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Unsafe checks 

Introducing a new multi-purpose penalty related to King safety, which
includes all kind of potential checks (from unsafe or unavailable
squares currently occupied by some other piece)

This will indirectly detect and reward some pins, discovered checks, and
motifs such as square vacation, or rook behind its pawn and aligned with
King (example Black Rg8, g7 against Kg1),
and penalize some pawn blockers (if they move, it allows a discovered
check by the pawn).

And since it looks also at protected squares, it detects some potential
defense overloading.

Finally, the rook contact checks had been removed some time ago. This
test will give a small bonus for them, as well as for bishop contact
checks.

Passed STC
http://tests.stockfishchess.org/tests/view/5729ec740ebc59301a354b36
LLR: 2.94 (-2.94,2.94) [0.00,5.00]
Total: 13306 W: 2477 L: 2296 D: 8533

and LTC
http://tests.stockfishchess.org/tests/view/572a5be00ebc59301a354b65
LLR: 2.97 (-2.94,2.94) [0.00,5.00]
Total: 20369 W: 2750 L: 2565 D: 15054

bench: 9298175
pull/669/head^2
Alain SAVARD 2016-05-06 09:40:56 -04:00 committed by Marco Costalba
parent 5e4cd3fc0d
commit 4b9ed6566a
1 changed files with 35 additions and 18 deletions
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53
src/evaluate.cpp
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@ -183,7 +183,8 @@ namespace {
const Score BishopPawns = S( 8, 12);
const Score RookOnPawn = S( 8, 24);
const Score TrappedRook = S(92, 0);
const Score Checked = S(20, 20);
const Score SafeCheck = S(20, 20);
const Score OtherCheck = S(10, 10);
const Score ThreatByHangingPawn = S(71, 61);
const Score LooseEnemies = S( 0, 25);
const Score Hanging = S(48, 27);
@ -366,9 +367,10 @@ namespace {
template<Color Us, bool DoTrace>
Score evaluate_king(const Position& pos, const EvalInfo& ei) {
const Color Them = (Us == WHITE ? BLACK : WHITE);
const Color Them = (Us == WHITE ? BLACK : WHITE);
const Square Up = (Us == WHITE ? DELTA_N : DELTA_S);
Bitboard undefended, b, b1, b2, safe;
Bitboard undefended, b, b1, b2, safe, other;
int attackUnits;
const Square ksq = pos.square<KING>(Us);
@ -414,27 +416,42 @@ namespace {
attackUnits += QueenContactCheck * popcount(b);
}
// Analyse the enemy's safe distance checks for sliders and knights
safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
// Analyse the safe enemy's checks which are possible on next move...
safe = ~(ei.attackedBy[Us][ALL_PIECES] | pos.pieces(Them));
b1 = pos.attacks_from<ROOK >(ksq) & safe;
b2 = pos.attacks_from<BISHOP>(ksq) & safe;
// ... and some other potential checks, only requiring the square to be
// safe from pawn-attacks, and not being occupied by a blocked pawn.
other = ~( ei.attackedBy[Us][PAWN]
| (pos.pieces(Them, PAWN) & shift_bb<Up>(pos.pieces(PAWN))));
b1 = pos.attacks_from<ROOK >(ksq);
b2 = pos.attacks_from<BISHOP>(ksq);
// Enemy queen safe checks
if ((b1 | b2) & ei.attackedBy[Them][QUEEN])
attackUnits += QueenCheck, score -= Checked;
if ((b1 | b2) & ei.attackedBy[Them][QUEEN] & safe)
attackUnits += QueenCheck, score -= SafeCheck;
// Enemy rooks safe checks
if (b1 & ei.attackedBy[Them][ROOK])
attackUnits += RookCheck, score -= Checked;
// Enemy rooks safe and other checks
if (b1 & ei.attackedBy[Them][ROOK] & safe)
attackUnits += RookCheck, score -= SafeCheck;
// Enemy bishops safe checks
if (b2 & ei.attackedBy[Them][BISHOP])
attackUnits += BishopCheck, score -= Checked;
else if (b1 & ei.attackedBy[Them][ROOK] & other)
score -= OtherCheck;
// Enemy knights safe checks
if (pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT] & safe)
attackUnits += KnightCheck, score -= Checked;
// Enemy bishops safe and other checks
if (b2 & ei.attackedBy[Them][BISHOP] & safe)
attackUnits += BishopCheck, score -= SafeCheck;
else if (b2 & ei.attackedBy[Them][BISHOP] & other)
score -= OtherCheck;
// Enemy knights safe and other checks
b = pos.attacks_from<KNIGHT>(ksq) & ei.attackedBy[Them][KNIGHT];
if (b & safe)
attackUnits += KnightCheck, score -= SafeCheck;
else if (b & other)
score -= OtherCheck;
// Finally, extract the king danger score from the KingDanger[]
// array and subtract the score from the evaluation.