A few positions to test movegen

[mar]

I have found a bug in my UCI setposition command trying your positions

That's excellent. So it wasn't useless to post it here

[Evert]

Very useful positions! I have tried JetChess 1.0.0.0 and it agrees with all the positions except the two first (avoid illegal en passant capture). Indeed it is a tricky position: JetChess gives Perft(1) = 9 (including cxd6 e.p.) and Perft(6) = 960427, including 136363 of cxd6 e.p.; of course 960427 - 136363 = 824064.

[d]8/5bk1/8/2Pp4/8/1K6/8/8 w - d6 0 1

1 c5-c6 119793
2 c5*d6e 136363
3 Kb3-c3 118973
4 Kb3-a3 82957
5 Kb3-a4 80828
6 Kb3-b4 97074
7 Kb3-a2 76150
8 Kb3-b2 119231
9 Kb3-c2 129058

Total: 960427

[d]8/8/1k6/8/2pP4/8/5BK1/8 b - d3 0 1

1 c4-c3 119793
2 c4*d3e 136363
3 kb6-c6 118973
4 kb6-a6 82957
5 kb6-a5 80828
6 kb6-b5 97074
7 kb6-a7 76150
8 kb6-b7 119231
9 kb6-c7 129058

Total: 960427

In view of that, must I think that JetChess is buggy in some rare/extreme cases? I was able to compute Perft(11) after 1.- f3, f6 (~1.1653e+15) and my result agree with Steven Edward's result. Thanks in advance.

Astounding.
I ran the position through Jazz, Sjaak and Leonidas and all three of them gave a different answer (969854, 824064 and 970952 respectively)!

After fixing the bug in Jazz and Leonidas that failed to recognise the en-passant capture as illegal (hmm... did I fix it, I wonder? Perhaps not entirely, better check), they all agree that the correct result is 824064.

Indeed, a VERY useful set of positions to have available!

On a technical note though: the FEN position is only supposed to include the en-passant square if the en-passant capture is legal, which isn't the case here. In fact, the position where the en-passant capture is possible is an illegal position, since white would have been in check prior to black's previous move...

EDIT: and on that note, thinking about it for a bit longer, the situation can't actually occur in a real game, so I should probably take out my "fix" again since it's not free...

[Evert]

Also try this one:

[d]3k4/8/8/K1Pp3r/8/8/8/8 w - d6 0 1

Here the white pawn cannot take ep on d6 due to the discovered check. The point being, after both pieces are removed from the board there is discovered check.

Steve

Thanks Steve.
This is actually the same case as the first two testpositions.

Martin

Not quite - the one where en-passant capture is impossible due to a discovered check by a bishop can't actually occur in a game.

[mar]

Not quite - the one where en-passant capture is impossible due to a discovered check by a bishop can't actually occur in a game.

Yes Evert, excellent point.
I think these positions should be used instead (Steve's position before black pushes the pawn by two):

Code: Select all

3k4/3p4/8/K1P4r/8/8/8/8 b - - 0 1			perft 6 = 1134888
8/8/8/8/k1p4R/8/3P4/3K4 w - - 0 1			perft 6 = 1134888

EDIT: I apologize for the first two positions that can't occur in a game. JetChess has the above positions right so it works just fine (no bug).
OTOH, it's probably a good idea to remove illegal ep flags when parsing a fen to avoid any potential problems.

[Ajedrecista]

Hello:

Also try this one:

[d]3k4/8/8/K1Pp3r/8/8/8/8 w - d6 0 1

Here the white pawn cannot take ep on d6 due to the discovered check. The point being, after both pieces are removed from the board there is discovered check.

Steve

@Steve: here are the results obtained with JetChess 1.0.0.0:

Code: Select all

Perft(1):

Total:                6

-----------------------

Perft(2):

  1   c5-c6          15
  2  Ka5-b5          16
  3  Ka5-a6          16
  4  Ka5-b6          15
  5  Ka5-a4          16
  6  Ka5-b4          16

Total:               94

-----------------------

Perft(3):

  1   c5-c6          84
  2  Ka5-b5         104
  3  Ka5-a6          90
  4  Ka5-b6         101
  5  Ka5-a4          92
  6  Ka5-b4         107

Total:              578

-----------------------

Perft(4):

  1   c5-c6        1284
  2  Ka5-b5        1788
  3  Ka5-a6        1544
  4  Ka5-b6        1716
  5  Ka5-a4        1617
  6  Ka5-b4        1884

Total:             9833

-----------------------

Perft(5):

  1   c5-c6        7887
  2  Ka5-b5       10322
  3  Ka5-a6        8977
  4  Ka5-b6        9853
  5  Ka5-a4        9710
  6  Ka5-b4       11815

Total:            58564

-----------------------

Perft(6):

  1   c5-c6      127497
  2  Ka5-b5      182011
  3  Ka5-a6      156082
  4  Ka5-b6      171667
  5  Ka5-a4      172818
  6  Ka5-b4      210405

Total:          1020480

-----------------------

Perft(7):

