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Refactor pawns shelter and storm

Browse source 
Renamed stuff and added comments. The aim is to make more
readable, at least by me ;-) , this newly added part of code.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2012-03-28 12:44:41 +02:00
parent 76622342ec
commit 10e64e0509
4 changed files with 68 additions and 63 deletions
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10
src/bitboard.h
View file

@ -263,16 +263,6 @@ extern Square pop_1st_bit(Bitboard* b);
#endif
// relative_rank() returns the relative rank of the closest bit set on the Bitboard.
// Only to be used with bitboards that contain a single file.
template<Color Us>
inline Rank relative_rank(Bitboard b) {
Square s = Us == WHITE ? first_1(b)
: ~last_1(b);
return rank_of(s);
}
extern void print_bitboard(Bitboard b);
extern void bitboards_init();

6
src/evaluate.cpp
View file

@ -751,8 +751,8 @@ Value do_evaluate(const Position& pos, Value& margin) {
int attackUnits;
const Square ksq = pos.king_square(Us);
// King shelter
Score score = ei.pi->king_shelter<Us>(pos, ksq);
// King shelter and enemy pawns storm
Score score = ei.pi->king_safety<Us>(pos, ksq);
// King safety. This is quite complicated, and is almost certainly far
// from optimally tuned.
@ -774,7 +774,7 @@ Value do_evaluate(const Position& pos, Value& margin) {
attackUnits = std::min(25, (ei.kingAttackersCount[Them] * ei.kingAttackersWeight[Them]) / 2)
+ 3 * (ei.kingAdjacentZoneAttacksCount[Them] + popcount<Max15>(undefended))
+ InitKingDanger[relative_square(Us, ksq)]
- mg_value(ei.pi->king_shelter<Us>(pos, ksq)) / 32;
- mg_value(ei.pi->king_safety<Us>(pos, ksq)) / 32;
// Analyse enemy's safe queen contact checks. First find undefended
// squares around the king attacked by enemy queen...

