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Remove KNPKB endgame.

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This is a functional simplification that removes the KNPKB endgame.

Testing on only KNPKB positions suggests that this removal actually gains Elo:

Score of patch vs master: 3380 - 3035 - 33585  [0.504] 40000
Elo difference: 3.0 +/- 1.4, LOS: 100.0 %, DrawRatio: 84.0 %

Score of patch vs master: 290 - 36 - 39674  [0.503] 40000
Elo difference: 2.2 +/- 0.3, LOS: 100.0 %, DrawRatio: 99.2 %

removal also doesn't cause a regression with the standard book:

STC
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 71376 W: 13794 L: 13719 D: 43863
Ptnml(0-2): 1066, 8092, 17290, 8181, 1059
https://tests.stockfishchess.org/tests/view/5e76c3d5e42a5c3b3ca2e8be

LTC
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 28394 W: 3731 L: 3662 D: 21001
Ptnml(0-2): 167, 2339, 9116, 2408, 167
https://tests.stockfishchess.org/tests/view/5e76e5eae42a5c3b3ca2e8d3

closes https://github.com/official-stockfish/Stockfish/pull/2594

Bench 5480811
This commit is contained in:
protonspring 2020-03-22 22:21:49 -06:00 • committed by Joost VandeVondele
parent 6ecab03dee
commit 8b229381da
2 changed files with 0 additions and 23 deletions
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22
src/endgame.cpp
View file

@ -80,7 +80,6 @@ namespace Endgames {
add<KNNKP>("KNNKP");
add<KNPK>("KNPK");
add<KNPKB>("KNPKB");
add<KRPKR>("KRPKR");
add<KRPKB>("KRPKB");
add<KBPKB>("KBPKB");
@ -733,27 +732,6 @@ ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {
}
/// KNP vs KB. If knight can block bishop from taking pawn, it's a win.
/// Otherwise the position is drawn.
template<>
ScaleFactor Endgame<KNPKB>::operator()(const Position& pos) const {
assert(verify_material(pos, strongSide, KnightValueMg, 1));
assert(verify_material(pos, weakSide, BishopValueMg, 0));
Square pawnSq = pos.square<PAWN>(strongSide);
Square bishopSq = pos.square<BISHOP>(weakSide);
Square weakKingSq = pos.square<KING>(weakSide);
// King needs to get close to promoting pawn to prevent knight from blocking.
// Rules for this are very tricky, so just approximate.
if (forward_file_bb(strongSide, pawnSq) & pos.attacks_from<BISHOP>(bishopSq))
return ScaleFactor(distance(weakKingSq, pawnSq));
return SCALE_FACTOR_NONE;
}
/// KP vs KP. This is done by removing the weakest side's pawn and probing the
/// KP vs K bitbase: If the weakest side has a draw without the pawn, it probably
/// has at least a draw with the pawn as well. The exception is when the stronger

1
src/endgame.h
View file

@ -58,7 +58,6 @@ enum EndgameCode {
KBPPKB, // KBPP vs KB
KBPKN, // KBP vs KN
KNPK, // KNP vs K
KNPKB, // KNP vs KB
KPKP // KP vs KP
};