root cause analysys by Ronald de Man.

bench: 8678654
This commit is contained in:
Marco Costalba 2014-05-03 11:45:58 +02:00
parent dc87ec7258
commit 9e8bf82350
1 changed files with 6 additions and 0 deletions
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6
src/evaluate.cpp
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@ -787,6 +787,12 @@ namespace {
sf = ScaleFactor(50 * sf / SCALE_FACTOR_NORMAL);
}
// Stealmate detection
Color stm = pos.side_to_move();
if ( (ei.attackedBy[stm][ALL_PIECES] == ei.attackedBy[stm][KING])
&& (!(ei.attackedBy[stm][KING] & ~ei.attackedBy[~stm][ALL_PIECES])))
sf = SCALE_FACTOR_DRAW;
// Interpolate between a middlegame and a (scaled by 'sf') endgame score
Value v = mg_value(score) * int(ei.mi->game_phase())
+ eg_value(score) * int(PHASE_MIDGAME - ei.mi->game_phase()) * sf / SCALE_FACTOR_NORMAL;