104
src/pawns.cpp
View file

@ -65,18 +65,21 @@ namespace {
#undef S
const File ShelterFile[8] = { FILE_B, FILE_B, FILE_C, FILE_D, FILE_E, FILE_F, FILE_G, FILE_G };
inline Value score_non_center_file(const Value v) {
return Value(v * 7 / 16);
}
typedef Value V;
// Arrays are indexed by rank. Zeroth value is for when no pawn on that file.
const Value PawnShelter[8] = { V(141), V(0), V( 38), V(102), V(128), V(141), V(141), V(141) };
const Value PawnStorm[8] = { V( 26), V(0), V(128), V( 51), V( 26), V( 0), V( 0), V( 0) };
// We compute shelter as a penalty for the given color, but shelter is used as a bonus, so we invert it using this as the basis.
const Value PawnShelterBasis = PawnShelter[0] + score_non_center_file(PawnShelter[0]) * 2;
// Weakness of our pawn shelter in front of the king indexed by [king pawn][rank]
const Value ShelterWeakness[2][8] =
{ { V(141), V(0), V(38), V(102), V(128), V(141), V(141), V(141) },
{ V( 61), V(0), V(16), V( 44), V( 56), V( 61), V( 61), V( 61) } };
// Danger of enemy pawns moving toward our king indexed by [pawn blocked][rank]
const Value StormDanger[2][8] =
{ { V(26), V(0), V(128), V(51), V(26), V(0), V(0), V(0) },
{ V(13), V(0), V( 64), V(25), V(13), V(0), V(0), V(0) } };
// Max bonus for king safety. Corresponds to start position with all the pawns
// in front of the king and no enemy pawns on the horizont.
const Value MaxSafetyBonus = V(263);
inline Score apply_weight(Score v, Score w) {
return make_score((int(mg_value(v)) * mg_value(w)) / 0x100,
@ -222,58 +225,67 @@ Score PawnInfoTable::evaluate_pawns(const Position& pos, Bitboard ourPawns,
return value;
}
template<Color Us>
int computePawnShelter(const Position &pos, Square ksq) {
const Color Them = (Us == WHITE ? BLACK : WHITE);
const File kingFile = ShelterFile[file_of(ksq)];
const Bitboard ourPawns = pos.pieces(PAWN, Us) & in_front_bb(Us, ksq);
const Bitboard theirPawns = pos.pieces(PAWN, Them) & (RankBB[rank_of(ksq)] | in_front_bb(Us, ksq));
int PawnInfo::shelter_storm(const Position& pos, Square ksq) {
int shelter = 0;
const Color Them = (Us == WHITE ? BLACK : WHITE);
// Compute king shelter and storm values for the file the king is on, as well as the two adjacent files.
for (int fileOffset = -1; fileOffset <= 1; fileOffset++) {
// Shelter takes full penalty for center file, otherwise it's half penalty
Bitboard shelterFile = ourPawns & FileBB[kingFile + fileOffset];
Rank shelterClosest = shelterFile ? relative_rank<Us>(shelterFile)
: RANK_1;
int safety = 0;
Bitboard b = pos.pieces(PAWN) & (in_front_bb(Us, ksq) | RankBB[rank_of(ksq)]);
Bitboard ourPawns = b & pos.pieces(Us) & ~RankBB[rank_of(ksq)];
Bitboard theirPawns = b & pos.pieces(Them);
Rank rkUs, rkThem;
File kf = file_of(ksq);
shelter += fileOffset == 0 ? PawnShelter[shelterClosest]
: score_non_center_file(PawnShelter[shelterClosest]);
// Compute shelter and storm values for the file the king is on, as well as
// the two adjacent files. Computation is done from the white point of view.
kf = (kf == FILE_A) ? kf++ : (kf == FILE_H) ? kf-- : kf;
// Storm takes full penalty, unless there is an enemy pawn blocking us
Bitboard stormFile = theirPawns & FileBB[kingFile + fileOffset];
Rank stormClosest = stormFile ? relative_rank<Us>(stormFile)
: RANK_1;
for (int f = kf - 1; f <= kf + 1; f++)
{
// Shelter penalty is higher for the pawn in front of the king
b = ourPawns & FileBB[f];
rkUs = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
safety -= ShelterWeakness[f != kf][rkUs];
shelter += shelterClosest + 1 == stormClosest ? PawnStorm[stormClosest] / 2
: PawnStorm[stormClosest];
// Storm danger is smaller if enemy pawn is blocked
b = theirPawns & FileBB[f];
rkThem = b ? rank_of(Us == WHITE ? first_1(b) : ~last_1(b)) : RANK_1;
safety -= StormDanger[rkThem == rkUs + 1][rkThem];
}
return shelter;
return safety;
}
/// PawnInfo::updateShelter() calculates and caches king shelter. It is called
/// only when king square changes, about 20% of total king_shelter() calls.
/// PawnInfo::update_safety() calculates and caches a bonus for king safety. It is
/// called only when king square changes, about 20% of total king_safety() calls.
template<Color Us>
Score PawnInfo::updateShelter(const Position& pos, Square ksq) {
int shelter = 0;
Score PawnInfo::update_safety(const Position& pos, Square ksq) {
int bonus = 0;
if (relative_rank(Us, ksq) <= RANK_4)
{
shelter = computePawnShelter<Us>(pos, ksq);
if (pos.can_castle(Us == WHITE ? WHITE_OO : BLACK_OO))
shelter = std::min(shelter, computePawnShelter<Us>(pos, relative_square(Us, SQ_G1)));
if (pos.can_castle(Us == WHITE ? WHITE_OOO : BLACK_OOO))
shelter = std::min(shelter, computePawnShelter<Us>(pos, relative_square(Us, SQ_C1)));
shelter = PawnShelterBasis - shelter;
bonus = shelter_storm<Us>(pos, ksq);
// If we can castle use the bonus after the castle if is bigger
if (pos.can_castle(Us == WHITE ? WHITE_OO : BLACK_OO))
bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_G1)));
if (pos.can_castle(Us == WHITE ? WHITE_OOO : BLACK_OOO))
bonus = std::max(bonus, shelter_storm<Us>(pos, relative_square(Us, SQ_C1)));
bonus += MaxSafetyBonus; // Offset to be sure bonus is always positive
}
kingSquares[Us] = ksq;
kingShelters[Us] = make_score(shelter, 0);
kingShelters[Us] = make_score(bonus, 0);
return kingShelters[Us];
}
// Explicit template instantiation
template Score PawnInfo::updateShelter<WHITE>(const Position& pos, Square ksq);
template Score PawnInfo::updateShelter<BLACK>(const Position& pos, Square ksq);
template Score PawnInfo::update_safety<WHITE>(const Position& pos, Square ksq);
template Score PawnInfo::update_safety<BLACK>(const Position& pos, Square ksq);

11
src/pawns.h
View file

@ -46,11 +46,14 @@ public:
int has_open_file_to_right(Color c, File f) const;
template<Color Us>
Score king_shelter(const Position& pos, Square ksq);
Score king_safety(const Position& pos, Square ksq);
private:
template<Color Us>
Score updateShelter(const Position& pos, Square ksq);
Score update_safety(const Position& pos, Square ksq);
template<Color Us>
int shelter_storm(const Position& pos, Square ksq);
Key key;
Bitboard passedPawns[2];
@ -100,8 +103,8 @@ inline int PawnInfo::has_open_file_to_right(Color c, File f) const {
}
template<Color Us>
inline Score PawnInfo::king_shelter(const Position& pos, Square ksq) {
return kingSquares[Us] == ksq ? kingShelters[Us] : updateShelter<Us>(pos, ksq);
inline Score PawnInfo::king_safety(const Position& pos, Square ksq) {
return kingSquares[Us] == ksq ? kingShelters[Us] : update_safety<Us>(pos, ksq);
}
#endif // !defined(PAWNS_H_INCLUDED)