Improve the Chess960 correction for cornered bishops

vondele · snicolet · commit 329bdbd9cfa2 · 2021-10-06T11:57:34.000+02:00
As Chess960 patches can not be tested on fishtest, this was locally tuned and tested: Elo: 2.36 +- 1.07 LOS: 0.999992 closes #3730 Bench: 5714575
diff --git a/src/evaluate.cpp b/src/evaluate.cpp
@@ -1053,26 +1053,22 @@ namespace {
 
     if (   pos.piece_on(SQ_A1) == W_BISHOP
         && pos.piece_on(SQ_B2) == W_PAWN)
-        correction += !pos.empty(SQ_B3) ? -CorneredBishop * 4
-                                        : -CorneredBishop * 3;
+        correction -= CorneredBishop;
 
     if (   pos.piece_on(SQ_H1) == W_BISHOP
         && pos.piece_on(SQ_G2) == W_PAWN)
-        correction += !pos.empty(SQ_G3) ? -CorneredBishop * 4
-                                        : -CorneredBishop * 3;
+        correction -= CorneredBishop;
 
     if (   pos.piece_on(SQ_A8) == B_BISHOP
         && pos.piece_on(SQ_B7) == B_PAWN)
-        correction += !pos.empty(SQ_B6) ? CorneredBishop * 4
-                                        : CorneredBishop * 3;
+        correction += CorneredBishop;
 
     if (   pos.piece_on(SQ_H8) == B_BISHOP
         && pos.piece_on(SQ_G7) == B_PAWN)
-        correction += !pos.empty(SQ_G6) ? CorneredBishop * 4
-                                        : CorneredBishop * 3;
+        correction += CorneredBishop;
 
-    return pos.side_to_move() == WHITE ?  Value(correction)
-                                       : -Value(correction);
+    return pos.side_to_move() == WHITE ?  Value(5 * correction)
+                                       : -Value(5 * correction);
   }
 
 } // namespace Eval
