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Code Issues Releases Wiki Activity

Further smplify pawn endgames

Browse source 
Dumb down a bit the code and trade some possible
speed (but this is far from hot path anyhow) for
some added readability for the layman.

No functional change.
This commit is contained in:
Marco Costalba 2013-10-23 15:50:20 +02:00
parent 3674f18b97
commit 67b0da83da
2 changed files with 29 additions and 38 deletions
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65
src/endgame.cpp
View file

@ -65,6 +65,21 @@ namespace {
}
#endif
// Map the square as if strongSide is white and strongSide's only pawn
// is on the left half of the board.
Square normalize(const Position& pos, Color strongSide, Square sq) {
assert(pos.count<PAWN>(strongSide) == 1);
if (file_of(pos.list<PAWN>(strongSide)[0]) >= FILE_E)
sq = mirror(sq);
if (strongSide == BLACK)
sq = ~sq;
return sq;
}
// Get the material key of a Position out of the given endgame key code
// like "KBPKN". The trick here is to first forge an ad-hoc fen string
// and then let a Position object to do the work for us. Note that the
@ -188,22 +203,6 @@ Value Endgame<KBNK>::operator()(const Position& pos) const {
return strongSide == pos.side_to_move() ? result : -result;
}
// Returns a square that will allow us to orient the board so that
// strongSide is white and strongSide's only pawn is on the left
// half of the board
Square get_flip_sq(const Position& pos, Color strongSide) {
assert(pos.count<PAWN>(strongSide) == 1);
Square psq = pos.list<PAWN>(strongSide)[0];
return (FILE_H * (file_of(psq) >= FILE_E)) | (RANK_8 * int(strongSide));
}
Square operator^(Square s, Square flip_sq) {
assert(flip_sq == SQ_A1 || flip_sq == SQ_H1 || flip_sq == SQ_A8 || flip_sq == SQ_H8);
return Square(int(s) ^ int(flip_sq));
}
/// KP vs K. This endgame is evaluated with the help of a bitbase.
template<>
@ -213,11 +212,9 @@ Value Endgame<KPK>::operator()(const Position& pos) const {
assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
// Assume strongSide is white and the pawn is on files A-D
Square flip_sq = get_flip_sq(pos, strongSide);
Square wksq = pos.king_square(strongSide) ^ flip_sq;
Square bksq = pos.king_square(weakSide) ^ flip_sq;
Square psq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
Square psq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;
@ -484,13 +481,11 @@ ScaleFactor Endgame<KRPKR>::operator()(const Position& pos) const {
assert(verify_material(pos, weakSide, RookValueMg, 0));
// Assume strongSide is white and the pawn is on files A-D
Square flip_sq = get_flip_sq(pos, strongSide);
Square wksq = pos.king_square(strongSide) ^ flip_sq;
Square bksq = pos.king_square(weakSide) ^ flip_sq;
Square wrsq = pos.list<ROOK>(strongSide)[0] ^ flip_sq;
Square wpsq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
Square brsq = pos.list<ROOK>(weakSide)[0] ^ flip_sq;
Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
Square wrsq = normalize(pos, strongSide, pos.list<ROOK>(strongSide)[0]);
Square wpsq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
Square brsq = normalize(pos, strongSide, pos.list<ROOK>(weakSide)[0]);
File f = file_of(wpsq);
Rank r = rank_of(wpsq);
@ -833,10 +828,8 @@ ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {
assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
// Assume strongSide is white and the pawn is on files A-D
Square flip_sq = get_flip_sq(pos, strongSide);
Square pawnSq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
Square weakKingSq = pos.king_square(weakSide) ^ flip_sq;
Square pawnSq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
Square weakKingSq = normalize(pos, strongSide, pos.king_square(weakSide));
if (pawnSq == SQ_A7 && square_distance(SQ_A8, weakKingSq) <= 1)
return SCALE_FACTOR_DRAW;
@ -875,11 +868,9 @@ ScaleFactor Endgame<KPKP>::operator()(const Position& pos) const {
assert(verify_material(pos, weakSide, VALUE_ZERO, 1));
// Assume strongSide is white and the pawn is on files A-D
Square flip_sq = get_flip_sq(pos, strongSide);
Square wksq = pos.king_square(strongSide) ^ flip_sq;
Square bksq = pos.king_square(weakSide) ^ flip_sq;
Square psq = pos.list<PAWN>(strongSide)[0] ^ flip_sq;
Square wksq = normalize(pos, strongSide, pos.king_square(strongSide));
Square bksq = normalize(pos, strongSide, pos.king_square(weakSide));
Square psq = normalize(pos, strongSide, pos.list<PAWN>(strongSide)[0]);
Color us = strongSide == pos.side_to_move() ? WHITE : BLACK;

2
src/endgame.h
View file

@ -91,7 +91,7 @@ struct Endgame : public EndgameBase<T> {
T operator()(const Position&) const;
private:
Color strongSide, weakSide;
const Color strongSide, weakSide;
};