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Increase king safety score in case of opposite castling
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@snicolet
snicolet committed Apr 20, 2017
1 parent 57a3334 commit fa55770
Showing 1 changed file with 8 additions and 3 deletions.
11 changes: 8 additions & 3 deletions src/evaluate.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -481,8 +481,8 @@ namespace {
}

// King tropism: firstly, find squares that opponent attacks in our king flank
File kf = file_of(ksq);
b = ei.attackedBy[Them][ALL_PIECES] & KingFlank[kf] & Camp;
Bitboard kingFlank = KingFlank[file_of(ksq)];
b = ei.attackedBy[Them][ALL_PIECES] & kingFlank & Camp;

assert(((Us == WHITE ? b << 4 : b >> 4) & b) == 0);
assert(popcount(Us == WHITE ? b << 4 : b >> 4) == popcount(b));
Expand All @@ -494,8 +494,13 @@ namespace {

score -= CloseEnemies * popcount(b);

// Increase king safety score in case of opposite castling
int d = distance<File>(ksq, pos.square<KING>(Them));
if (d)
score += make_score(mg_value(score) * d / 8, 0);

// Penalty when our king is on a pawnless flank
if (!(pos.pieces(PAWN) & KingFlank[kf]))
if (!(pos.pieces(PAWN) & kingFlank))
score -= PawnlessFlank;

if (DoTrace)
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2 comments on commit fa55770

@locutus2
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Some oddities in your patch:

  1. if the kings are on the same file full king safety is applied, but if one king step a square aside the king safety is only 1/8. that is a big discontinuity.
  2. the maximum possible distance could be 7. So you always reduce king safety expect for distance zero.
  3. you zero the endgame value from the king safety calculation in pawns.cpp

@locutus2
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Sorry, I have overseen the += operator.

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