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Add bonus for pawn attack threats 

Latent pawn attacks: Add a bonus to safe pawn pushes which attacks an
enemy piece.  Based on an idea of Lyudmil Tsvetkov.

STC:
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 7925 W: 1666 L: 1537 D: 4722

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 40109 W: 6841 L: 6546 D: 26722

Bench: 7696257

Resolves #240
pull/240/merge
Stefan Geschwentner 2015-02-03 11:16:50 +08:00 committed by Gary Linscott
parent f4136c5434
commit 18b0809639
1 changed files with 22 additions and 1 deletions
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23
src/evaluate.cpp
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@ -162,6 +162,7 @@ namespace {
const Score TrappedRook = S(92, 0);
const Score Unstoppable = S( 0, 20);
const Score Hanging = S(31, 26);
const Score PawnAttackThreat = S(20, 20);
// Penalty for a bishop on a1/h1 (a8/h8 for black) which is trapped by
// a friendly pawn on b2/g2 (b7/g7 for black). This can obviously only
@ -492,7 +493,12 @@ namespace {
template<Color Us, bool Trace>
Score evaluate_threats(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);
const Square Left = (Us == WHITE ? DELTA_NW : DELTA_SE);
const Square Right = (Us == WHITE ? DELTA_NE : DELTA_SW);
const Bitboard TRank2BB = (Us == WHITE ? Rank2BB : Rank7BB);
const Bitboard TRank7BB = (Us == WHITE ? Rank7BB : Rank2BB);
enum { Defended, Weak };
enum { Minor, Major };
@ -541,6 +547,21 @@ namespace {
score += more_than_one(b) ? KingOnMany : KingOnOne;
}
// Add bonus for safe pawn pushes which attacks an enemy piece
b = pos.pieces(Us, PAWN) & ~TRank7BB;
b = shift_bb<Up>(b | (shift_bb<Up>(b & TRank2BB) & ~pos.pieces()));
b &= ~pos.pieces()
& ~ei.attackedBy[Them][PAWN]
& (ei.attackedBy[Us][PAWN] | ~ei.attackedBy[Them][ALL_PIECES]);
b = (shift_bb<Left>(b) | shift_bb<Right>(b))
& pos.pieces(Them)
& ~ei.attackedBy[Us][PAWN];
if(b)
score += popcount<Max15>(b) * PawnAttackThreat;
if (Trace)
Tracing::write(Tracing::THREAT, Us, score);