Refine deeper post-lmr searches

Vizvezdenec · vondele · commit 65e2150501b8 · 2023-05-07T22:36:57.000+02:00
This patch improves logic conditions for performing deeper searches after passed LMR. Instead of exceeding alpha by some margin now it requires to exceed the current best value - which may be lower than alpha (but never bigger since we update alpha with bestvalue if it exceeds alpha). Passed STC: https://tests.stockfishchess.org/tests/view/6455f78008858de8313775b6 LLR: 2.94 (-2.94,2.94) <0.00,2.00> Total: 209344 W: 55993 L: 55448 D: 97903 Ptnml(0-2): 507, 22798, 57526, 23325, 516 Passed LTC: https://tests.stockfishchess.org/tests/view/64572d46eb75932ccfebff97 LLR: 2.94 (-2.94,2.94) <0.50,2.50> Total: 66288 W: 17867 L: 17514 D: 30907 Ptnml(0-2): 21, 6240, 20269, 6593, 21 closes #4559 bench 3808503
diff --git a/src/search.cpp b/src/search.cpp
@@ -1201,7 +1201,7 @@ namespace {
           {
               // Adjust full depth search based on LMR results - if result
               // was good enough search deeper, if it was bad enough search shallower
-              const bool doDeeperSearch = value > (alpha + 58 + 12 * (newDepth - d));
+              const bool doDeeperSearch = value > (bestValue + 68 + 12 * (newDepth - d));
               const bool doEvenDeeperSearch = value > alpha + 588 && ss->doubleExtensions <= 5;
               const bool doShallowerSearch = value < bestValue + newDepth;
 

Original file line number	Diff line number	Diff line change
`@@ -1201,7 +1201,7 @@ namespace {`
`1201`	`1201`	`{`
`1202`	`1202`	`// Adjust full depth search based on LMR results - if result`
`1203`	`1203`	`// was good enough search deeper, if it was bad enough search shallower`
`1204`		`- const bool doDeeperSearch = value > (alpha + 58 + 12 * (newDepth - d));`
	`1204`	`+ const bool doDeeperSearch = value > (bestValue + 68 + 12 * (newDepth - d));`
`1205`	`1205`	`const bool doEvenDeeperSearch = value > alpha + 588 && ss->doubleExtensions <= 5;`
`1206`	`1206`	`const bool doShallowerSearch = value < bestValue + newDepth;`
`1207`	`1207`