Skip draw by repetition check in qsearch

Cut in half the time spent in pos.draw() that accounts
for a whopping 1% of total time !

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/position.cpp

@@ -1778,7 +1778,7 @@ Value Position::compute_non_pawn_material(Color c) const {
 /// Position::is_draw() tests whether the position is drawn by material,
 /// repetition, or the 50 moves rule. It does not detect stalemates, this
 /// must be done by the search.
-
+template<bool SkipRepetition>
 bool Position::is_draw() const {
 
   // Draw by material?
@@ -1791,13 +1791,18 @@ bool Position::is_draw() const {
       return true;
 
   // Draw by repetition?
-  for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
-      if (history[st->gamePly - i] == st->key)
-          return true;
+  if (!SkipRepetition)
+      for (int i = 4, e = Min(Min(st->gamePly, st->rule50), st->pliesFromNull); i <= e; i += 2)
+          if (history[st->gamePly - i] == st->key)
+              return true;
 
   return false;
 }
 
+// Explicit template instantiations
+template bool Position::is_draw<false>() const;
+template bool Position::is_draw<true>() const;
+
 
 /// Position::is_mate() returns true or false depending on whether the
 /// side to move is checkmated.

src/position.h

@@ -228,7 +228,7 @@ public:
 
   // Game termination checks
   bool is_mate() const;
-  bool is_draw() const;
+  template<bool SkipRepetition> bool is_draw() const;
 
   // Number of plies from starting position
   int startpos_ply_counter() const;

src/search.cpp

@@ -763,7 +763,7 @@ namespace {
 
     // Step 2. Check for aborted search and immediate draw
     if ((   StopRequest
-         || pos.is_draw()
+         || pos.is_draw<false>()
          || ss->ply > PLY_MAX) && !RootNode)
         return VALUE_DRAW;
 
@@ -1333,7 +1333,7 @@ split_point_start: // At split points actual search starts from here
     ss->ply = (ss-1)->ply + 1;
 
     // Check for an instant draw or maximum ply reached
-    if (ss->ply > PLY_MAX || pos.is_draw())
+    if (pos.is_draw<true>() || ss->ply > PLY_MAX)
         return VALUE_DRAW;
 
     // Decide whether or not to include checks, this fixes also the type of
@@ -2019,7 +2019,7 @@ split_point_start: // At split points actual search starts from here
            && pos.move_is_pl(tte->move())
            && pos.pl_move_is_legal(tte->move(), pos.pinned_pieces(pos.side_to_move()))
            && ply < PLY_MAX
-           && (!pos.is_draw() || ply < 2))
+           && (!pos.is_draw<false>() || ply < 2))
     {
         pv[ply] = tte->move();
         pos.do_move(pv[ply++], *st++);