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Remove SEE optimizations

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Don't seem to help, perhaps because we
return an approximate SEE score instead of the
real negative score so that we have some bad capture
or evasion sub-optimal ordering that compensates
the speed up.

Anyhow after 999 games at 1+0
Mod vs Orig +240 =514 -245 -2 ELO

So almost no harm to remove and make the code simpler.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba
2009-11-01 22:09:53 +01:00
parent 70b7404a63
commit 12461996a5
3 changed files with 7 additions and 33 deletions
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34
src/position.cpp
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@@ -1300,13 +1300,13 @@ void Position::undo_null_move() {
int Position::see(Square to) const {
assert(square_is_ok(to));
return see(SQ_NONE, to, false);
return see(SQ_NONE, to);
}
int Position::see(Move m) const {
assert(move_is_ok(m));
return see(move_from(m), move_to(m), false);
return see(move_from(m), move_to(m));
}
int Position::see_sign(Move m) const {
@@ -1322,10 +1322,10 @@ int Position::see_sign(Move m) const {
&& type_of_piece_on(from) != KING)
return 1;
return see(from, to, true);
return see(from, to);
}
int Position::see(Square from, Square to, bool shortcut) const {
int Position::see(Square from, Square to) const {
// Material values
static const int seeValues[18] = {
@@ -1337,7 +1337,6 @@ int Position::see(Square from, Square to, bool shortcut) const {
};
Bitboard attackers, stmAttackers, b;
int pieceDiff = 0;
assert(!shortcut || from != SQ_NONE);
assert(square_is_ok(from) || from == SQ_NONE);
@@ -1356,22 +1355,6 @@ int Position::see(Square from, Square to, bool shortcut) const {
if (type_of_piece(piece) == KING)
return seeValues[capture];
// If captured piece is defended by enemy pawns or knights then SEE is negative
// when captured piece value does not compensate the lost of capturing one.
if (shortcut)
{
pieceDiff = seeValues[piece] - seeValues[capture];
if ( pieceDiff > seeValues[PAWN]
&&(attacks_from<PAWN>(to, us) & pieces(PAWN, them)))
return -(pieceDiff - seeValues[PAWN] / 2);
if ( pieceDiff > seeValues[KNIGHT]
&& pieces(KNIGHT, them)
&&(pieces(KNIGHT, them) & attacks_from<KNIGHT>(to)))
return -(pieceDiff - seeValues[KNIGHT] / 2);
}
// Handle en passant moves
if (st->epSquare == to && type_of_piece_on(from) == PAWN)
{
@@ -1442,15 +1425,6 @@ int Position::see(Square from, Square to, bool shortcut) const {
for (pt = PAWN; !(stmAttackers & pieces(pt)); pt++)
assert(pt < KING);
// If captured piece is defended by an enemy piece then SEE is negative
// if captured piece value does not compensate the lost of capturing one.
if (pieceDiff > seeValues[pt])
{
assert(shortcut);
return -(pieceDiff - seeValues[pt] / 2);
} else
pieceDiff = 0; // Only first cycle
// Remove the attacker we just found from the 'attackers' bitboard,
// and scan for new X-ray attacks behind the attacker.
b = stmAttackers & pieces(pt);