Retire undo_null_move()

Use a templetized do_null_move() to do/undo the null move.

No functional change.

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

src/position.cpp

@@ -1204,61 +1204,48 @@ void Position::undo_move(Move m) {
 }
 
 
-/// Position::do_null_move makes() a "null move": It switches the side to move
+/// Position::do_null_move() is used to do/undo a "null move": It flips the side
-/// and updates the hash key without executing any move on the board.
+/// to move and updates the hash key without executing any move on the board.
-
+template<bool Do>
 void Position::do_null_move(StateInfo& backupSt) {
 
   assert(!in_check());
 
   // Back up the information necessary to undo the null move to the supplied
-  // StateInfo object.
+  // StateInfo object. Note that differently from normal case here backupSt
-  // Note that differently from normal case here backupSt is actually used as
+  // is actually used as a backup storage not as the new state. This reduces
-  // a backup storage not as a new state to be used.
+  // the number of fields to be copied.
-  backupSt.key      = st->key;
+  StateInfo* src = Do ? st : &backupSt;
-  backupSt.epSquare = st->epSquare;
+  StateInfo* dst = Do ? &backupSt : st;
-  backupSt.value    = st->value;
-  backupSt.previous = st->previous;
-  backupSt.pliesFromNull = st->pliesFromNull;
-  st->previous = &backupSt;
 
-  // Update the necessary information
+  dst->key      = src->key;
-  if (st->epSquare != SQ_NONE)
+  dst->epSquare = src->epSquare;
-      st->key ^= zobEp[st->epSquare];
+  dst->value    = src->value;
-
+  dst->rule50   = src->rule50;
-  st->key ^= zobSideToMove;
+  dst->pliesFromNull = src->pliesFromNull;
-  prefetch((char*)TT.first_entry(st->key));
 
   sideToMove = flip(sideToMove);
-  st->epSquare = SQ_NONE;
+
-  st->rule50++;
+  if (Do)
-  st->pliesFromNull = 0;
+  {
-  st->value += (sideToMove == WHITE) ?  TempoValue : -TempoValue;
+      if (st->epSquare != SQ_NONE)
+          st->key ^= zobEp[st->epSquare];
+
+      st->key ^= zobSideToMove;
+      prefetch((char*)TT.first_entry(st->key));
+
+      st->epSquare = SQ_NONE;
+      st->rule50++;
+      st->pliesFromNull = 0;
+      st->value += (sideToMove == WHITE) ?  TempoValue : -TempoValue;
+  }
 
   assert(pos_is_ok());
 }
 
-
+// Explicit template instantiations
-/// Position::undo_null_move() unmakes a "null move".
+template void Position::do_null_move<false>(StateInfo& backupSt);
-
+template void Position::do_null_move<true>(StateInfo& backupSt);
-void Position::undo_null_move() {
-
-  assert(!in_check());
-
-  // Restore information from the our backup StateInfo object
-  StateInfo* backupSt = st->previous;
-  st->key      = backupSt->key;
-  st->epSquare = backupSt->epSquare;
-  st->value    = backupSt->value;
-  st->previous = backupSt->previous;
-  st->pliesFromNull = backupSt->pliesFromNull;
-
-  // Update the necessary information
-  sideToMove = flip(sideToMove);
-  st->rule50--;
-
-  assert(pos_is_ok());
-}
 
 
 /// Position::see() is a static exchange evaluator: It tries to estimate the

src/position.h

@@ -166,8 +166,7 @@ public:
   void do_move(Move m, StateInfo& st);
   void do_move(Move m, StateInfo& st, const CheckInfo& ci, bool moveIsCheck);
   void undo_move(Move m);
-  void do_null_move(StateInfo& st);
+  template<bool Do> void do_null_move(StateInfo& st);
-  void undo_null_move();
 
   // Static exchange evaluation
   int see(Move m) const;

src/search.cpp

@@ -870,12 +870,12 @@ namespace {
         if (refinedValue - PawnValueMidgame > beta)
             R++;
 
-        pos.do_null_move(st);
+        pos.do_null_move<true>(st);
         (ss+1)->skipNullMove = true;
         nullValue = depth-R*ONE_PLY < ONE_PLY ? -qsearch<NonPV>(pos, ss+1, -beta, -alpha, DEPTH_ZERO)
                                               : - search<NonPV>(pos, ss+1, -beta, -alpha, depth-R*ONE_PLY);
         (ss+1)->skipNullMove = false;
-        pos.undo_null_move();
+        pos.do_null_move<false>(st);
 
         if (nullValue >= beta)
         {