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Simplify King Evasion

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Simplify away the removal of some illegal `KING`-evasion moves during move
generation. Verified for correctness by running perft on the following positions:

```
./stockfish
bench 16 1 6 default perft
Nodes searched: 71608931810

./stockfish
position fen 4rrk1/1p1nq3/p7/2p1P1pp/3P2bp/3Q1Bn1/PPPB4/1K2R1NR w - - 40 21
go perft 6
Nodes searched: 6136386434
```

Passed STC:
LLR: 2.94 (-2.94,2.94) {-1.00,0.20}
Total: 16072 W: 1473 L: 1349 D: 13250
Ptnml(0-2): 57, 1047, 5710, 1159, 63
https://tests.stockfishchess.org/tests/view/60629e7ef183b42957b423b1

Passed LTC:
LLR: 2.94 (-2.94,2.94) {-0.70,0.20}
Total: 59064 W: 2214 L: 2177 D: 54673
Ptnml(0-2): 26, 1944, 25556, 1979, 27
https://tests.stockfishchess.org/tests/view/6062dce4f183b42957b423de

closes https://github.com/official-stockfish/Stockfish/pull/3415

No functional change
This commit is contained in:
bmc4
2021-03-30 00:42:45 -03:00
committed by Stéphane Nicolet
parent 62a0b65ff8
commit c489df6f5b
2 changed files with 3 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
src/movegen.cpp
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@@ -313,17 +313,9 @@ ExtMove* generate<EVASIONS>(const Position& pos, ExtMove* moveList) {
Color us = pos.side_to_move();
Square ksq = pos.square<KING>(us);
Bitboard sliderAttacks = 0;
Bitboard sliders = pos.checkers() & ~pos.pieces(KNIGHT, PAWN);
// Find all the squares attacked by slider checkers. We will remove them from
// the king evasions in order to skip known illegal moves, which avoids any
// useless legality checks later on.
while (sliders)
sliderAttacks |= line_bb(ksq, pop_lsb(sliders)) & ~pos.checkers();
// Generate evasions for king, capture and non capture moves
Bitboard b = attacks_bb<KING>(ksq) & ~pos.pieces(us) & ~sliderAttacks;
// Generate evasions for king
Bitboard b = attacks_bb<KING>(ksq) & ~pos.pieces(us);
while (b)
*moveList++ = make_move(ksq, pop_lsb(b));