From: Marco Costalba <mcostalba@gmail.com>
Date: Sun, 17 Jun 2012 08:18:18 +0000 (+0100)
Subject: Add min pawn-king distance to endgame evaluation
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=4f5680950a4e4c55da2877e1be91efd2be1c76ba;ds=inline

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 f71e2a39..73a9b904 100644
--- 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)
-      return kingSafety[Us] = SCORE_ZERO;
+      return kingSafety[Us] = make_score(0, -16 * minKPdistance[Us]);
 
   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)));
 
-  return kingSafety[Us] = make_score(bonus, 0);
+  return kingSafety[Us] = make_score(bonus, -16 * minKPdistance[Us]);
 }
 
 // Explicit template instantiation