Add min pawn-king distance to endgame evaluation

At endgame time push the king near his pawns (actually
one of them).

Original idea is from Critter (although slightly different),
implementation is mine and is completely different from the
original, in particular it is different the algorithm to
compute the minimum distance from pawns.

After 19895 games at 15"+0.05
Mod vs Orig 3638 - 3248 - 13009 ELO +7

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

diff --git a/src/pawns.cpp b/src/pawns.cpp
index f71e2a3970f8cbd520e8567ec7d6729126b05eb8..73a9b904b347757fda1ba601344dfd69f913259b 100644 (file)
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -268,7 +268,7 @@ Score PawnEntry::update_safety(const Position& pos, Square ksq) {
       while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
 
   if (relative_rank(Us, ksq) > RANK_4)
       while (!(DistanceRingsBB[ksq][minKPdistance[Us]++] & pawns)) {}
 
   if (relative_rank(Us, ksq) > RANK_4)

-      return kingSafety[Us] = SCORE_ZERO;
+      return kingSafety[Us] = make_score(0, -16 * minKPdistance[Us]);

 
   Value bonus = shelter_storm<Us>(pos, ksq);
 
 
   Value bonus = shelter_storm<Us>(pos, ksq);
 


@@ -279,7 +279,7 @@ Score PawnEntry::update_safety(const Position& pos, Square ksq) {
   if (pos.can_castle(make_castle_right(Us, QUEEN_SIDE)))
       bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
 
   if (pos.can_castle(make_castle_right(Us, QUEEN_SIDE)))
       bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
 

-  return kingSafety[Us] = make_score(bonus, 0);
+  return kingSafety[Us] = make_score(bonus, -16 * minKPdistance[Us]);

 }
 
 // Explicit template instantiation
 }
 
 // Explicit template instantiation