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Tweak null move pruning conditions

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Allow null move pruning only if last stat score < 30000.

Passed STC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 12653 W: 2641 L: 2454 D: 7558
http://tests.stockfishchess.org/tests/view/5af1d8830ebc5968e6523edb

Passed LTC:
LLR: 2.97 (-2.94,2.94) [0.00,5.00]
Total: 19782 W: 3072 L: 2878 D: 13832
http://tests.stockfishchess.org/tests/view/5af1ee8c0ebc5968e6523ee4

Ideas for further work:

• Tune the stat score threshold.
• Try depth based stat score threshold.
• Try stat score condition for other prunings.

Closes https://github.com/official-stockfish/Stockfish/pull/1589

Bench: 5088156
This commit is contained in:
Stefan Geschwentner 2018-05-08 19:03:22 +02:00 • committed by Stéphane Nicolet
parent 6634f41ac9
commit de0889612f
1 changed files with 1 additions and 0 deletions
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1
src/search.cpp
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@ -737,6 +737,7 @@ namespace {
// Step 9. Null move search with verification search (~40 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
&& (ss-1)->statScore < 30000
&& eval >= beta
&& ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
&& (ss->ply >= thisThread->nmp_ply || ss->ply % 2 != thisThread->nmp_odd))