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Do not exit early even when seeing mate

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Fixes the reported KNNK ending problem:

http://talkchess.com/forum/viewtopic.php?t=39347

Joona says:

Now I finally had a time to take a look at on this issue.

I've reproduced the problem starting from this position:
1B6/1B2k3/P7/1P3p2/1K6/8/4b3/4b3 w - - 6 85

I made Stockfish play as white and Fruit as black.
I repeated test ten times and once SF was not able to deliver mate.

But I observed several times that SF had reported on last something like mate in 10.
However next time it played move with score mate in 15.

Easiest way to solve the problem is attached as a patch. I tested it several times and SF always
ended up playing the optimal move. Of course the downside is that now delivering mate
takes a bit longer, but IMO it's better to lose once in a while by time in sudden death
game than not being able to deliver simple mate with long time controls.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Joona Kiiski 2011-07-23 22:18:28 +01:00 • committed by Marco Costalba
parent a1f9bf19d9
commit a6fc3d6ee5
1 changed files with 0 additions and 6 deletions
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6
src/search.cpp
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@ -633,12 +633,6 @@ namespace {
// Check for some early stop condition // Check for some early stop condition
if (!StopRequest && Limits.useTimeManagement()) if (!StopRequest && Limits.useTimeManagement())
{ {
// Stop search early when the last two iterations returned a mate score
if ( depth >= 5
&& abs(bestValues[depth]) >= VALUE_MATE_IN_PLY_MAX
&& abs(bestValues[depth - 1]) >= VALUE_MATE_IN_PLY_MAX)
StopRequest = true;
// Stop search early if one move seems to be much better than the // Stop search early if one move seems to be much better than the
// others or if there is only a single legal move. Also in the latter // others or if there is only a single legal move. Also in the latter
// case we search up to some depth anyway to get a proper score. // case we search up to some depth anyway to get a proper score.