Fix syzygy with partial TB

In case we have installed a not complete set of 6-men tables and
there is 6 piece position on board, but no corresponding
tablebase engine is not using any syzygy at all.

Reported by Jouni Uski, fix by Peter Österlund,
confirmed as a bug by Ronald de Man.

bench: 7591630

diff --git a/src/search.cpp b/src/search.cpp
index c12f086240721cc9c7157032eb5864ea87103268..fe450a4e9adc2956128e1dd787c319dcc06b9dff 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1641,7 +1641,7 @@ void Tablebases::filter_root_moves(Position& pos, Search::RootMoves& rootMoves)
         RootInTB = root_probe_wdl(pos, rootMoves, TB::Score);
 
         // Only probe during search if winning
-        if (TB::Score <= VALUE_DRAW)
+        if (RootInTB && TB::Score <= VALUE_DRAW)
             Cardinality = 0;
     }