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Count two times number of attacked pieces in mobility

Now in mobility we count enemy attacked pieces as
empty squares.

With this patch we try to give an higher score to positions
where the number of attacked pieces is higher.

After 999 games at 1+0

Mod vs Orig +262 =517 -219 52.15% 520.5/998 +15 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
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1 parent a6c6037 commit cff9ff21985edcf1d15e7df6c0e0039f550706ad @mcostalba committed Sep 28, 2009
Showing with 25 additions and 13 deletions.
  1. +25 −13 src/evaluate.cpp
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@@ -529,31 +529,43 @@ namespace {
// evaluate_mobility() computes mobility and attacks for every piece
template<PieceType Piece, Color Us, bool HasPopCnt>
- int evaluate_mobility(const Position& pos, const Bitboard& mob_bb, EvalInfo& ei) {
+ int evaluate_mobility(const Position& pos, Bitboard b, EvalInfo& ei) {
const Color Them = (Us == WHITE ? BLACK : WHITE);
static const int AttackWeight[] = { 0, 0, KnightAttackWeight, BishopAttackWeight, RookAttackWeight, QueenAttackWeight };
static const Value* MgBonus[] = { 0, 0, MidgameKnightMobilityBonus, MidgameBishopMobilityBonus, MidgameRookMobilityBonus, MidgameQueenMobilityBonus };
static const Value* EgBonus[] = { 0, 0, EndgameKnightMobilityBonus, EndgameBishopMobilityBonus, EndgameRookMobilityBonus, EndgameQueenMobilityBonus };
+ static const int lastIndex[] = { 0, 0, 8, 15, 15, 31 };
// Update attack info
- ei.attackedBy[Us][Piece] |= mob_bb;
+ ei.attackedBy[Us][Piece] |= b;
// King attacks
- if (mob_bb & ei.kingZone[Us])
+ if (b & ei.kingZone[Us])
{
ei.kingAttackersCount[Us]++;
ei.kingAttackersWeight[Us] += AttackWeight[Piece];
- Bitboard b = (mob_bb & ei.attackedBy[Them][KING]);
- if (b)
- ei.kingAdjacentZoneAttacksCount[Us] += count_1s_max_15<HasPopCnt>(b);
+ Bitboard bb = (b & ei.attackedBy[Them][KING]);
+ if (bb)
+ ei.kingAdjacentZoneAttacksCount[Us] += count_1s_max_15<HasPopCnt>(bb);
}
+ // The squares occupied by enemy pieces will be counted two times instead
+ // of one. The shift (almost) guarantees that intersection with b is zero
+ // so when we 'or' the two bitboards togheter and count we get the correct
+ // sum of '1' in b and attacked bitboards.
+ Bitboard attacked = Us == WHITE ? ((b & pos.pieces_of_color(Them)) >> 1)
+ : ((b & pos.pieces_of_color(Them)) << 1);
+
// Remove squares protected by enemy pawns or occupied by our pieces
- Bitboard b = mob_bb & ~ei.attackedBy[Them][PAWN] & ~pos.pieces_of_color(Us);
+ b &= ~(ei.attackedBy[Them][PAWN] | pos.pieces_of_color(Us));
// Mobility
- int mob = (Piece != QUEEN ? count_1s_max_15<HasPopCnt>(b) : count_1s<HasPopCnt>(b));
+ int mob = (Piece != QUEEN ? count_1s_max_15<HasPopCnt>(b | attacked)
+ : count_1s<HasPopCnt>(b | attacked));
+
+ if (mob > lastIndex[Piece])
+ mob = lastIndex[Piece];
ei.mgMobility += Sign[Us] * MgBonus[Piece][mob];
ei.egMobility += Sign[Us] * EgBonus[Piece][mob];
@@ -592,7 +604,7 @@ namespace {
template<PieceType Piece, Color Us, bool HasPopCnt>
void evaluate_pieces(const Position& pos, EvalInfo& ei) {
- Bitboard mob_bb;
+ Bitboard b;
Square s, ksq;
int mob;
File f;
@@ -603,16 +615,16 @@ namespace {
while ((s = *ptr++) != SQ_NONE)
{
if (Piece == KNIGHT || Piece == QUEEN)
- mob_bb = pos.attacks_from<Piece>(s);
+ b = pos.attacks_from<Piece>(s);
else if (Piece == BISHOP)
- mob_bb = bishop_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(QUEEN, Us));
+ b = bishop_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(QUEEN, Us));
else if (Piece == ROOK)
- mob_bb = rook_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(ROOK, QUEEN, Us));
+ b = rook_attacks_bb(s, pos.occupied_squares() & ~pos.pieces(ROOK, QUEEN, Us));
else
assert(false);
// Attacks and mobility
- mob = evaluate_mobility<Piece, Us, HasPopCnt>(pos, mob_bb, ei);
+ mob = evaluate_mobility<Piece, Us, HasPopCnt>(pos, b, ei);
// Bishop and knight outposts squares
if ((Piece == BISHOP || Piece == KNIGHT) && pos.square_is_weak(s, Them))

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