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Space bonus in presence of open files

Browse source 
If the opponent has a cramped position, opening a file often
helps him/her to exchange pieces, so it makes sense to reduce
the space bonus if there are open files.

Credits: Leonardo Ljubičić for the strategic idea, Alain Savard for the
implementation of the open files calculation, "CrunchyNYC" for the
compensation of the numerator.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 49112 W: 9239 L: 8900 D: 30973

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 89415 W: 12014 L: 11601 D: 65800

Bench: 7591630
This commit is contained in:
Stéphane Nicolet 2016-09-03 00:04:20 +02:00
parent 13b4444d9e
commit d37dfe9ae4
3 changed files with 5 additions and 2 deletions
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4
src/evaluate.cpp
View file

@ -706,9 +706,9 @@ namespace {
// ...count safe + (behind & safe) with a single popcount
int bonus = popcount((Us == WHITE ? safe << 32 : safe >> 32) | (behind & safe));
bonus = std::min(16, bonus);
int weight = pos.count<ALL_PIECES>(Us);
int weight = pos.count<ALL_PIECES>(Us) - 2 * ei.pi->open_files();
return make_score(bonus * weight * weight / 22, 0);
return make_score(bonus * weight * weight / 18, 0);
}

1
src/pawns.cpp
View file

@ -215,6 +215,7 @@ Entry* probe(const Position& pos) {
e->key = key;
e->score = evaluate<WHITE>(pos, e) - evaluate<BLACK>(pos, e);
e->asymmetry = popcount(e->semiopenFiles[WHITE] ^ e->semiopenFiles[BLACK]);
e->openFiles = popcount(e->semiopenFiles[WHITE] & e->semiopenFiles[BLACK]);
return e;
}

2
src/pawns.h
View file

@ -38,6 +38,7 @@ struct Entry {
Bitboard passed_pawns(Color c) const { return passedPawns[c]; }
Bitboard pawn_attacks_span(Color c) const { return pawnAttacksSpan[c]; }
int pawn_asymmetry() const { return asymmetry; }
int open_files() const { return openFiles; }
int semiopen_file(Color c, File f) const {
return semiopenFiles[c] & (1 << f);
@ -74,6 +75,7 @@ struct Entry {
int semiopenFiles[COLOR_NB];
int pawnsOnSquares[COLOR_NB][COLOR_NB]; // [color][light/dark squares]
int asymmetry;
int openFiles;
};
typedef HashTable<Entry, 16384> Table;