  1   c5-c6      813149
  2  Ka5-b5     1076774
  3  Ka5-a6      868915
  4  Ka5-b6      971993
  5  Ka5-a4     1053199
  6  Ka5-b4     1300034

Total:          6084064

-----------------------

Perft(8):

  1   c5-c6    13462794
  2  Ka5-b5    19060051
  3  Ka5-a6    15285404
  4  Ka5-b6    17090279
  5  Ka5-a4    18847515
  6  Ka5-b4    23265216

Total:        107011259

-----------------------

Perft(9):

  1   c5-c6    96519583
  2  Ka5-b5   113067366
  3  Ka5-a6    87738992
  4  Ka5-b6    98696639
  5  Ka5-a4   114799308
  6  Ka5-b4   143581817

Total:        654403705

-----------------------

Perft(10):

  1   c5-c6  1618387456
  2  Ka5-b5  2009557285
  3  Ka5-a6  1553104440
  4  Ka5-b6  1747957136
  5  Ka5-a4  2053840467
  6  Ka5-b4  2568985667

Total:      11551832451

------------------------

Perft(11):

  1   c5-c6  14269338389
  2  Ka5-b5  12437781979
  3  Ka5-a6   9387217977
  4  Ka5-b6  10641341547
  5  Ka5-a4  12835876918
  6  Ka5-b4  16184139001

Total:       75755695811

------------------------

Perft(12):

  1   c5-c6  239303947094
  2  Ka5-b5  221125944407
  3  Ka5-a6  166887447674
  4  Ka5-b6  189184338673
  5  Ka5-a4  229364060043
  6  Ka5-b4  289214154340

Total:      1335079892231

--------------------------

Perft(13):

  1   c5-c6  2755115218394
  2  Ka5-b5  1487534432704
  3  Ka5-a6  1119872389618
  4  Ka5-b6  1277278878192
  5  Ka5-a4  1533937202336
  6  Ka5-b4  1944788321613

Total:      10118526442857

---------------------------

Perft(14):

  1   c5-c6  45738172275508
  2  Ka5-b5  26325276908553
  3  Ka5-a6  19824853252447
  4  Ka5-b6  22613834399082
  5  Ka5-a4  27245485708371
  6  Ka5-b4  34543305291286

Total:      176290927835247

----------------------------

Perft(15):

  1   c5-c6  662866706386728
  2  Ka5-b5  208447628762504
  3  Ka5-a6  160018485567407
  4  Ka5-b6  183410599918419
  5  Ka5-a4  209279190800428
  6  Ka5-b4  265146632375909

Total:      1689169243811395

------------------------------

Perft(16):

  1   c5-c6  10845718850029518
  2  Ka5-b5   3633206864174363
  3  Ka5-a6   2786662949577909
  4  Ka5-b6   3193787429941721
  5  Ka5-a4   3663758710005513
  6  Ka5-b4   4643588151781907

Total:       28766722955510931

JetChess does not consider cxd6 e.p. (Evert also noted it). I hope that these numbers are the same as yours.

------------------------

Hi Jesus,

I'm glad you find it useful.
Yes this is a Jetchess bug for sure. I would be careful using that (perhaps you should contact the author and report a bug?).
Of course, when you calculate from startposition, you probably won't reach such case in first n plies (where n can be large).

Martin

@Martin: Thomas Zipproth is a member of TalkChess but he is not very active regarding number of posts. I did a report a while ago, noting problems with the order of castle rights (KQ and QK give different results in JetChess) and Thomas answered me saying that it is due to a FEN parsing bug. However, the last and only public release is 1.0.0.0 version from year 2006. I have not found other major bugs until I saw this interesting thread.

Regards from Spain.

Ajedrecista.

[mar]

Fixed version of all positions (removed illegal first two):

