From: Gary Linscott <glinscott@gmail.com>
Date: Fri, 11 Apr 2014 15:04:48 +0000 (-0400)
Subject: Reduce penalty for doubled pawns further away from each other
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=45973245726d8ba62969891a15cf61fe46cc1f31;hp=ce6b7a1b859ab1b416e6df5bddfc942c9c2f9ae7

Reduce penalty for doubled pawns further away from each other

Passed both STC
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 38339 W: 6849 L: 6649 D: 24841

and LTC
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 22693 W: 3455 L: 3256 D: 15982

bench: 7508468
---

diff --git a/src/pawns.cpp b/src/pawns.cpp
index 1e625577..6d90f6b5 100644
--- a/src/pawns.cpp
+++ b/src/pawns.cpp
@@ -89,10 +89,10 @@ namespace {
     const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
     const Square Left  = (Us == WHITE ? DELTA_NW : DELTA_SE);
 
-    Bitboard b, p;
+    Bitboard b, p, doubled;
     Square s;
     File f;
-    bool passed, isolated, doubled, opposed, connected, backward, candidate, unsupported;
+    bool passed, isolated, opposed, connected, backward, candidate, unsupported;
     Score value = SCORE_ZERO;
     const Square* pl = pos.list<PAWN>(Us);
 
@@ -177,7 +177,7 @@ namespace {
             value -= UnsupportedPawnPenalty;
 
         if (doubled)
-            value -= Doubled[f];
+            value -= Doubled[f] / rank_distance(s, lsb(doubled));
 
         if (backward)
             value -= Backward[opposed][f];