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Passed pawns evaluation tweak

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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>
This commit is contained in:
Marco Costalba 2009-05-25 15:48:47 +01:00
parent 3d0b60b065
commit 738bf66a2d
1 changed files with 16 additions and 22 deletions
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38
src/evaluate.cpp
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@ -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)