Fix Singular extension condition to handle mate scores

joergoster · zamar · commit ffedfa33542a · 2014-06-29T20:17:40.000+01:00
With Eelco's patch "Don't special case for abs(beta) &gt;= VALUE_MATE_IN_MAX_PLY" condition "abs(ttValue) &lt; VALUE_KNOWN_WIN" has been removed from singular extension search, and condition "abs(beta) &lt; VALUE_KNOWN_WIN" was added to the SingularExtensionNode definition.
This might lead to problems, especially in positions, where a mate is due.
For example, this position 5rk1/4K1pp/8/5PPP/8/8/8/1R6 w - - 12 1 triggers an assert.
stockfish: search.cpp:434: Value {anonymous}::search(Position&amp;, Search::Stack*, Value, Value, Depth, bool) [with {anonymous}::NodeType NT = (&lt;unnamed&gt;::NodeType)2u; bool SpNode = false]: Assertion `-VALUE_INFINITE &lt;= alpha &amp;&amp; alpha &lt; beta &amp;&amp; beta &lt;= VALUE_INFINITE' failed.

So let's re-insert the removed condition.
First spotted by Uri Blass, fix by me.

Bench: 8759675
diff --git a/src/search.cpp b/src/search.cpp
@@ -700,7 +700,8 @@ namespace {
                            &&  depth >= 8 * ONE_PLY
                            &&  abs(beta) < VALUE_KNOWN_WIN
                            &&  ttMove != MOVE_NONE
-                           &&  ttValue != VALUE_NONE
+                       /*  &&  ttValue != VALUE_NONE Already implicit in the next condition */
+                           &&  abs(ttValue) < VALUE_KNOWN_WIN
                            && !excludedMove // Recursive singular search is not allowed
                            && (tte->bound() & BOUND_LOWER)
                            &&  tte->depth() >= depth - 3 * ONE_PLY;
