deepcrayon
/
stockfish
1
0
Fork 0
Code Releases Activity

Further smplify pawn endgames 

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.
sf_dd_base
Marco Costalba 2013-10-23 15:50:20 +02:00
parent 3674f18b97
commit 67b0da83da
2 changed files with 29 additions and 38 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

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;
};