Add a qsearch limit against too deep recursion (#958)

Closes #957.

Author: ianfab

src/search.cpp

@@ -1554,6 +1554,10 @@ namespace {
     if (ss->ply >= MAX_PLY)
         return !ss->inCheck ? evaluate(pos) : VALUE_DRAW;
 
+    // Safeguard against too deep recursions in quiescence search
+    if (depth < DEPTH_QS_MAX && !ss->inCheck)
+        return evaluate(pos);
+
     assert(0 <= ss->ply && ss->ply < MAX_PLY);
 
     // Decide whether or not to include checks: this fixes also the type of

src/types.h

@@ -484,6 +484,7 @@ enum : int {
   DEPTH_QS_CHECKS     =  0,
   DEPTH_QS_NO_CHECKS  = -1,
   DEPTH_QS_RECAPTURES = -5,
+  DEPTH_QS_MAX        = -32,
 
   DEPTH_NONE   = -6,