Introduce pre-qsearch ttmove extensions at pv nodes

Vizvezdenec · vondele · commit 836154acb5ba · 2024-07-23T19:24:00.000+02:00
The idea is that we are about to dive into qsearch (next search depth is <= 0) but since we have the move in transposition table we should extend that move and evaluate it with more precise search - because branch seems important. Passed STC: https://tests.stockfishchess.org/tests/view/6699d2564ff211be9d4ec488 LLR: 2.93 (-2.94,2.94) <0.00,2.00> Total: 83104 W: 21789 L: 21401 D: 39914 Ptnml(0-2): 293, 9748, 21128, 10044, 339 Passed LTC: https://tests.stockfishchess.org/tests/view/669b3f1a4ff211be9d4ec602 LLR: 2.94 (-2.94,2.94) <0.50,2.50> Total: 136098 W: 34636 L: 34111 D: 67351 Ptnml(0-2): 105, 14882, 37550, 15407, 105 closes #5512 bench 1526129
diff --git a/src/search.cpp b/src/search.cpp
@@ -1206,6 +1206,10 @@ Value Search::Worker::search(
             (ss + 1)->pv    = pv;
             (ss + 1)->pv[0] = Move::none();
 
+            // Extend move from transposition table if we are about to dive into qsearch.
+            if (move == ttData.move && ss->ply <= thisThread->rootDepth * 2)
+                newDepth = std::max(newDepth, 1);
+
             value = -search<PV>(pos, ss + 1, -beta, -alpha, newDepth, false);
         }
 

Original file line number	Diff line number	Diff line change
`@@ -1206,6 +1206,10 @@ Value Search::Worker::search(`
`1206`	`1206`	`(ss + 1)->pv = pv;`
`1207`	`1207`	`(ss + 1)->pv[0] = Move::none();`
`1208`	`1208`
	`1209`	`+ // Extend move from transposition table if we are about to dive into qsearch.`
	`1210`	`+ if (move == ttData.move && ss->ply <= thisThread->rootDepth * 2)`
	`1211`	`+ newDepth = std::max(newDepth, 1);`
	`1212`	`+`
`1209`	`1213`	`value = -search<PV>(pos, ss + 1, -beta, -alpha, newDepth, false);`
`1210`	`1214`	`}`
`1211`	`1215`