Browse files

Passed pawns evaluation tweak

Do not penalize if in our adavncing pawn's path there are
non-pawns enemy pieces. Especially if they can be attacked
by us.

Patch is mine, but original idea and also fixing of a first, wrong,
version of the patch is from Eelco de Groot.

Tests with Joona framework seems to confirm patch is good

Results for patch 'disabled'   based on 5776 games: Win percentage:
41.309  (+- 0.526)  [+- 1.053]
Results for patch 'enabled'  based on 6400 games: Win percentage:
42.422  (+- 0.500)  [+- 1.000]

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
  • Loading branch information...
1 parent 3d0b60b commit 738bf66a2d04d27ce8c5481fef52dc3adc3cafe1 @mcostalba committed May 25, 2009
Showing with 16 additions and 22 deletions.
  1. +16 −22 src/evaluate.cpp
View
38 src/evaluate.cpp
@@ -933,29 +933,23 @@ namespace {
&& (squares_behind(us, s) & pos.rooks_and_queens(them)))
b3 = b2;
- if ((b2 & pos.pieces_of_color(them)) == EmptyBoardBB)
- {
- // There are no enemy pieces in the pawn's path! Are any of the
- // squares in the pawn's path attacked by the enemy?
- if (b3 == EmptyBoardBB)
- // No enemy attacks, huge bonus!
- ebonus += Value(tr * (b2 == b4 ? 17 : 15));
- else
- // OK, there are enemy attacks. Are those squares which are
- // attacked by the enemy also attacked by us? If yes, big bonus
- // (but smaller than when there are no enemy attacks), if no,
- // somewhat smaller bonus.
- ebonus += Value(tr * ((b3 & b4) == b3 ? 13 : 8));
- }
+ // Squares attacked or occupied by enemy pieces
+ b3 |= (b2 & pos.pieces_of_color(them));
+
+ // There are no enemy pawns in the pawn's path
+ assert((b2 & pos.pieces_of_color_and_type(them, PAWN)) == EmptyBoardBB);
+
+ // Are any of the squares in the pawn's path attacked or occupied by the enemy?
+ if (b3 == EmptyBoardBB)
+ // No enemy attacks or pieces, huge bonus!
+ ebonus += Value(tr * (b2 == b4 ? 17 : 15));
else
- {
- // There are some enemy pieces in the pawn's path. While this is
- // sad, we still assign a moderate bonus if all squares in the path
- // which are either occupied by or attacked by enemy pieces are
- // also attacked by us.
- if (((b3 | (b2 & pos.pieces_of_color(them))) & ~b4) == EmptyBoardBB)
- ebonus += Value(tr * 6);
- }
+ // OK, there are enemy attacks or pieces (but not pawns). Are those
+ // squares which are attacked by the enemy also attacked by us?
+ // If yes, big bonus (but smaller than when there are no enemy attacks),
+ // if no, somewhat smaller bonus.
+ ebonus += Value(tr * ((b3 & b4) == b3 ? 13 : 8));
+
// At last, add a small bonus when there are no *friendly* pieces
// in the pawn's path.
if ((b2 & pos.pieces_of_color(us)) == EmptyBoardBB)

0 comments on commit 738bf66

Please sign in to comment.