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Add a see() function that take only destination square

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In this case firstlocates the least valuable attacker, if any,
then proceed as usual.

This will be used by next patch.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba
2008-12-09 11:20:47 +01:00
parent 235df6a887
commit aaad48464b
4 changed files with 52 additions and 20 deletions
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61
src/position.cpp
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@@ -1582,10 +1582,16 @@ void Position::undo_null_move(const UndoInfo &u) {
/// Position::see() is a static exchange evaluator: It tries to estimate the
/// material gain or loss resulting from a move. There are two versions of
/// this function: One which takes a move as input, and one which takes a
/// 'from' and a 'to' square. The function does not yet understand promotions
/// or en passant captures.
/// material gain or loss resulting from a move. There are three versions of
/// this function: One which takes a destination square as input, one takes a
/// move, and one which takes a 'from' and a 'to' square. The function does
/// not yet understand promotions or en passant captures.
int Position::see(Square to) const {
assert(square_is_ok(to));
return see(SQ_NONE, to);
}
int Position::see(Move m) const {
@@ -1595,18 +1601,22 @@ int Position::see(Move m) const {
int Position::see(Square from, Square to) const {
// Approximate material values, with pawn = 1
// Material values
static const int seeValues[18] = {
0, 1, 3, 3, 5, 10, 100, 0, 0, 1, 3, 3, 5, 10, 100, 0, 0, 0
0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
0, PawnValueMidgame, KnightValueMidgame, BishopValueMidgame,
RookValueMidgame, QueenValueMidgame, QueenValueMidgame*10, 0,
0, 0
};
Bitboard attackers, occ, b;
assert(square_is_ok(from));
assert(square_is_ok(from) || from == SQ_NONE);
assert(square_is_ok(to));
// Initialize colors
Color us = color_of_piece_on(from);
Color us = (from != SQ_NONE ? color_of_piece_on(from) : opposite_color(color_of_piece_on(to)));
Color them = opposite_color(us);
// Initialize pieces
@@ -1616,15 +1626,34 @@ int Position::see(Square from, Square to) const {
// Find all attackers to the destination square, with the moving piece
// removed, but possibly an X-ray attacker added behind it.
occ = occupied_squares();
clear_bit(&occ, from);
attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
| (bishop_attacks_bb(to, occ) & bishops_and_queens())
| (piece_attacks<KNIGHT>(to) & knights())
| (piece_attacks<KING>(to) & kings())
| (pawn_attacks(WHITE, to) & pawns(BLACK))
| (pawn_attacks(BLACK, to) & pawns(WHITE));
while (true)
{
clear_bit(&occ, from);
attackers = (rook_attacks_bb(to, occ) & rooks_and_queens())
| (bishop_attacks_bb(to, occ) & bishops_and_queens())
| (piece_attacks<KNIGHT>(to) & knights())
| (piece_attacks<KING>(to) & kings())
| (pawn_attacks(WHITE, to) & pawns(BLACK))
| (pawn_attacks(BLACK, to) & pawns(WHITE));
// If the opponent has no attackers, we are finished
if (from != SQ_NONE)
break;
// If we don't have any attacker we are finished
if ((attackers & pieces_of_color(us)) == EmptyBoardBB)
return 0;
// Locate the least valuable attacker to the destination square
// and use it to initialize from square.
PieceType pt;
for (pt = PAWN; !(attackers & pieces_of_color_and_type(us, pt)); pt++)
assert(pt < KING);
from = first_1(attackers & pieces_of_color_and_type(us, pt));
piece = piece_on(from);
}
// If the opponent has no attackers we are finished
if ((attackers & pieces_of_color(them)) == EmptyBoardBB)
return seeValues[capture];