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Retire mate threat detection from evaluation

Browse source 
Remove a lot of complex, obscure and useless code.

After 999 games at 1+0
Mod vs Orig +162 =673 -164 -1 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2010-05-07 09:39:28 +02:00
parent 35e39a196d
commit e0e4bdc991
2 changed files with 18 additions and 76 deletions
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91
src/evaluate.cpp
View file

@ -214,12 +214,6 @@ namespace {
const int BishopCheckBonus = 1;
const int KnightCheckBonus = 1;
// Scan for queen contact mates?
const bool QueenContactMates = true;
// Bonus for having a mate threat
const int MateThreatBonus = 3;
// InitKingDanger[] contains bonuses based on the position of the defending
// king.
const int InitKingDanger[64] = {
@ -418,11 +412,7 @@ Value do_evaluate(const Position& pos, EvalInfo& ei, int threadID) {
}
// Interpolate between the middle game and the endgame score
Color stm = pos.side_to_move();
Value v = Sign[stm] * scale_by_game_phase(ei.value, phase, factor);
return (ei.mateThreat[stm] == MOVE_NONE ? v : 8 * QueenValueMidgame - v);
return Sign[pos.side_to_move()] * scale_by_game_phase(ei.value, phase, factor);
}
} // namespace
@ -695,8 +685,7 @@ namespace {
const Color Them = (Us == WHITE ? BLACK : WHITE);
Bitboard undefended, attackedByOthers, escapeSquares, occ, b, b1, b2, safe;
Square from, to;
Bitboard undefended, b, b1, b2, safe;
bool sente;
int attackUnits, shelter = 0;
const Square ksq = pos.king_square(Us);
@ -711,8 +700,8 @@ namespace {
// King safety. This is quite complicated, and is almost certainly far
// from optimally tuned.
if ( pos.piece_count(Them, QUEEN) >= 1
&& ei.kingAttackersCount[Them] >= 2
&& pos.non_pawn_material(Them) >= QueenValueMidgame + RookValueMidgame
&& ei.kingAttackersCount[Them] >= 2
&& pos.non_pawn_material(Them) >= QueenValueMidgame + RookValueMidgame
&& ei.kingAdjacentZoneAttacksCount[Them])
{
// Is it the attackers turn to move?
@ -735,60 +724,29 @@ namespace {
+ InitKingDanger[relative_square(Us, ksq)]
- shelter / 32;
// Analyse safe queen contact checks
// Analyse enemy's safe queen contact checks. First find undefended
// squares around the king attacked by enemy queen...
b = undefended & ei.attacked_by(Them, QUEEN) & ~pos.pieces_of_color(Them);
if (b)
{
attackedByOthers = ei.attacked_by(Them, PAWN) | ei.attacked_by(Them, KNIGHT)
| ei.attacked_by(Them, BISHOP) | ei.attacked_by(Them, ROOK);
b &= attackedByOthers;
// Squares attacked by the queen and supported by another enemy piece and
// not defended by other pieces but our king.
// ...then remove squares not supported by another enemy piece
b &= ( ei.attacked_by(Them, PAWN) | ei.attacked_by(Them, KNIGHT)
| ei.attacked_by(Them, BISHOP) | ei.attacked_by(Them, ROOK));
if (b)
{
// The bitboard b now contains the squares available for safe queen
// contact checks.
attackUnits += QueenContactCheckBonus * count_1s_max_15<HasPopCnt>(b) * (sente ? 2 : 1);
// Is there a mate threat?
if (QueenContactMates && !pos.is_check())
{
escapeSquares = pos.attacks_from<KING>(ksq) & ~pos.pieces_of_color(Us) & ~attackedByOthers;
occ = pos.occupied_squares();
while (b)
{
to = pop_1st_bit(&b);
// Do we have escape squares from queen contact check attack ?
if (!(escapeSquares & ~queen_attacks_bb(to, occ & ClearMaskBB[ksq])))
{
// We have a mate, unless the queen is pinned or there
// is an X-ray attack through the queen.
for (int i = 0; i < pos.piece_count(Them, QUEEN); i++)
{
from = pos.piece_list(Them, QUEEN, i);
if ( bit_is_set(pos.attacks_from<QUEEN>(from), to)
&& !bit_is_set(pos.pinned_pieces(Them), from)
&& !(rook_attacks_bb(to, occ & ClearMaskBB[from]) & pos.pieces(ROOK, QUEEN, Us))
&& !(bishop_attacks_bb(to, occ & ClearMaskBB[from]) & pos.pieces(BISHOP, QUEEN, Us)))
// Set the mate threat move
ei.mateThreat[Them] = make_move(from, to);
}
}
}
}
}
}
// Analyse enemy's safe distance checks
// Analyse enemy's safe distance checks for sliders and knights
safe = ~(pos.pieces_of_color(Them) | ei.attacked_by(Us));
b1 = pos.attacks_from<ROOK>(ksq) & safe;
b2 = pos.attacks_from<BISHOP>(ksq) & safe;
// Enemy queen safe checks
b = (b1 | b2) & ei.attacked_by(Them, QUEEN);
if (b)
attackUnits += QueenCheckBonus * count_1s_max_15<HasPopCnt>(b);
// Enemy rooks safe checks
b = b1 & ei.attacked_by(Them, ROOK);
if (b)
@ -799,31 +757,18 @@ namespace {
if (b)
attackUnits += BishopCheckBonus * count_1s_max_15<HasPopCnt>(b);
// Enemy queens safe checks
b = (b1 | b2) & ei.attacked_by(Them, QUEEN);
if (b)
attackUnits += QueenCheckBonus * count_1s_max_15<HasPopCnt>(b);
// Enemy knights safe checks
b = pos.attacks_from<KNIGHT>(ksq) & ei.attacked_by(Them, KNIGHT) & safe;
if (b)
attackUnits += KnightCheckBonus * count_1s_max_15<HasPopCnt>(b);
// Analyse discovered checks (only for non-pawns right now, consider
// adding pawns later).
// Analyse enemy's discovered checks (only for non-pawns right now,
// consider adding pawns later).
b = pos.discovered_check_candidates(Them) & ~pos.pieces(PAWN);
if (b)
attackUnits += DiscoveredCheckBonus * count_1s_max_15<HasPopCnt>(b) * (sente ? 2 : 1);
// Has a mate threat been found? We don't do anything here if the
// side with the mating move is the side to move, because in that
// case the mating side will get a huge bonus at the end of the main
// evaluation function instead.
if (ei.mateThreat[Them] != MOVE_NONE)
attackUnits += MateThreatBonus;
// Ensure that attackUnits is between 0 and 99, in order to avoid array
// out of bounds errors.
// To index KingDangerTable[] attackUnits must be in [0, 99] range
attackUnits = Min(99, Max(0, attackUnits));
// Finally, extract the king danger score from the KingDangerTable[]

3
src/evaluate.h
View file

@ -89,9 +89,6 @@ struct EvalInfo {
// 2 to kingAdjacentZoneAttacksCount[BLACK].
int kingAdjacentZoneAttacksCount[2];
// mateThreat[color] is a move for the given side which gives a direct mate.
Move mateThreat[2];
// Middle game and endgame mobility scores
Score mobility;