X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fsearch.cpp;h=ca5a107ea2853df9b3648eeb3f4e56bb23c039b6;hp=f132e3ecc03307269030299443dcf931233b5108;hb=71cc01c2ef45bab91bdcd72c699f66e19dd518b3;hpb=16b31bb249ccb9f4f625001f9772799d286e2f04

diff --git a/src/search.cpp b/src/search.cpp
index f132e3ec..ca5a107e 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -742,7 +742,18 @@ namespace {
                 assert(depth >= 5 * ONE_PLY);
 
                 pos.do_move(move, st);
-                value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
+
+                // Perform a preliminary search at depth 1 to verify that the move holds.
+                // We will only do this search if the depth is not 5, thus avoiding two
+                // searches at depth 1 in a row.
+                if (depth != 5 * ONE_PLY)
+                    value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, ONE_PLY, !cutNode, true);
+
+                // If the first search was skipped or was performed and held, perform
+                // the regular search.
+                if (depth == 5 * ONE_PLY || value >= rbeta)
+                    value = -search<NonPV>(pos, ss+1, -rbeta, -rbeta+1, depth - 4 * ONE_PLY, !cutNode, false);
+
                 pos.undo_move(move);
                 if (value >= rbeta)
                     return value;