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Skip evaluate() call after a null move

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Reuse the evaluation of the parent with inverted sign and
set margin to zero (this is an hack!).

This is done only in qsearch where almost 15% of calls are
from a null move. In normal search the number of nodes where

(ss-1)->currentMove == MOVE_NULL

is almost zero and so there is no need of using this trick.

The big advantage of this patch is a speed-up due to skipped
evaluate() calls, that are very costly.

Functionality is of course affected and we will need to proper
test it later. For now we just register a 3-4% speed up.

Suggested by Hongzhi Cheng.

bench: 5051328
This commit is contained in:
Marco Costalba 2012-11-04 10:21:40 +01:00
parent a87831230d
commit 37e9802411
1 changed files with 5 additions and 0 deletions
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5
src/search.cpp
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@ -1154,6 +1154,11 @@ split_point_start: // At split points actual search starts from here
if (ss->staticEval == VALUE_NONE || ss->evalMargin == VALUE_NONE) // Due to a race
ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
}
else if ((ss-1)->currentMove == MOVE_NULL)
{
ss->staticEval = bestValue = -(ss-1)->staticEval;
ss->evalMargin = VALUE_ZERO; // Hack, we really don't know the value
}
else
ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);