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Fix check for bishop pair in material imbalance

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Prefer pos.bishop_pair() to pos.count<BISHOP>(WHITE) > 1
because the first checks that the two bishops are on
different color squares.

Although the change seems to kick in only in very rare cases,
quite surprisingly it was able to pass SPRT test at short TC.

LLR: 2.95 (-2.94,2.94)
Total: 39818 W: 8174 L: 7956 D: 23688

bench: 3453941
This commit is contained in:
Eelco de Groot 2013-09-02 22:50:32 +02:00 • committed by Marco Costalba
parent 9ff594c3a9
commit 679c2ea227
1 changed files with 5 additions and 5 deletions
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10
src/material.cpp
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@ -263,14 +263,14 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
e->spaceWeight = make_score(minorPieceCount * minorPieceCount, 0);
}
// Evaluate the material imbalance. We use PIECE_TYPE_NONE as a place holder
// Evaluate the material imbalance. We use NO_PIECE_TYPE as a place holder
// for the bishop pair "extended piece", this allow us to be more flexible
// in defining bishop pair bonuses.
const int pieceCount[COLOR_NB][PIECE_TYPE_NB] = {
{ pos.count<BISHOP>(WHITE) > 1, pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
pos.count<BISHOP>(WHITE) , pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
{ pos.count<BISHOP>(BLACK) > 1, pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
pos.count<BISHOP>(BLACK) , pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
{ pos.bishop_pair(WHITE) , pos.count<PAWN>(WHITE), pos.count<KNIGHT>(WHITE),
pos.count<BISHOP>(WHITE), pos.count<ROOK>(WHITE), pos.count<QUEEN >(WHITE) },
{ pos.bishop_pair(BLACK) , pos.count<PAWN>(BLACK), pos.count<KNIGHT>(BLACK),
pos.count<BISHOP>(BLACK), pos.count<ROOK>(BLACK), pos.count<QUEEN >(BLACK) } };
e->value = (int16_t)((imbalance<WHITE>(pieceCount) - imbalance<BLACK>(pieceCount)) / 16);
return e;