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remove KNPK endgame code 

In more than 100k local KNPK games, there is no discernible difference between master and master with this endgame removed: master:42971, patch:42973, draws: 3969. Removal does not seem to regress in normal games.

STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 46390 W: 8998 L: 8884 D: 28508
Ptnml(0-2): 707, 5274, 11163, 5300, 751
https://tests.stockfishchess.org/tests/view/5e83b18ee42a5c3b3ca2ef02

LTC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 44768 W: 5863 L: 5814 D: 33091
Ptnml(0-2): 251, 3918, 14028, 3905, 282
https://tests.stockfishchess.org/tests/view/5e84a82a4411759d9d0984f4

In tests with a book of endgames that can convert into KNPK, no significant difference can be seen either

```
TC 1.0+0.01
Score of patch vs master: 6131 - 6188 - 27681  [0.499] 40000
Elo difference: -0.5 +/- 1.9, LOS: 30.4 %, DrawRatio: 69.2 %

TC 2.0+0.02
Score of patch vs master: 5740 - 5741 - 28519 [0.500] 40000
Elo difference: -0.0 +/- 1.8, LOS: 49.6 %, DrawRatio: 71.3 %
``

closes https://github.com/official-stockfish/Stockfish/pull/2611

Bench 4512059
pull/2616/head^2
protonspring 2020-03-31 15:08:55 -06:00 committed by Joost VandeVondele
parent c14f4877cf
commit 3cb1c6c3c6
2 changed files with 0 additions and 21 deletions
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20
src/endgame.cpp
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@ -79,7 +79,6 @@ namespace Endgames {
add<KQKR>("KQKR");
add<KNNKP>("KNNKP");
add<KNPK>("KNPK");
add<KRPKR>("KRPKR");
add<KRPKB>("KRPKB");
add<KBPKB>("KBPKB");
@ -713,25 +712,6 @@ ScaleFactor Endgame<KBPKN>::operator()(const Position& pos) const {
}
/// KNP vs K. There is a single rule: if the pawn is a rook pawn on the 7th rank
/// and the defending king prevents the pawn from advancing, the position is drawn.
template<>
ScaleFactor Endgame<KNPK>::operator()(const Position& pos) const {
assert(verify_material(pos, strongSide, KnightValueMg, 1));
assert(verify_material(pos, weakSide, VALUE_ZERO, 0));
// Assume strongSide is white and the pawn is on files A-D
Square pawnSq = normalize(pos, strongSide, pos.square<PAWN>(strongSide));
Square weakKingSq = normalize(pos, strongSide, pos.square<KING>(weakSide));
if (pawnSq == SQ_A7 && distance(SQ_A8, weakKingSq) <= 1)
return SCALE_FACTOR_DRAW;
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

@ -57,7 +57,6 @@ enum EndgameCode {
KBPKB, // KBP vs KB
KBPPKB, // KBPP vs KB
KBPKN, // KBP vs KN
KNPK, // KNP vs K
KPKP // KP vs KP
};