kate/BadFish
1
0
Fork 0
mirror of https://github.com/sockspls/badfish synced 2025-07-11 19:49:14 +00:00
Code Issues Releases Wiki Activity

Improve endgame KBN vs K (#1877)

Browse source 
Even when playing without endgame table bases, this particular endgame should
be a win 100% of the time when Stockfish is given a KRBK position, assuming
there are enough moves remaining in the FEN to finish the game without hitting
the 50 move rule.

PROBLEM: The issue with master here is that the PushClose difference per square
is 20, however, the difference in squares for the PushToCorners array is usually
less. Thus, the engine prefers to move the kings closer together rather than pushing
the weak king to the correct corner.

What happens is if the weak king is in a safe corner, SF still prefers pushing the
kings together. Occasionally, the strong king traps the weak king in the safe corner.
It takes a while for SF to figure it out, but often draws the game by the 50 move rule
(on shorter time controls).

This patch increases the PushToCorners values to correct this problem. We also added
an assert to catch any overflow problem if anybody would want to increase the array
values again in the future.

It was tested in a couple of matches starting with random KRBK positions and showed
increased winning rates, see https://github.com/official-stockfish/Stockfish/pull/1877

No functional change
This commit is contained in:
protonspring 2018-12-17 10:25:25 -07:00 • committed by Stéphane Nicolet
parent 2089c414da
commit 96ac85b319
1 changed files with 9 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

17
src/endgame.cpp
View file

@ -45,14 +45,14 @@ namespace {
// Table used to drive the king towards a corner square of the
// right color in KBN vs K endgames.
constexpr int PushToCorners[SQUARE_NB] = {
200, 190, 180, 170, 160, 150, 140, 130,
190, 180, 170, 160, 150, 140, 130, 140,
180, 170, 155, 140, 140, 125, 140, 150,
170, 160, 140, 120, 110, 140, 150, 160,
160, 150, 140, 110, 120, 140, 160, 170,
150, 140, 125, 140, 140, 155, 170, 180,
140, 130, 140, 150, 160, 170, 180, 190,
130, 140, 150, 160, 170, 180, 190, 200
6400, 6080, 5760, 5440, 5120, 4800, 4480, 4160,
6080, 5760, 5440, 5120, 4800, 4480, 4160, 4480,
5760, 5440, 4960, 4480, 4480, 4000, 4480, 4800,
5440, 5120, 4480, 3840, 3520, 4480, 4800, 5120,
5120, 4800, 4480, 3520, 3840, 4480, 5120, 5440,
4800, 4480, 4000, 4480, 4480, 4960, 5440, 5760,
4480, 4160, 4480, 4800, 5120, 5440, 5760, 6080,
4160, 4480, 4800, 5120, 5440, 5760, 6080, 6400
};
// Tables used to drive a piece towards or away from another piece
@ -138,6 +138,7 @@ Value Endgame<KBNK>::operator()(const Position& pos) const {
+ PushClose[distance(winnerKSq, loserKSq)]
+ PushToCorners[opposite_colors(bishopSq, SQ_A1) ? ~loserKSq : loserKSq];
assert(abs(result) < VALUE_MATE_IN_MAX_PLY);
return strongSide == pos.side_to_move() ? result : -result;
}