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Allowing singular extension in mate positions

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Drop useless condition

abs(ttValue) < VALUE_KNOWN_WIN

And extend singular extension search to cases when ttValue
stores a mate score. This improves mate finding and does
not introduce any regression.

Yery tested this patch against current master on the 6500+
Chest mate suite with 200K fixed nodes:

    shortest mates found: master: 1206 patch:1205
    any mate found: master: 1903 patch: 2003

with 1 sec time:

    shortest mates found: master: 2667 patch: 2628
    any mate found: master: 3585 patch: 3646

Verified for no regression:

STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 25655 W: 4578 L: 4465 D: 16612

LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 66247 W: 8618 L: 8557 D: 49072

bench: 6335042
This commit is contained in:
joergoster 2016-09-21 14:02:35 +02:00 • committed by Marco Costalba
parent 8662bdfa12
commit 351844061e
1 changed files with 2 additions and 3 deletions
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5
src/search.cpp
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@ -845,8 +845,7 @@ moves_loop: // When in check search starts from here
singularExtensionNode = !rootNode
&& depth >= 8 * ONE_PLY
&& ttMove != MOVE_NONE
/* && ttValue != VALUE_NONE Already implicit in the next condition */
&& abs(ttValue) < VALUE_KNOWN_WIN
&& ttValue != VALUE_NONE
&& !excludedMove // Recursive singular search is not allowed
&& (tte->bound() & BOUND_LOWER)
&& tte->depth() >= depth - 3 * ONE_PLY;
@ -904,7 +903,7 @@ moves_loop: // When in check search starts from here
&& !extension
&& pos.legal(move))
{
Value rBeta = ttValue - 2 * depth / ONE_PLY;
Value rBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE);
Depth d = (depth / (2 * ONE_PLY)) * ONE_PLY;
ss->excludedMove = move;
ss->skipEarlyPruning = true;