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Reintroduce the old "trapped bishop in the corner" evaluation term

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for Chess960 games.

After 1918 games at 30"
Mod - Orig: 1052-866 (+532,-346,=1040), Elo +33.8
This commit is contained in:
Tord Romstad 2011-01-03 22:32:57 +01:00
parent 83d8d54216
commit d5f2e32b5c
1 changed files with 27 additions and 0 deletions
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27
src/evaluate.cpp
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@ -168,6 +168,11 @@ namespace {
// right to castle.
const Value TrappedRookPenalty = Value(180);
// Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
// a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
// happen in Chess960 games.
const Score TrappedBishopA1H1Penalty = make_score(100, 100);
// The SpaceMask[Color] contains the area of the board which is considered
// by the space evaluation. In the middle game, each side is given a bonus
// based on how many squares inside this area are safe and available for
@ -556,6 +561,28 @@ namespace {
bonus += (Piece == ROOK ? RookOn7thBonus : QueenOn7thBonus);
}
// Special extra evaluation for bishops
if (Piece == BISHOP)
{
// An important Chess960 pattern: A cornered bishop blocked by
// a friendly pawn diagonally in front of it is a very serious
// problem, especially when that pawn is also blocked.
if (s == relative_square(Us, SQ_A1) || s == relative_square(Us, SQ_H1))
{
SquareDelta d = pawn_push(Us)
+ (square_file(s) == FILE_A ? DELTA_E : DELTA_W);
if (pos.piece_on(s + d) == piece_of_color_and_type(Us, PAWN))
{
if (!pos.square_is_empty(s + d + pawn_push(Us)))
bonus -= 2*TrappedBishopA1H1Penalty;
else if (pos.piece_on(s + 2*d) == piece_of_color_and_type(Us, PAWN))
bonus -= TrappedBishopA1H1Penalty;
else
bonus -= TrappedBishopA1H1Penalty / 2;
}
}
}
// Special extra evaluation for rooks
if (Piece == ROOK)
{