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Calculate maximum threat for hanging pieces 

Use the max_threat() helper function to estimate more precisely the
best hanging piece threat.  Also retunes the Threat array using SPSA.

STC
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 7598 W: 1596 L: 1468 D: 4534

LTC
LLR: 2.97 (-2.94,2.94) [0.00,6.00]
Total: 7896 W: 1495 L: 1350 D: 5051

Bench: 6816504

Resolves #73
pull/73/merge
snicolet 2014-10-24 01:10:11 +08:00 committed by Gary Linscott
parent 480682b670
commit 8d62ece945
1 changed files with 23 additions and 5 deletions
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28
src/evaluate.cpp
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@ -141,8 +141,8 @@ namespace {
// Threat[attacking][attacked] contains bonuses according to which piece
// type attacks which one.
const Score Threat[][PIECE_TYPE_NB] = {
{ S(0, 0), S( 7, 39), S(24, 49), S(24, 49), S(41,100), S(41,100) }, // Minor
{ S(0, 0), S(15, 39), S(15, 45), S(15, 45), S(15, 45), S(24, 49) } // Major
{ S(0, 0), S(0, 38), S(32, 45), S(32, 45), S(41,100), S(35,104) }, // Minor
{ S(0, 0), S(7, 28), S(20, 49), S(20, 49), S(8 , 42), S(23, 44) } // Major
};
// ThreatenedByPawn[PieceType] contains a penalty according to which piece
@ -490,6 +490,23 @@ namespace {
return score;
}
// max_threat() is a helper function to calculate the score of a set of threats.
// The set of threatened pieces is in the "targets" parameter, and we return
// the value of the threat on the biggest piece.
template<Color Us> FORCE_INLINE
Score max_threat(const Bitboard targets, const Position& pos, const Score threat_values[]) {
const Color Them = (Us == WHITE ? BLACK : WHITE);
PieceType threat = PAWN;
if (targets & pos.pieces(Them, KNIGHT)) threat = KNIGHT;
if (targets & pos.pieces(Them, BISHOP)) threat = BISHOP;
if (targets & pos.pieces(Them, ROOK)) threat = ROOK;
if (targets & pos.pieces(Them, QUEEN)) threat = QUEEN;
return threat_values[threat];
}
// evaluate_threats() assigns bonuses according to the type of attacking piece
// and the type of attacked one.
@ -509,7 +526,8 @@ namespace {
& (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
if (protectedEnemies)
score += Threat[Minor][type_of(pos.piece_on(lsb(protectedEnemies)))];
score += max_threat<Us>(protectedEnemies, pos, Threat[Minor]);
// Enemies not defended by a pawn and under our attack
weakEnemies = pos.pieces(Them)
@ -521,11 +539,11 @@ namespace {
{
b = weakEnemies & (ei.attackedBy[Us][KNIGHT] | ei.attackedBy[Us][BISHOP]);
if (b)
score += Threat[Minor][type_of(pos.piece_on(lsb(b)))];
score += max_threat<Us>(b, pos, Threat[Minor]);
b = weakEnemies & (ei.attackedBy[Us][ROOK] | ei.attackedBy[Us][QUEEN]);
if (b)
score += Threat[Major][type_of(pos.piece_on(lsb(b)))];
score += max_threat<Us>(b, pos, Threat[Major]);
b = weakEnemies & ~ei.attackedBy[Them][ALL_PIECES];
if (b)