Code: Select all

// avoid illegal ep (thanks to Steve Maughan):
3k4/3p4/8/K1P4r/8/8/8/8 b - - 0 1			perft 6 = 1134888
8/8/8/8/k1p4R/8/3P4/3K4 w - - 0 1			perft 6 = 1134888
// avoid illegal ep #2
8/8/4k3/8/2p5/8/B2P2K1/8 w - - 0 1			perft 6 = 1015133
8/b2p2k1/8/2P5/8/4K3/8/8 b - - 0 1			perft 6 = 1015133
en passant capture checks opponent:
8/8/1k6/2b5/2pP4/8/5K2/8 b - d3 0 1			perft 6 = 1440467
8/5k2/8/2Pp4/2B5/1K6/8/8 w - d6 0 1			perft 6 = 1440467
short castling gives check:
5k2/8/8/8/8/8/8/4K2R w K - 0 1				perft 6 = 661072
4k2r/8/8/8/8/8/8/5K2 b k - 0 1				perft 6 = 661072
long castling gives check:
3k4/8/8/8/8/8/8/R3K3 w Q - 0 1				perft 6 = 803711
r3k3/8/8/8/8/8/8/3K4 b q - 0 1				perft 6 = 803711
castling (including losing cr due to rook capture):
r3k2r/1b4bq/8/8/8/8/7B/R3K2R w KQkq - 0 1	perft 4 = 1274206
r3k2r/7b/8/8/8/8/1B4BQ/R3K2R b KQkq - 0 1 	perft 4 = 1274206
castling prevented:
r3k2r/8/3Q4/8/8/5q2/8/R3K2R b KQkq - 0 1	perft 4 = 1720476
r3k2r/8/5Q2/8/8/3q4/8/R3K2R w KQkq - 0 1	perft 4 = 1720476
promote out of check:
2K2r2/4P3/8/8/8/8/8/3k4 w - - 0 1			perft 6 = 3821001
3K4/8/8/8/8/8/4p3/2k2R2 b - - 0 1			perft 6 = 3821001
discovered check:
8/8/1P2K3/8/2n5/1q6/8/5k2 b - - 0 1			perft 5 = 1004658
5K2/8/1Q6/2N5/8/1p2k3/8/8 w - - 0 1			perft 5 = 1004658
promote to give check:
4k3/1P6/8/8/8/8/K7/8 w - - 0 1				perft 6 = 217342
8/k7/8/8/8/8/1p6/4K3 b - - 0 1				perft 6 = 217342
underpromote to check:
8/P1k5/K7/8/8/8/8/8 w - - 0 1				perft 6 = 92683
8/8/8/8/8/k7/p1K5/8 b - - 0 1				perft 6 = 92683
self stalemate:
K1k5/8/P7/8/8/8/8/8 w - - 0 1				perft 6 = 2217
8/8/8/8/8/p7/8/k1K5 b - - 0 1				perft 6 = 2217
stalemate/checkmate:
8/k1P5/8/1K6/8/8/8/8 w - - 0 1				perft 7 = 567584
8/8/8/8/1k6/8/K1p5/8 b - - 0 1				perft 7 = 567584
double check:
8/8/2k5/5q2/5n2/8/5K2/8 b - - 0 1			perft 4 = 23527
8/5k2/8/5N2/5Q2/2K5/8/8 w - - 0 1			perft 4 = 23527

[Volker Annuss]

short castling impossible although the rook never moved away from its corner
1k6/1b6/8/8/7R/8/8/4K2R b K - 0 1 perft 5 = 1063513
4k2r/8/8/7r/8/8/1B6/1K6 w k - 0 1 perft 5 = 1063513

long castling impossible although the rook never moved away from its corner
1k6/8/8/8/R7/1n6/8/R3K3 b Q - 0 1 perft 5 = 346695
r3k3/8/1N6/r7/8/8/8/1K6 w q - 0 1 perft 5 = 346695

[d]

[Sven]

short castling impossible although the rook never moved away from its corner
1k6/1b6/8/8/7R/8/8/4K2R b K - 0 1 perft 5 = 1063513
4k2r/8/8/7r/8/8/1B6/1K6 w k - 0 1 perft 5 = 1063513

long castling impossible although the rook never moved away from its corner
1k6/8/8/8/R7/1n6/8/R3K3 b Q - 0 1 perft 5 = 346695
r3k3/8/1N6/r7/8/8/8/1K6 w q - 0 1 perft 5 = 346695

[d]

I do not understand what you mean. If both king and rook are on their original squares but the FEN does not include the corresponding castling right then one of the two pieces actually DID move prior to that position.

Sven

[Sven]

short castling impossible although the rook never moved away from its corner
1k6/1b6/8/8/7R/8/8/4K2R b K - 0 1 perft 5 = 1063513
4k2r/8/8/7r/8/8/1B6/1K6 w k - 0 1 perft 5 = 1063513

long castling impossible although the rook never moved away from its corner
1k6/8/8/8/R7/1n6/8/R3K3 b Q - 0 1 perft 5 = 346695
r3k3/8/1N6/r7/8/8/8/1K6 w q - 0 1 perft 5 = 346695

[d]

I do not understand what you mean. If both king and rook are on their original squares but the FEN does not include the corresponding castling right then one of the two pieces actually DID move prior to that position.

Sven

I should add: in the first two of your positions there is no reason for short castling not being allowed, other than the FEN stating so. A rook being attacked does not already prevent you from castling. An available castling right is temporarily unavailable if either
- one of the squares between king and rook is occupied, or
- the king is in check, or
- the king would jump over an attacked square when castling,
- or of course the king would be in check after castling (this is no special case).
So short castling with an attacked h-rook can be possible as well as long castling with an attacked a-rook or an attacked square b1/b8.

Sven

[Evert]

I should add: in the first two of your positions there is no reason for short castling not being allowed, other than the FEN stating so. A rook being attacked does not already prevent you from castling.

I was confused about the point of those positions too when I first saw them, more so when I ran them through my perft function and got the quoted count.

The point is not that it's illegal to castle when the rook is attacked. Note that the side to move is not the side that can castle. The point is that after 1... BxR 2. RxB, the rook is no longer the original rook. So although the original rook never moved, the rook that is now in its place did and castling is not allowed. The point of the test is whether the castling rights are properly removed when the rook is captured.